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<h1>EPICS R3.14 Channel Access Reference Manual</h1>
<address>
Jeffrey O. Hill
</address>
<p><span style="font-size: x-small; font-weight:lighter;">Los Alamos National
Laboratory, SNS Division</span></p>
<address>
Ralph Lange
</address>
<p><span style="font-size: x-small; font-weight:lighter;">Helmholtz-Zentrum
Berlin (BESSY II)</span></p>
<p><span style="font-size: xx-small; font-weight:lighter;">Copyright © 2009
Helmholtz-Zentrum Berlin für Materialien und Energie GmbH.<br>
Copyright © 2002 The University of Chicago, as Operator of Argonne National
Laboratory.<br>
Copyright © 2002 The Regents of the University of California, as Operator of
Los Alamos National Laboratory.<br>
Copyright © 2002 Berliner Speicherringgesellschaft für Synchrotronstrahlung
GmbH.</span></p>
<p><span style="font-size: xx-small; font-weight:lighter;">EPICS BASE Versions
3.13.7 and higher are distributed subject to a Software License Agreement found
in the file LICENSE that is included with this distribution.</span></p>
<p><a href="http://www.w3.org/Amaya/"><img
src="http://www.w3.org/Amaya/Icons/w3c-amaya.gif" alt="W3C-Amaya" height="31"
width="88"></a> <a href="http://validator.w3.org/check/referer"><img
src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01!" height="31"
width="88"></a></p>
<p><small><span style="font-size: smaller; font-weight:lighter;">Modified on
$Date$</span></small></p>
<hr>
<h2>Table of Contents</h2>
<h3><a href="#Configuration">Configuration</a></h3>
<ul>
<li><a href="#EPICS">EPICS Environment Variables</a></li>
<li><a href="#CA and Wide Area Networks">CA and Wide Area Networks</a></li>
<li><a href="#Network">IP Network Administration Background
Information</a></li>
<li><a href="#port">IP port numbers</a></li>
<li><a href="#Environmen">WAN Environment</a></li>
<li><a href="#Disconnect">Disconnect Time Out Interval / Server Beacon
Period</a></li>
<li><a href="#Dynamic">Dynamic Changes in the CA Client Library Search
Interval</a></li>
<li><a href="#Configurin3">Configuring the Maximum Search Period</a></li>
<li><a href="#Repeater">The CA Repeater</a></li>
<li><a href="#Configurin">Configuring the Time Zone</a></li>
<li><a href="#Configurin1">Configuring the Maximum Array Size</a></li>
<li><a href="#Configurin2">Configuring a CA server</a></li>
</ul>
<h3><a href="#Building">Building an Application</a></h3>
<ul>
<li><a href="#Required1">Required Header (.h) Files</a></li>
<li><a href="#Required">Required Libraries</a></li>
<li><a href="#Compiler">Compiler and System Specific Build Options</a></li>
</ul>
<h3><a href="#CommandUtils">Command Line Utilities</a></h3>
<ul>
<li><a href="#acctst">acctst - CA client library regression test</a></li>
<li><a href="#caEventRat">caEventRate - PV event rate logging</a></li>
<li><a href="#casw">casw - CA server beacon anomaly logging</a></li>
<li><a href="#catime">catime - CA client library performance test</a></li>
<li><a href="#ca_test">ca_test - dump the value of a PV in each external data
type to the console</a></li>
<li><a href="#excas">excas - an example server</a></li>
</ul>
<h3 style=""><a href="#CommandTools">Command Line Tools</a></h3>
<ul style="">
<li><a href="#caget">caget - Get and print value for PVs</a></li>
<li><a href="#camonitor">camonitor - Set up monitor and continuously print
incoming values for PVs</a></li>
<li><a href="#caput">caput - Put value to a PV</a></li>
<li><a href="#cainfo">cainfo - Print all available channel status and
information for a PV</a></li>
</ul>
<h3><a href="#Troublesho">Troubleshooting</a></h3>
<ul>
<li><a href="#When">When Clients Do Not Connect to Their Server</a>
<ul>
<li><a href="#Broadcast">Client and Server Broadcast Addresses Dont
Match</a></li>
<li><a href="#Client">Client Isnt Configured to Use the Server's
Port</a></li>
<li><a href="#Unicast">Unicast Addresses in the EPICS_CA_ADDR_LIST Does
not Reliably Contact Servers Sharing the Same UDP Port on the Same
Host</a></li>
<li><a href="#Client1">Client Does not See Server's Beacons</a></li>
<li><a href="#Server1">A server's IP address was changed</a></li>
</ul>
</li>
<li><a href="#Requests">Put Requests Just Prior to Process Termination Appear
to be Ignored</a></li>
<li><a href="#Problems">ENOBUFS Messages</a></li>
</ul>
<h3><a href="#Function">Function Call Interface Guidelines</a></h3>
<ul>
<li><a href="#Flushing">Flushing and Blocking</a></li>
<li><a href="#Status">Status Codes</a></li>
<li><a href="#Channel">Channel Access Data Types</a></li>
<li><a href="#User">User Supplied Callback Functions</a></li>
<li><a href="#Channel1">Channel Access Exceptions</a></li>
<li><a href="#Server">Server and Client Share the Same Address Space on The
Same Host</a></li>
<li><a href="#Arrays">Arrays</a></li>
<li><a href="#Connection">Connection Management</a></li>
<li><a href="#Thread">Thread Safety and Preemptive Callback to User
Code</a></li>
<li><a href="#Client2">CA Client Contexts and Application Specific Auxillary
Threads</a></li>
<li><a href="#Polling">Polling the CA Client Library From Single Threaded
Applications</a></li>
<li><a href="#Avoid">Avoid Emulating Bad Practices that May Still be
Common</a></li>
<li><a href="#Calling">Calling CA Functions from the vxWorks Shell
Thread</a></li>
<li><a href="#Calling1">Calling CA Functions from POSIX signal
handlers</a></li>
</ul>
<h3>Functionality Index </h3>
<ul>
<li><a href="#ca_context_create">create CA client context</a></li>
<li><a href="#ca_context_destroy">terminate CA client context</a></li>
<li><a href="#ca_create_channel">create a channel</a></li>
<li><a href="#ca_clear_channel">delete a channel</a></li>
<li><a href="#ca_put">write to a channel</a></li>
<li><a href="#ca_put">write to a channel and wait for initiated activities to
complete</a></li>
<li><a href="#ca_get">read from a channel</a></li>
<li><a href="#ca_add_event">subscribe for state change updates</a></li>
<li><a href="#ca_clear_event">cancel a subscription</a></li>
<li><a href="#ca_pend_io">block for certain requests to complete</a></li>
<li><a href="#ca_test_io">test to see if certain requests have
completed</a></li>
<li><a href="#L3249">process CA client library background activities</a></li>
<li><a href="#ca_flush_io">flush outstanding requests to the server</a></li>
<li><a href="#ca_add_exception_event">replace the default exception
handler</a></li>
<li><a href="#ca_dump_db">dump dbr type to standard out</a></li>
</ul>
<h3><a href="#Function Call Reference">Function Call Interface Index</a></h3>
<ul>
<li><a href="#ca_add_exception_event">ca_add_exception_event</a></li>
<li><a href="#ca_add_fd_">ca_add_fd_registration</a></li>
<li><a href="#ca_get">ca_array_get</a></li>
<li><a href="#ca_get">ca_array_get_callback</a></li>
<li><a href="#ca_put">ca_array_put</a></li>
<li><a href="#ca_put">ca_array_put_callback</a></li>
<li><a href="#ca_attach_context">ca_attach_context </a></li>
<li><a href="#ca_clear_channel">ca_clear_channel</a></li>
<li><a href="#ca_clear_event">ca_clear_subscription</a></li>
<li><a href="#ca_client_status">ca_client_status</a></li>
<li><a href="#ca_context_create">ca_context_create</a></li>
<li><a href="#ca_context_destroy">ca_context_destroy</a></li>
<li><a href="CAref.html#ca_client_status">ca_context_status</a></li>
<li><a href="#ca_create_channel">ca_create_channel</a></li>
<li><a href="#ca_add_event">ca_create_subscription</a></li>
<li><a href="#ca_current_context">ca_current_context</a></li>
<li><a href="#ca_dump_db">ca_dump_dbr</a></li>
<li><a href="#ca_detach_">ca_detach_context</a></li>
<li><a href="#ca_element_count">ca_element_count</a></li>
<li><a href="#L6925">ca_field_type</a></li>
<li><a href="#ca_flush_io">ca_flush_io</a></li>
<li><a href="#ca_get">ca_get</a></li>
<li><a href="#ca_get">ca_get_callback</a></li>
<li><a href="#L6927">ca_host_name</a></li>
<li><a href="#L6929">ca_message</a></li>
<li><a href="#L6931">ca_name</a></li>
<li><a href="#L6933">ca_read_access</a></li>
<li><a href="#ca_replace">ca_replace_access_rights_event</a></li>
<li><a href="#ca_replace_printf_handler">ca_replace_printf_handler</a></li>
<li><a href="#L3249">ca_pend_event</a></li>
<li><a href="#ca_pend_io">ca_pend_io</a></li>
<li><a href="#L3249">ca_poll</a></li>
<li><a href="#ca_puser">ca_puser</a></li>
<li><a href="#ca_put">ca_put</a></li>
<li><a href="#ca_set_puser">ca_set_puser</a></li>
<li><a href="#ca_signal">ca_signal</a></li>
<li><a href="#ca_sg_block">ca_sg_block</a></li>
<li><a href="#ca_sg_create">ca_sg_create</a></li>
<li><a href="#ca_sg_delete">ca_sg_delete</a></li>
<li><a href="#ca_sg_get">ca_sg_array_get</a></li>
<li><a href="#ca_sg_put">ca_sg_array_put</a></li>
<li><a href="#ca_sg_reset">ca_sg_reset</a></li>
<li><a href="#ca_sg_test">ca_sg_test</a></li>
<li><a href="#ca_state">ca_state</a></li>
<li><a href="#ca_test_event">ca_test_event</a></li>
<li><a href="#ca_test_io">ca_test_io</a></li>
<li><a href="#L6941">ca_write_access</a></li>
<li><a href="#ca_state">channel_state</a></li>
<li><a href="#dbr_size[]">dbr_size[]</a></li>
<li><a href="#L6946">dbr_size_n</a></li>
<li><a href="#dbr_value_size">dbr_value_size[]</a></li>
<li><a href="#dbr_type_t">dbr_type_to_text</a></li>
<li><a href="#ca_signal">SEVCHK</a></li>
</ul>
<h3>Deprecated Function Call Interface Function Index</h3>
<ul>
<li><a href="#ca_add_event">ca_add_event</a></li>
<li><a href="#ca_clear_event">ca_clear_event</a></li>
<li><a href="#ca_create_channel">ca_search</a></li>
<li><a href="#ca_create_channel">ca_search_and_connect</a></li>
<li><a href="#ca_context_destroy">ca_task_exit</a></li>
<li><a href="#ca_context_create">ca_task_initialize</a></li>
</ul>
<h3><a href="#Return">Return Codes</a></h3>
<hr>
<h2><a name="Configuration"></a>Configuration</h2>
<h3>Why Reconfigure Channel Access</h3>
<p>Typically reasons to reconfigure EPICS Channel Access:</p>
<ul>
<li>Two independent control systems must share a network without fear of
interaction</li>
<li>A test system must not interact with an operational system</li>
<li>Use of address lists instead of broadcasts for name resolution and server
beacons</li>
<li>Control system occupies multiple IP subnets</li>
<li>Nonstandard client disconnect time outs or server beacon intervals</li>
<li>Specify the local time zone</li>
<li>Transport of large arrays</li>
</ul>
<h3><a name="EPICS">EPICS Environment Variables</a></h3>
<p>All Channel Access (CA) configuration occurs through EPICS environment
variables. When searching for an EPICS environment variable EPICS first looks
in the environment using the ANSI C getenv() call. If no matching variable
exists then the default specified in the EPICS build system configuration files
is used.</p>
<table cellspacing="1" cellpadding="1" width="75%" border="1">
<tbody>
<tr>
<th>Name</th>
<th>Range</th>
<th>Default</th>
</tr>
<tr>
<td>EPICS_CA_ADDR_LIST</td>
<td>{N.N.N.N N.N.N.N:P ...}</td>
<td>&lt;none&gt;</td>
</tr>
<tr>
<td>EPICS_CA_AUTO_ADDR_LIST</td>
<td>{YES, NO}</td>
<td>YES</td>
</tr>
<tr>
<td>EPICS_CA_CONN_TMO</td>
<td>r &gt; 0.1 seconds</td>
<td>30.0</td>
</tr>
<tr>
<td>EPICS_CA_BEACON_PERIOD</td>
<td>r &gt; 0.1 seconds</td>
<td>15.0</td>
</tr>
<tr>
<td>EPICS_CA_REPEATER_PORT</td>
<td>i &gt; 5000</td>
<td>5065</td>
</tr>
<tr>
<td>EPICS_CA_SERVER_PORT</td>
<td>i &gt; 5000</td>
<td>5064</td>
</tr>
<tr>
<td>EPICS_CA_MAX_ARRAY_BYTES</td>
<td>i &gt;= 16384</td>
<td>16384</td>
</tr>
<tr>
<td>EPICS_CA_MAX_SEARCH_PERIOD</td>
<td>r &gt; 60 seconds</td>
<td>300</td>
</tr>
<tr>
<td>EPICS_TS_MIN_WEST</td>
<td>-720 &lt; i &lt;720 minutes</td>
<td>360</td>
</tr>
</tbody>
</table>
<p>Environment variables are set differently depending on the command line
shell that is in use.</p>
<table border="1">
<tbody>
<tr>
<td>C shell</td>
<td>setenv EPICS_CA_ADDR_LIST  1.2.3.4</td>
</tr>
<tr>
<td>bash</td>
<td>export EPICS_CA_ADDR_LIST=1.2.3.4</td>
</tr>
<tr>
<td>vxWorks shell</td>
<td>putenv ( "EPICS_CA_ADDR_LIST =1.2.3.4" )</td>
</tr>
<tr>
<td>DOS command line</td>
<td>set EPICS_CA_ADDR_LIST=1.2.3.4</td>
</tr>
<tr>
<td>Windows NT / 2000 / XP</td>
<td>control panel / system / environment tab</td>
</tr>
</tbody>
</table>
<h3><a name="CA and Wide Area Networks"></a>CA and Wide Area Networks</h3>
<p>Normally in a local area network (LAN) environment CA discovers the address
of the host for an EPICS process variable by broadcasting frames containing a
list of channel names ( CA search messages ) and waiting for responses from the
servers that host the channels identified. Likewise CA clients efficiently
discover that CA servers have recently joined the LAN or disconnected from the
LAN by monitoring periodically broadcasted beacons sent out by the servers.
Since hardware broadcasting requires special hardware capabilities, we are
required to provide additional configuration information when EPICS is extended
to operate over a wide area network (WAN).</p>
<h3><a name="Network">IP Network Administration Background Information</a></h3>
<p>Channel Access is implemented using internet protocols (IP). IP addresses
are divided into host and network portions. The boundary between each portion
is determined by the IP netmask. Portions of the IP address corresponding to
zeros in the netmask specify the hosts address within an IP subnet. Portions of
the IP address corresponding to binary ones in the netmask specify the address
of a host's IP subnet. Normally the scope of a broadcasted frame will be
limited to one IP subnet. Addresses with the host address portion set to all
zeros or all ones are special. Modern IP kernel implementations reserve
destination addresses with the host portion set to all ones for the purpose of
addressing broadcasts to a particular subnet. In theory we can issue a
broadcast frame on any broadcast capable LAN within the interconnected internet
by specifying the proper subnet address combined with a host portion set to all
ones. In practice these "directed broadcasts" are frequently limited by the
default router configuration. The proper directed broadcast address required to
reach a particular host can be obtained by logging into that host and typing
the command required by your local operating environment. Ignore the loop back
interface and use the broadcast address associated with an interface connected
to a path through the network to your client. Typically there will be only one
Ethernet interface.</p>
<table border="1">
<tbody>
<tr>
<td>UNIX</td>
<td>ifconfig -a</td>
</tr>
<tr>
<td>vxWorks</td>
<td>ifShow</td>
</tr>
<tr>
<td>Windows</td>
<td>ipconfig</td>
</tr>
</tbody>
</table>
<p>IP ports are positive integers. The IP address, port number, and protocol
type uniquely identify the source and destination of a particular frame
transmitted between computers. Servers are typically addressed by a well known
port number. Clients are assigned a unique ephemeral port number during
initialization. IP ports below 1024 are reserved for servers that provide
standardized facilities such as mail or file transfer. Port number between 1024
and 5000 are typically reserved for ephemeral port number assignments.</p>
<h3><a name="port">IP port numbers</a></h3>
<p>The two default IP port numbers used by Channel Access may be reconfigured.
This might occur when a site decides to set up two or more completely
independent control systems that will share the same network. For instance, a
site might set up an operational control system and a test control system on
the same network. In this situation it is desirable for the test system and the
operational system to use identical PV names without fear of collision. A site
might also configure the CA port numbers because some other facility is already
using the default port numbers. The default Channel Access port numbers have
been registered with IANA.</p>
<table cellspacing="1" cellpadding="1" width="80%" border="1">
<col>
<tbody>
<tr>
<th>Purpose</th>
<th>Default</th>
<th>Environment Variable</th>
</tr>
<tr>
<td>CA Server</td>
<td>5064</td>
<td>EPICS_CA_SERVER_PORT</td>
</tr>
<tr>
<td>CA Beacons (sent to CA repeater daemon)</td>
<td>5065</td>
<td>EPICS_CA_REPEATER_PORT</td>
</tr>
</tbody>
</table>
<p>If a client needs to communicate with two servers that are residing at
different port numbers then an extended syntax may be used with the
EPICS_CA_ADDR_LIST environment variable. See <a href="#Environmen">WAN
Environment</a> below.</p>
<h3><a name="Environmen">WAN Environment</a></h3>
<p>When the CA client library connects a channel it must first determine the IP
address of the server the channels Process Variable resides on. To accomplish
this the client sends name resolution (search) requests to a list of server
destination addresses. These server destination addresses can be IP unicast
addresses (individual host addresses) or IP broadcast addresses. Each name
resolution (search) request contains a list of Process Variable names.If one of
the servers reachable by this address list knows the IP address of a CA server
that can service one or more of the specified Process Variables, then it sends
back a response containing the server's IP address and port number.</p>
<p>During initialization CA builds the list of server destination addresses
used when sending CA client name resolution (search) requests. This table is
initialized by introspecting the network interfaces attached to the host. For
each interface found that is attached to a broadcast capable IP subnet, the
broadcast address of that subnet is added to the list. For each point to point
interface found, the destination address of that link is added to the list.
This automatic server address list initialization can be disabled if the EPICS
environment variable "EPICS_CA_AUTO_ADDR_LIST" exists and its value is either
of "no" or "NO". The typical default is to enable network interface
introspection driven initialization with "EPICS_CA_AUTO_ADDR_LIST" set to "YES"
or "yes".</p>
<p>Following network interface introspection, any IP addresses specified in the
EPICS environment variable EPICS_CA_ADDR_LIST are added to the list of
destination addresses for CA client name resolution requests. In an EPICS
system crossing multiple subnets the EPICS_CA_ADDR_LIST must be set so that CA
name resolution ( search requests ) frames pass from CA clients to the targeted
CA servers unless a CA proxy (gateway) is installed. The addresses in
EPICS_CA_ADDR_LIST may be dotted IP addresses or host names if the local OS has
support for host name to IP address translation. When multiple names are added
to EPICS_CA_ADDR_LIST they must be separated by white space. There is no
requirement that the addresses specified in the EPICS_CA_ADDR_LIST be a
broadcast addresses, but this will often be the most convenient choice.</p>
<table border="1">
<tbody>
<tr>
<td>C shell</td>
<td>setenv EPICS_CA_ADDR_LIST "1.2.3.255 8.9.10.255"</td>
</tr>
<tr>
<td>bash</td>
<td>export EPICS_CA_ADDR_LIST="1.2.3.255 8.9.10.255"</td>
</tr>
<tr>
<td>vxWorks</td>
<td>putenv ( "EPICS_CA_ADDR_LIST=1.2.3.255 8.9.10.255" )</td>
</tr>
</tbody>
</table>
<p>If a client needs to communicate with two servers that are residing at
different port numbers then an extended syntax may be used with the
EPICS_CA_ADDR_LIST environment variable. Each host name or IP address in the
EPICS_CA_ADDR_LIST may be immediately followed by a colon and an IP port number
without intervening whitespace. Entries that do not specify a port number will
default to EPICS_CA_SERVER_PORT.</p>
<table border="1">
<tbody>
<tr>
<td>C shell</td>
<td>setenv EPICS_CA_ADDR_LIST "1.2.3.255 8.9.10.255:10000"</td>
</tr>
</tbody>
</table>
<h4><a name="Routing">Routing Restrictions on vxWorks Systems</a></h4>
<p>Frequently vxWorks systems boot by default with routes limiting access only
to the local subnet. If a EPICS system is operating in a WAN environment it may
be necessary to configure routes into the vxWorks system which enable a vxWorks
based CA server to respond to requests originating outside it's subnet. These
routing restrictions can also apply to vxWorks base CA clients communicating
with off subnet servers. An EPICS system manager can implement an rudimentary,
but robust, form of access control for a particular host by not providing
routes in that host that reach outside of a limited set of subnets. See
"routeLib" in the vxWorks reference manual.</p>
<h3><a name="Disconnect">Disconnect Time Out Interval</a></h3>
<p>If the CA client library does not see a beacon from a server that it is
connected to for EPICS_CA_CONN_TMO seconds then an state-of-health message is
sent to the server over TCP/IP. If this state-of-health message isn't promptly
replied to then the client library will conclude that channels communicating
with the server are no longer responsive and inform the CA client side
application via function callbacks. The parameter EPICS_CA_CONN_TMO is
specified in floating point seconds. The default is typically 30 seconds. For
efficient operation it is recommended that EPICS_CA_CONN_TMO be set to no less
than twice the value specified for EPICS_CA_BEACON_PERIOD.</p>
<p>Prior to EPICS R3.14.5 an unresponsive server implied an immediate TCP
circuit disconnect, immediate resumption of UDP based search requests, and
immediate attempts to reconnect. There was concern about excessive levels of
additional activity when servers are operated close to the edge of resource
limitations. Therefore with version R3.14.5 and greater the CA client library
continues to inform client side applications when channels are unresponsive,
but does not immediately disconnect the TCP circuit. Instead the CA client
library postpones circuit shutdown until receiving indication of circuit
disconnect from the IP kernel. This can occur either because a server is
restarted or because the IP kernel's internal TCP circuit inactivity keep alive
timer has expired after a typically long duration (as is appropriate for IP
based systems that need to avoid thrashing during periods of excessive load).
The net result is less search and TCP circuit setup and shutdown activity
suring periods of excessive load.</p>
<h3><a name="Dynamic">Dynamic Changes in the CA Client Library Search
Interval</a></h3>
<p>The CA client library will continuously attempt to connect any CA channels
that an application has created until it is successful. The library
periodically queries the server destination address list described above with
name resolution requests for any unresolved channels. Since this address list
frequently contains broadcast addresses, and because nonexistent process
variable names are frequently configured, or servers may be temporarily
unavailable, then it is necessary for the CA client library internals to
carefully schedule these requests in time to avoid introducing excessive load
on the network and the servers.</p>
<p>When the CA client library has many channels to connect, and most of its
name resolution requests are responded to, then it sends name resolution
requests at an interval that is twice the estimated round trip interval for the
set of servers responding, or at the minimum delay quantum for the operating
system - whichever is greater. The number of UDP frames per interval is also
dynamically adjusted based on the past success rates.</p>
<p>If a name resolution request is not responded to, then the client library
doubles the delay between name resolution attempts and reduces the number of
requests per interval. The maximum delay between attempts is limited by
EPICS_CA_MAX_SEARCH_PERIOD (see <a href="#Configurin3">Configuring the Maximum
Search Period</a>). Note however that prior to R3.14.7, if the client library
did not receive any responses over a long interval it stoped sending name
resolution attempts altogether until a beacon anomaly was detected (see
below).</p>
<p>The CA client library continually estimates the beacon period of all server
beacons received. If a particular server's beacon period becomes significantly
shorter or longer then the client is said to detect a beacon anomaly. The
library boosts the search interval for unresolved channels when a beacon
anomaly is seen or when <em>any</em> successful search response is received,
but with a longer initial interval between requests than is used when the
application creates a channel. Creation of a new channel does <em>not</em>
(starting with EPICS R3.14.7) change the interval used when searching for
preexisting unresolved channels. The program "casw" prints a message on
standard out for each CA client beacon anomaly detect event.</p>
<p>See also <a href="#Client1">When a Client Does not See the Server's
Beacon</a>.</p>
<h3><a name="Configurin3" id="Configurin3">Configuring the Maximum Search
Period</a></h3>
<p>The rate at which name resolution (search) requests are sent exponentially
backs off to a plateau rate. The value of this plateau has an impact on network
traffic because it determines the rate that clients search for channel names
that are miss-spelled or otherwise don't exist in a server. Furthermore, for
clients that are unable to see the beacon from a new server, the plateau rate
may also determine the maximum interval that the client will wait until
discovering a new server.</p>
<p>Starting with EPICS R3.14.7 this maximum search rate interval plateau in
seconds is determined by the EPICS_CA_MAX_SEARCH_PERIOD environment
variable.</p>
<p>See also <a href="#Client1">When a Client Does not See the Server's
Beacon</a>.</p>
<h3><a name="Repeater">The CA Repeater</a></h3>
<p>When several client processes run on the same host it is not possible for
all of them to directly receive a copy of the server beacon messages when the
beacon messages are sent to unicast addresses, or when legacy IP kernels are
still in use. To avoid confusion over these restrictions a special UDP server,
the CA Repeater, is automatically spawned by the CA client library when it is
not found to be running. This program listens for server beacons sent to the
UDP port specified in the EPICS_CA_REPEATER_PORT parameter and fans any beacons
received out to any CA client program running on the same host that have
registered themselves with the CA Repeater. If the CA Repeater is not already
running on a workstation, then the "caRepeater" program must be in your path
before using the CA client library for the first time.</p>
<p>If a host based IOC is run on the same workstation with standalone CA client
processes, then it is probably best to start the caRepeater process when the
workstation is booted. Otherwise it is possible for the standalone CA client
processes to become dependent on a CA repeater started within the confines of
the host based IOC. As long as the host based IOC continues to run there is
nothing wrong with this situation, but problems could arise if this host based
IOC process exits before the standalone client processes which are relying on
its CA repeater for services exit.</p>
<p>Since the repeater is intended to be shared by multiple clients then it
could be argued that it makes less sense to set up a CA repeater that listens
for beacons on only a subset of available network interfaces. In the worst case
situation the client library might see beacon anomalies from servers that it is
not interested in. Modifications to the CA repeater forcing it to listen only
on a subset of network interfaces might be considered for a future release if
there appear to be situations that require it.</p>
<h3><a name="Configurin">Configuring the Time Zone</a></h3>
<p><em>Note: Starting with EPICS R3.14 all of the libraries in the EPICS base
distribution rely on facilities built into the operating system to determine
the correct time zone. Nevertheless, several programs commonly used with EPICS
still use the original "tssubr" library and therefore they still rely on proper
configuration of EPICS_TS_MIN_WEST.</em></p>
<p>While the CA client library does not translate inbetween the local time and
the time zone independent internal storage of EPICS time stamps, many EPICS
client side applications call core EPICS libraries which provide these
services. To set the correct time zone users must compute the number of
positive minutes west of GMT (maximum 720 inclusive) or the negative number of
minutes east of GMT (minimum -720 inclusive). This integer value is then placed
in the variable EPICS_TS_MIN_WEST.</p>
<table cellspacing="1" cellpadding="1" width="75%" border="1">
<tbody>
<tr>
<th>Time Zone</th>
<th>EPICS_TS_MIN_WEST</th>
</tr>
<tr>
<td>USA Eastern</td>
<td>300</td>
</tr>
<tr>
<td>USA Central</td>
<td>360</td>
</tr>
<tr>
<td>USA Mountain</td>
<td>420</td>
</tr>
<tr>
<td>USA Pacific</td>
<td>480</td>
</tr>
<tr>
<td>Alaska</td>
<td>540</td>
</tr>
<tr>
<td>Hawaii</td>
<td>600</td>
</tr>
<tr>
<td>Japan</td>
<td>-540</td>
</tr>
<tr>
<td>China</td>
<td>-420</td>
</tr>
<tr>
<td>Germany</td>
<td>-120</td>
</tr>
<tr>
<td>United Kingdom</td>
<td>0</td>
</tr>
</tbody>
</table>
<h3><a name="Configurin1">Configuring the Maximum Array Size</a></h3>
<p>Starting with version R3.14 the environment variable
EPICS_CA_MAX_ARRAY_BYTES determines the size of the largest array that may pass
through CA. Prior to this version only arrays smaller than 16k bytes could be
transfered. The CA libraries maintains a free list of 16384 byte network
buffers that are used for ordinary communication. If EPICS_CA_MAX_ARRAY_BYTES 
is larger than 16384 then a second free list of larger data buffers is
established and used only after a client send its first large array request.</p>
<p>The CA client library uses EPICS_CA_MAX_ARRAY_BYTES to determines the
maximum array that it will send or receive. Likewise, the CA server uses
EPICS_CA_MAX_ARRAY_BYTES to determine the maximum array that it may send or
receive. The client does not influence the server's message size quotas and
visa versa. In fact the value of EPICS_CA_MAX_ARRAY_BYTES need not be the same
in the client and the server. If the server receives a request which is too
large to read or respond to in entirety then it sends an exception message to
the client. Likewise, if the CA client library receives a request to send an
array larger than EPICS_CA_MAX_ARRAY_BYTES it will return ECA_TOLARGE.</p>
<p>A common mistake is to correctly calculate the maximum datum size in bytes
by multiplying the number of elements by the size of a single element, but
neglect to add additional bytes for the compound data types (for example
DBR_GR_DOUBLE) commonly used by the more sophisticated client side
applications. <em>Based on this confusion, one could arrive at the conclusion
that EPICS_CA_MAX_ARRAY_BYTES might have been better named
EPICS_CA_MAX_DATUM_BYTES, or that the software should be changed internally to
round the users request up by the size of the maximum scalar datum (nothing has
been done to address this issue so far).</em></p>
<h3><a name="Configurin2">Configuring a CA Server</a></h3>
<table cellspacing="1" cellpadding="1" width="75%" border="1">
<tbody>
<tr>
<th>Name</th>
<th>Range</th>
<th>Default</th>
</tr>
<tr>
<td>EPICS_CAS_SERVER_PORT</td>
<td>i &gt; 5000</td>
<td>EPICS_CA_SERVER_PORT</td>
</tr>
<tr>
<td>EPICS_CAS_AUTO_BEACON_ADDR_LIST</td>
<td>{YES, NO}</td>
<td>EPICS_CA_AUTO_ADDR_LIST</td>
</tr>
<tr>
<td>EPICS_CAS_BEACON_ADDR_LIST</td>
<td>{N.N.N.NN.N.N.N:P...}</td>
<td>EPICS_CA_ADDR_LIST<sup>1</sup></td>
</tr>
<tr>
<td>EPICS_CAS_BEACON_PERIOD</td>
<td>r &gt; 0.1 seconds</td>
<td>EPICS_CA_BEACON_PERIOD</td>
</tr>
<tr>
<td>EPICS_CAS_BEACON_PORT</td>
<td>i &gt; 5000</td>
<td>EPICS_CA_REPEATER_PORT</td>
</tr>
<tr>
<td>EPICS_CAS_INTF_ADDR_LIST</td>
<td>{N.N.N.NN.N.N.N:P...}</td>
<td>&lt;none&gt;</td>
</tr>
<tr>
<td>EPICS_CAS_IGNORE_ADDR_LIST</td>
<td>{N.N.N.NN.N.N.N:P...}</td>
<td>&lt;none&gt;</td>
</tr>
</tbody>
</table>
<h4>Server Port</h4>
<p>The server configures its port number from the EPICS_CAS_SERVER_PORT
environment variable if it is specified. Otherwise the EPICS_CA_SERVER_PORT
environment variable determines the server's port number. Two servers can share
the same UDP port number on the same machine, but there are restrictions - see
a <a href="#Unicast">discussion of unicast addresses and two servers sharing
the same UDP port on the same host</a>.</p>
<h4>Server Beacons</h4>
<p>The EPICS_CAS_BEACON_PERIOD parameter determines the server's beacon period
and is specified in floating point seconds. The default is typically 15
seconds. See also <a href="#Disconnect">EPICS_CA_CONN_TMO</a> and <a
href="#Dynamic">Dynamic Changes in the CA Client Library Search
Interval</a>.</p>
<p>CA servers build a list of addresses to send beacons to during
initialization. If EPICS_CAS_AUTO_BEACON_ADDR_LIST has the value "YES" then the
beacon address list will be automatically configured to contain the broadcast
addresses of all LAN interfaces found in the host and the destination address
of all point-to-point interfaces found in the host. However, if the user also
defines EPICS_CAS_INTF_ADDR_LIST then beacon address list automatic
configuration is constrained to the network interfaces specified therein, and
therefore only the broadcast addresses of the specified LAN interfaces, and the
destination addresses of all specified point-to-point links, will be
automatically configured.</p>
<p>If EPICS_CAS_BEACON_ADDR_LIST is defined then its contents will be used to
augment any automatic configuration of the beacon address list. Individual
entries in EPICS_CAS_BEACON_ADDR_LIST may override the destination port number
if ":nnn" follows the host name or IP address there. Alternatively, when both
EPICS_CAS_BEACON_ADDR_LIST and EPICS_CAS_INTF_ADDR_LIST are not defined then
the contents of EPICS_CA_ADDR_LIST is used to augment the list. Otherwise, the
list is not augmented.</p>
<p>The EPICS_CAS_BEACON_PORT parameter specifies the destination port for
server beacons. The only exception to this occurs when ports are specified in
EPICS_CAS_BEACON_ADDR_LIST or possibly in EPICS_CA_ADDR_LIST. If
EPICS_CAS_BEACON_PORT is not specified then beacons are sent to the port
specified in EPICS_CA_REPEATER_PORT.</p>
<h4>Binding a Server to a Limited Set of Network Interfaces</h4>
<p>The parameter EPICS_CAS_INTF_ADDR_LIST allows a ca server to bind itself to,
and therefore accept messages only over, a limited set of the local host's
network interfaces (each specified by it's IP address). On UNIX systems type
"netstat -i" (type "ipconfig" on windows) to see a list of the local host's
network interfaces. Specifically, UDP search messages addressed to both the IP
addresses in EPICS_CAS_INTF_ADDR_LIST and also to the broadcast addresses of
the corresponding LAN interfaces will be accepted by the server. By default,
the CA server is accessible from all network interfaces configured into its
host. <em>In R3.14 and previous releases the CA server employed by iocCore does
not implemet this feature</em>.</p>
<h4>Ignoring Process Variable Name Resolution Requests From Certain Hosts</h4>
<p>Name resolution requests originating from any of the IP addresses specified
in the EPICS_CAS_IGNORE_ADDR_LIST parameter are not replied to.<em>In R3.14 and
previous releases the CA server employed by iocCore does not implemet this
feature.</em></p>
<h4>Client Configuration that also Applies to Servers</h4>
<p>See also <a href="#Configurin1">Configuring the Maximum Array Size</a>.</p>
<p>See also <a href="#Routing">Routing Restrictions on vxWorks Systems</a>.</p>
<h2><a name="Building" id="Building">Building an Application</a></h2>
<h3><a name="Required1" id="Required1">Required Header (.h) Files</a></h3>
<p>An application that uses the CA client library functions described in this
document will need to include the cadef.h header files as follows.</p>
<p><code>#include "cadef.h"</code></p>
<p>This header file is located at "&lt;EPICS base&gt;/include/". It includes
many other header files (operating system specific and otherwise), and
therefore the application must also specify "&lt;EPICS
base&gt;/include/os/&lt;arch&gt;" in its header file search path.</p>
<h3><a name="Required" id="Required">Required Libraries</a></h3>
<p>An application that uses the Channel Access Client Library functions
described in this document will need to link with the EPICS CA Client Library
and also the EPICS Common Library. The EPICS CA Client Library calls the EPICS
Common Library. The following table shows the names of these libraries on UNIX
and Windows systems.</p>
<table border="1">
<caption></caption>
<tbody>
<tr>
<th>
<div style="text-align: left">
</div>
</th>
<th>UNIX Object</th>
<th>UNIX Shareable</th>
<th>Windows Object</th>
<th>Windows Shareable</th>
</tr>
<tr>
<th style="text-align: left">EPICS CA Client Library</th>
<td>libca.a</td>
<td>libca.so</td>
<td>ca.lib</td>
<td>ca.dll</td>
</tr>
<tr>
<th>
<div style="text-align: left">
EPICS Common Library</div>
</th>
<td>libCom.a</td>
<td>libCom.so</td>
<td>Com.lib</td>
<td>Com.dll</td>
</tr>
</tbody>
</table>
<p></p>
<p>The above libraries are located in "&lt;EPICS
base&gt;/lib/&lt;architechture&gt;".</p>
<h3><a name="Compiler" id="Compiler">Compiler and System Specific Build
Options</a></h3>
<p>If you do not use the EPICS build environemnt (layered make files) then it
may be helpful to run one of the EPICS make files and watch the compile/link
lines. This may be the simplest way to capture the latest system and compiler
specific options required by your build environment. I have included some
snapshots of typical build lines below, but expect some risk of this
information becoming dated.</p>
<h4>Typical Linux Build Options</h4>
<p><code>/usr/bin/gcc -c -D_POSIX_C_SOURCE=199506L -D_POSIX_THREADS
-D_XOPEN_SOURCE=500 -DOSITHREAD_USE_DEFAULT_STACK -D_X86_ -DUNIX -D_BSD_SOURCE
-Dlinux -D_REENTRANT -ansi -O3 -Wall -I. -I.. -I../../../include/os/Linux
-I../../../include ../acctst.c</code></p>
<p><code>/usr/bin/g++ -o acctst
-L/home/user/epicsR3.14/epics/base/lib/linux-x86/
-Wl,-rpath,/mnt/bogart_home/hill/epicsR3.14/epics/base/lib/linux-x86
acctstMain.o acctst.o -lca -lCom</code></p>
<h4>Typical Solaris Build Options</h4>
<p><code>/opt/SUNWspro/bin/cc -c -D_POSIX_C_SOURCE=199506L -D_XOPEN_SOURCE=500
-DOSITHREAD_USE_DEFAULT_STACK -DUNIX -DSOLARIS=9 -mt -D__EXTENSIONS__ -Xc -v
-xO4 -I. -I.. -I./../../../include/os/solaris -I./../../../include
../acctst.c</code></p>
<p><code>/opt/SUNWspro/bin/CC -o acctst
-L/home/phoebus1/JHILL/epics/base/lib/solaris-sparc/ -mt -z ignore -z combreloc
-z lazyload -R/home/disk1/user/epics/base/lib/solaris-sparc acctstMain.o
acctst.o -lca -lCom</code></p>
<h4>Typical Windows Build Options</h4>
<p><code>cl -c /nologo /D__STDC__=0 /Ox /GL /W3 /w44355 /MD -I. -I..
-I..\\..\\..\\include\\os\\WIN32 -I..\\..\\..\\include ..\\acctst.c</code></p>
<p><code>link -nologo /LTCG /incremental:no /opt:ref /release /version:3.14
-out:acctst.exe acctstMain.obj acctst.obj
d:/user/R3.14.clean/epics/base/lib/WIN32-x86/ca.lib
d:/user/R3.14.clean/epics/base/lib/WIN32-x86/</code></p>
<h4>Typical vxWorks Build Options</h4>
<p><code>/usr/local/xcomp/ppc/bin/ccppc -c -D_POSIX_SOURCE -DCPU=PPC603
-DvxWorks -include /home/vx/tornado20/target/h/vxWorks.h -ansi -O3 -Wall
-mcpu=603 -mstrict-align -fno-builtin -I. -I.. -I../../../include/os/vxWorks
-I../../../include -I/home/vx/tornado20/target/h ../acctst.c</code></p>
<h4>Other Systems and Compilers</h4>
<p>Contributions gratefully accepted.</p>
<h2><a name="CommandUtils">Command Line Utilities</a></h2>
<h3><a name="acctst">acctst</a></h3>
<pre>acctst &lt;PV name&gt; [progress logging level] [channel duplication count]
[test repetition count] [enable preemptive callback]</pre>
<h4>Description</h4>
<p>Channel Access Client Library regression test.</p>
<p>The PV used with the test must be native type DBR_DOUBLE or DBR_FLOAT, and
modified only by acctst while the test is running. Therefore, periodically
scanned hardware attached analog input records do not work well. Test failure
is indicated if the program stops prior to printing "test complete". If
unspecified the progress logging level is zero, and no messages are printed
while the test is progressing. If unspecified, the channel duplication count is
20000. If unspecified, the test repetition count is once only. If unspecified,
preemptive callback is disabled.</p>
<h3><a name="catime">catime</a></h3>
<pre>catime &lt;PV name&gt; [channel count] [append number to pv name if true]</pre>
<h4>Description</h4>
<p>Channel Access Client Library performance test.</p>
<p>If unspecified, the channel count is 10000. If the "append number to pv name
if true" argument is specified and it is greater than zero then the channel
names in the test are numbered as follows.</p>
<p>&lt;PV name&gt;000000, &lt;PV name&gt;000001, ... &lt;PV name&gt;nnnnnn</p>
<h3><a name="casw">casw</a></h3>
<pre>casw [-i &lt;interest level&gt;]</pre>
<h4>Description</h4>
<p>CA server "beacon anomaly" logging.</p>
<p>CA server beacon anomalies occur when a new server joins the network, a
server is rebooted, network connectivity to a server is reestablished, or if a
server's CPU exits a CPU load saturated state.</p>
<p>CA clients with unresolved channels reset their search request scheduling
timers whenever they see a beacon anomaly.</p>
<p>This program can be used to detect situations where there are too many
beacon anomalies. IP routing configuration problems may result in false beacon
anomalies that might cause CA clients to use unnecessary additional network
bandwidth and server CPU load when searching for unresolved channels.</p>
<p>If there are no new CA servers appearing on the network, and network
connectivity remains constant, then casw should print no messages at all. At
higher interest levels the program prints a message for every beacon that is
received, and anomalous entries are flagged with a star.</p>
<h3><a name="caEventRat">caEventRate</a></h3>
<pre>caEventRate &lt;PV name&gt; [subscription count]</pre>
<h4>Description</h4>
<p>Connect to the specified PV, subscribe for monitor updates the specified
number of times (default once), and periodically log the current sampled event
rate, average event rate, and the standard deviation of the event rate in Hertz
to standard out.</p>
<h3><a name="ca_test">ca_test</a></h3>
<pre>ca_test &lt;PV name&gt; [value to be written]</pre>
<h4>Description</h4>
<p>If a value is specified it is written to the PV. Next, the current value of
the PV is converted to each of the many external data type that can be
specified at the CA client library interface, and each of these is formated and
then output to the console.</p>
<h2><a name="CommandTools">Command Line Tools</a></h2>
<h3><a name="caget">caget</a></h3>
<pre>caget [options] &lt;PV name&gt; ...</pre>
<h4>Description</h4>
<p>Get and print value for PV(s).</p>
<p>The values for one or multiple PVs are read and printed to stdout. The
DBR_... format in which the data is read, the output format, and a number of
details of how integer and float values are represented can be controlled using
command line options.</p>
<p>When getting multiple PVs, their order on the command line is retained in
the output.</p>
<table border="1">
<caption></caption>
<thead>
<tr>
<th>Option</th>
<th>Description</th>
</tr>
</thead>
<tbody>
<tr>
<td>-h</td>
<td>Print usage information</td>
</tr>
<tr>
<td></td>
<td><strong>CA options:</strong></td>
</tr>
<tr>
<td>-w &lt;sec&gt;</td>
<td>Wait time, specifies CA timeout, default is 1.0 second(s)</td>
</tr>
<tr>
<td>-c</td>
<td>Asynchronous get (use ca_get_callback and wait for completion)</td>
</tr>
<tr>
<td>-p &lt;prio&gt;</td>
<td>CA priority (0-99, default 0=lowest)</td>
</tr>
<tr>
<td></td>
<td><strong>Format and data type options:</strong></td>
</tr>
<tr>
<td></td>
<td>Default output format is "name value"</td>
</tr>
<tr>
<td>-t</td>
<td>Terse mode - print only value, without name</td>
</tr>
<tr>
<td>-a</td>
<td>Wide mode "name timestamp value stat sevr" (read PVs as
DBR_TIME_xxx)</td>
</tr>
<tr>
<td>-n</td>
<td>Print DBF_ENUM values as number (default are enum strings)</td>
</tr>
<tr>
<td>-d &lt;type&gt;</td>
<td>Request specific dbr type; use string (DBR_ prefix may be omitted)
<p>or number of one of the following types:</p>
<table border="1">
<tbody>
<tr>
<td>DBR_STRING</td>
<td>0</td>
<td>DBR_STS_FLOAT</td>
<td>9</td>
<td>DBR_TIME_LONG</td>
<td>19</td>
<td>DBR_CTRL_SHORT</td>
<td>29</td>
</tr>
<tr>
<td>DBR_INT</td>
<td>1</td>
<td>DBR_STS_ENUM</td>
<td>10</td>
<td>DBR_TIME_DOUBLE</td>
<td>20</td>
<td>DBR_CTRL_INT</td>
<td>29</td>
</tr>
<tr>
<td>DBR_SHORT</td>
<td>1</td>
<td>DBR_STS_CHAR</td>
<td>11</td>
<td>DBR_GR_STRING</td>
<td>21</td>
<td>DBR_CTRL_FLOAT</td>
<td>30</td>
</tr>
<tr>
<td>DBR_FLOAT</td>
<td>2</td>
<td>DBR_STS_LONG</td>
<td>12</td>
<td>DBR_GR_SHORT</td>
<td>22</td>
<td>DBR_CTRL_ENUM</td>
<td>31</td>
</tr>
<tr>
<td>DBR_ENUM</td>
<td>3</td>
<td>DBR_STS_DOUBLE</td>
<td>13</td>
<td>DBR_GR_INT</td>
<td>22</td>
<td>DBR_CTRL_CHAR</td>
<td>32</td>
</tr>
<tr>
<td>DBR_CHAR</td>
<td>4</td>
<td>DBR_TIME_STRING</td>
<td>14</td>
<td>DBR_GR_FLOAT</td>
<td>23</td>
<td>DBR_CTRL_LONG</td>
<td>33</td>
</tr>
<tr>
<td>DBR_LONG</td>
<td>5</td>
<td>DBR_TIME_INT</td>
<td>15</td>
<td>DBR_GR_ENUM</td>
<td>24</td>
<td>DBR_CTRL_DOUBLE</td>
<td>34</td>
</tr>
<tr>
<td>DBR_DOUBLE</td>
<td>6</td>
<td>DBR_TIME_SHORT</td>
<td>15</td>
<td>DBR_GR_CHAR</td>
<td>25</td>
<td>DBR_STSACK_STRING</td>
<td>37</td>
</tr>
<tr>
<td>DBR_STS_STRING</td>
<td>7</td>
<td>DBR_TIME_FLOAT</td>
<td>16</td>
<td>DBR_GR_LONG</td>
<td>26</td>
<td>DBR_CLASS_NAME</td>
<td>38</td>
</tr>
<tr>
<td>DBR_STS_SHORT</td>
<td>8</td>
<td>DBR_TIME_ENUM</td>
<td>17</td>
<td>DBR_GR_DOUBLE</td>
<td>27</td>
<td></td>
<td></td>
</tr>
<tr>
<td>DBR_STS_INT</td>
<td>8</td>
<td>DBR_TIME_CHAR</td>
<td>18</td>
<td>DBR_CTRL_STRING</td>
<td>28</td>
<td></td>
<td></td>
</tr>
</tbody>
</table>
</td>
</tr>
<tr>
<td></td>
<td><strong>Arrays:</strong></td>
</tr>
<tr>
<td></td>
<td>Value format: Print number of requested values, then list of
values</td>
</tr>
<tr>
<td>Default:</td>
<td>Print all values</td>
</tr>
<tr>
<td>-# &lt;count&gt;</td>
<td>Print first &lt;count&gt; elements of an array</td>
</tr>
<tr>
<td>-S</td>
<td>Print array of char as a string (long string)</td>
</tr>
<tr>
<td></td>
<td><strong>Floating point type format:</strong></td>
</tr>
<tr>
<td>Default:</td>
<td>Use %g format</td>
</tr>
<tr>
<td>-e &lt;nr&gt;</td>
<td>Use %e format, with &lt;nr&gt; digits after the decimal point</td>
</tr>
<tr>
<td>-f &lt;nr&gt;</td>
<td>Use %f format, with &lt;nr&gt; digits after the decimal point</td>
</tr>
<tr>
<td>-g &lt;nr&gt;</td>
<td>Use %g format, with &lt;nr&gt; digits after the decimal point</td>
</tr>
<tr>
<td>-s</td>
<td>Get value as string (may honour server-side precision)</td>
</tr>
<tr>
<td>-lx</td>
<td>Round to long integer and print as hex number</td>
</tr>
<tr>
<td>-lo</td>
<td>Round to long integer and print as octal number</td>
</tr>
<tr>
<td>-lb</td>
<td>Round to long integer and print as binary number</td>
</tr>
<tr>
<td></td>
<td><strong>Integer number format:</strong></td>
</tr>
<tr>
<td>Default:</td>
<td>Print as decimal number</td>
</tr>
<tr>
<td>-0x</td>
<td>Print as hex number</td>
</tr>
<tr>
<td>-0o</td>
<td>Print as octal number</td>
</tr>
<tr>
<td>-0b</td>
<td>Print as binary number</td>
</tr>
</tbody>
</table>
<h3><a name="camonitor">camonitor</a></h3>
<pre>camonitor [options] &lt;PV name&gt; ...</pre>
<h4>Description</h4>
<p>Subscribe to and print value updates for PV(s).</p>
<table border="1">
<caption></caption>
<thead>
<tr>
<th>Option</th>
<th>Description</th>
</tr>
</thead>
<tbody>
<tr>
<td>-h</td>
<td>Print usage information</td>
</tr>
<tr>
<td></td>
<td><strong>CA options:</strong></td>
</tr>
<tr>
<td>-w &lt;sec&gt;</td>
<td>Wait time, specifies CA timeout, default is 1.0 second(s)</td>
</tr>
<tr>
<td>-m &lt;mask&gt;</td>
<td>Specify CA event mask to use, with &lt;mask&gt; being any combination
of 'v' (value), 'a' (alarm), 'l' (log), 'p' (property). Default: va</td>
</tr>
<tr>
<td>-p &lt;prio&gt;</td>
<td>CA priority (0-99, default 0=lowest)</td>
</tr>
<tr>
<td></td>
<td><strong>Timestamps:</strong></td>
</tr>
<tr>
<td>Default:</td>
<td>Print absolute timestamps (as reported by CA server)</td>
</tr>
<tr>
<td>-t &lt;key&gt;</td>
<td>Specify timestamp source(s) and type, with &lt;key&gt; containing<br>
's' = CA server (remote) timestamps<br>
'c' = CA client (local) timestamps (shown in '()'s)<br>
'n' = no timestamps<br>
'r' = relative timestamps (time elapsed since start of program)<br>
'i' = incremental timestamps (time elapsed since last update)<br>
'I' = incremental timestamps (time elapsed since last update, by
channel)</td>
</tr>
<tr>
<td></td>
<td><strong>Enum Format:</strong></td>
</tr>
<tr>
<td>-n</td>
<td>Print DBF_ENUM values as number (default are enum strings)</td>
</tr>
<tr>
<td></td>
<td><strong>Arrays:</strong></td>
</tr>
<tr>
<td></td>
<td>Value format: Print number of requested values, then list of
values</td>
</tr>
<tr>
<td>Default:</td>
<td>Print all values</td>
</tr>
<tr>
<td>-# &lt;count&gt;</td>
<td>Print first &lt;count&gt; elements of an array</td>
</tr>
<tr>
<td>-S</td>
<td>Print array of char as a string (long string)</td>
</tr>
<tr>
<td></td>
<td><strong>Floating point type format:</strong></td>
</tr>
<tr>
<td>Default:</td>
<td>Use %g format</td>
</tr>
<tr>
<td>-e &lt;nr&gt;</td>
<td>Use %e format, with &lt;nr&gt; digits after the decimal point</td>
</tr>
<tr>
<td>-f &lt;nr&gt;</td>
<td>Use %f format, with &lt;nr&gt; digits after the decimal point</td>
</tr>
<tr>
<td>-g &lt;nr&gt;</td>
<td>Use %g format, with &lt;nr&gt; digits after the decimal point</td>
</tr>
<tr>
<td>-s</td>
<td>Get value as string (may honour server-side precision)</td>
</tr>
<tr>
<td>-lx</td>
<td>Round to long integer and print as hex number</td>
</tr>
<tr>
<td>-lo</td>
<td>Round to long integer and print as octal number</td>
</tr>
<tr>
<td>-lb</td>
<td>Round to long integer and print as binary number</td>
</tr>
<tr>
<td></td>
<td><strong>Integer number format:</strong></td>
</tr>
<tr>
<td>Default:</td>
<td>Print as decimal number</td>
</tr>
<tr>
<td>-0x</td>
<td>Print as hex number</td>
</tr>
<tr>
<td>-0o</td>
<td>Print as octal number</td>
</tr>
<tr>
<td>-0b</td>
<td>Print as binary number</td>
</tr>
</tbody>
</table>
<h3><a name="caput">caput</a></h3>
<pre>caput [options] &lt;PV name&gt; &lt;value&gt;
caput -a [options] &lt;PV name&gt; &lt;no of elements&gt; &lt;value&gt; ...</pre>
<h4>Description</h4>
<p>Put value to a PV.</p>
<p>The specified value is written to the PV (as a string). The PV value is read
before and after the write operation and printed as "Old" and "new" values on
stdout.</p>
<p>The array variant writes an array to the specified PV. The first numeric
argument specifying the number of array elements is kept for compatibility with
the array data format of caget - the actual number of values specified on the
command line is used.</p>
<table border="1">
<caption></caption>
<thead>
<tr>
<th>Option</th>
<th>Description</th>
</tr>
</thead>
<tbody>
<tr>
<td>-h</td>
<td>Print usage information</td>
</tr>
<tr>
<td></td>
<td><strong>CA options:</strong></td>
</tr>
<tr>
<td>-w &lt;sec&gt;</td>
<td>Wait time, specifies CA timeout, default is 1.0 second(s)</td>
</tr>
<tr>
<td>-c</td>
<td>Asynchronous put (use ca_put_callback and wait for completion)</td>
</tr>
<tr>
<td>-p &lt;prio&gt;</td>
<td>CA priority (0-99, default 0=lowest)</td>
</tr>
<tr>
<td></td>
<td><strong>Format options:</strong></td>
</tr>
<tr>
<td>-t</td>
<td>Terse mode - print only sucessfully written value, without name</td>
</tr>
<tr>
<td></td>
<td><strong>Enum Format:</strong></td>
</tr>
<tr>
<td></td>
<td>Auto - try value as ENUM string, then as index number</td>
</tr>
<tr>
<td>-n</td>
<td>Force interpretation of values as numbers</td>
</tr>
<tr>
<td>-s</td>
<td>Force interpretation of values as strings</td>
</tr>
<tr>
<td></td>
<td><strong>Arrays:</strong></td>
</tr>
<tr>
<td>-a</td>
<td>Put array data</td>
</tr>
<tr>
<td></td>
<td>Value format: Print number of requested values, then list of
values</td>
</tr>
<tr>
<td>-S</td>
<td>Put string as an array of char (long string)</td>
</tr>
</tbody>
</table>
<h3><a name="cainfo">cainfo</a></h3>
<pre>cainfo [options] &lt;PV name&gt; ...</pre>
<h4>Description</h4>
<p>Get and print channel and connection information for PV(s).</p>
<p>All available Channel Access related information about PV(s) is printed to
stdout.</p>
<p>The -s option allows to specify an interest level for calling Channel
Access' internal report function ca_client_status(), that prints lots of
internal informations on stdout, including environment settings, used CA ports
etc.</p>
<table border="1">
<caption></caption>
<thead>
<tr>
<th>Option</th>
<th>Description</th>
</tr>
</thead>
<tbody>
<tr>
<td>-h</td>
<td>Print usage information</td>
</tr>
<tr>
<td></td>
<td><strong>CA options:</strong></td>
</tr>
<tr>
<td>-w &lt;sec&gt;</td>
<td>Wait time, specifies CA timeout, default is 1.0 second(s)</td>
</tr>
<tr>
<td>-s &lt;level&gt;</td>
<td>Call ca_client_status with the specified interest level</td>
</tr>
<tr>
<td>-p &lt;prio&gt;</td>
<td>CA priority (0-99, default 0=lowest)</td>
</tr>
</tbody>
</table>
<h3><a name="excas" id="excas">excas</a></h3>
<p>excas [options]</p>
<p>This is an example CA server that is sometimes used for testing purposes. An
example server can be created with the makeBaseApp perl script, as descibed in
the application Developer's Guide.</p>
<table border="1">
<col>
<col>
<tbody>
<tr>
<th>Option</th>
<th>Description</th>
</tr>
<tr>
<td>-d &lt;uuuu&gt;</td>
<td>set level uuuu for debug messages, where uuuu is an positive integer
number</td>
</tr>
<tr>
<td>-p &lt;aaaa&gt;</td>
<td>prefix all of the PV names below with aaaa changing, for example, the
name of "bill" to "xyz:bill"</td>
</tr>
<tr>
<td>-t &lt;n.n&gt;</td>
<td>set execution time where n.n is a positive real number</td>
</tr>
<tr>
<td>-c &lt;uuuu&gt;</td>
<td>set the numbered alias count</td>
</tr>
<tr>
<td>-s &lt;nnn&gt;</td>
<td>the default, nnn is one, enables periodic scanning of the PV
replacing the PV with its value added with a small random change, when
nnn is zero it turns off this type of periodic scanning </td>
</tr>
<tr>
<td>-ss &lt;nnn&gt;</td>
<td>the default, nnn is one, enables synchronous scanning, and if nnn is
zero it turns on asynchronous scanning</td>
</tr>
<tr>
<td>-ad &lt;n.n&gt;</td>
<td>set the delay before asynchronous operations complete (defaults to
0.1 seconds)</td>
</tr>
<tr>
<td>-an &lt;nnn&gt;</td>
<td>set the maximum number of simultaneous asynchronous operations
(defaults to 1000)</td>
</tr>
</tbody>
</table>
<p>The example server has a compile time fixed set of example variables.</p>
<table border="1">
<col>
<col>
<col>
<col>
<col>
<col>
<col>
<tbody>
<tr>
<th>Process Variable Name</th>
<th>Number of Elements</th>
<th>IO Type</th>
<th>Data Type</th>
<th>High Limit</th>
<th>Low Limit</th>
<th>Scan Period</th>
</tr>
<tr>
<td>jane</td>
<td>1</td>
<td>Synchronous</td>
<td>float point, 64 bits</td>
<td>10.0</td>
<td>0.0</td>
<td>0.1 Seconds, random noise changes</td>
</tr>
<tr>
<td>fred</td>
<td>1</td>
<td>Synchronous</td>
<td>float point, 64 bits</td>
<td>10.0</td>
<td>-10.0</td>
<td>2.0 Seconds, random noise changes</td>
</tr>
<tr>
<td>janet</td>
<td>1</td>
<td>Asynchronous</td>
<td>float point, 64 bits</td>
<td>10.0</td>
<td>0.0</td>
<td>0.1 Seconds, random noise changes</td>
</tr>
<tr>
<td>freddy</td>
<td>1</td>
<td>Asynchronous</td>
<td>float point, 64 bits</td>
<td>10.0</td>
<td>-10.0</td>
<td>2.0 Seconds, random noise changes</td>
</tr>
<tr>
<td>alan</td>
<td>100</td>
<td>Synchronous</td>
<td>float point, 64 bits</td>
<td>10.0</td>
<td>-10.0</td>
<td>2.0 Seconds, random noise changes</td>
</tr>
<tr>
<td>albert</td>
<td>1000</td>
<td>Synchronous</td>
<td>float point, 64 bits</td>
<td>10.0</td>
<td>-10.0</td>
<td>20.0 Seconds, random noise changes</td>
</tr>
<tr>
<td>boot</td>
<td>1</td>
<td>Synchronous</td>
<td>enumerated, 16 bits</td>
<td>10.0</td>
<td>-10.0</td>
<td>changed only by client</td>
</tr>
<tr>
<td>booty</td>
<td>1</td>
<td>Asynchronous</td>
<td>enumerated, 16 bits</td>
<td>10.0</td>
<td>-10.0</td>
<td>1.0 Seconds, random noise changes</td>
</tr>
<tr>
<td>bill</td>
<td>1</td>
<td>Synchronous</td>
<td>float point, 64 bits</td>
<td>10.0</td>
<td>-10.0</td>
<td>changed only by client</td>
</tr>
<tr>
<td>billy</td>
<td>1</td>
<td>Asynchronous</td>
<td>float point, 64 bits</td>
<td>10.0</td>
<td>-10.0</td>
<td>changed only by client</td>
</tr>
<tr>
<td>bloaty</td>
<td>100000</td>
<td>Synchronous</td>
<td>float point, 64 bits</td>
<td>10.0</td>
<td>-10.0</td>
<td>changed only by client</td>
</tr>
</tbody>
</table>
<h4>Bugs</h4>
<p>Not all of the options listed above have been tested recently.</p>
<h2><span style="width: auto;"><a
name="Troublesho">Troubleshooting</a></span></h2>
<h3><a name="When">When Clients Do Not Connect to Their Server</a></h3>
<h4><a name="Broadcast">Client and Server Broadcast Addresses Dont
Match</a></h4>
<p>Verify that the broadcast addresses are identical on the server's host and
on the client's host. This can be checked on UNIX with "netstat -i" or
"ifconfig -a"; on vxWorks with ifShow; and on windows with ipconfig. It is
normal for the broadcast addresses to not be identical if the client and server
are not directly attached to the same IP subnet, and in this situation the
EPICS_CA_ADDR_LIST must be set. Otherwise, if the client and server are
intended to be on the same IP subnet, then the problem may be that the IP
netmask is incorrectly set in the network interface configuration. On most
operating systems, when the host's IP address is configured, the host's IP
subnet mask is also configured.</p>
<h4><a name="Client">Client Isn't Configured to Use the Server's Port</a></h4>
<p>Verify that the client and server are using the same UDP port. Check the
server's port by running "netstat -a | grep nnn" where nnn is the port number
configured in the client. If you do not set EPICS_CA_SERVER_PORT or
EPICS_CAS_SERVER_PORT then the default port will be 5064.</p>
<h4><a name="Unicast">Unicast Addresses in the EPICS_CA_ADDR_LIST Does not
Reliably Contact Servers Sharing the Same UDP Port on the Same Host</a></h4>
<p>Two servers can run on the same host with the same server port number, but
there are restrictions. If the host has a modern IP kernel it is possible to
have two or more servers share the same UDP port. It is not possible for these
servers to run on the same host using the same TCP port. If the CA server
library detects that a server is attempting to start on the same port as an
existing CA server then both servers will use the same UDP port, and the 2nd
server will be allocated an ephemeral TCP port. Clients can be configured to
use the same port number for both servers. They will locate the 2nd server via
the shared UDP port, and transparently connect to the 2nd server's ephemeral
TCP port. Be aware however that If there are two server's running on the same
host sharing the same UDP port then they will both receive UDP search requests
sent as broadcasts, but unfortunately (due to a weakness of most IP kernel
implementations) only one of the servers will typically receive UDP search
requests sent to unicast addresses (i.e. a single specific host's ip
address).</p>
<h4><a name="Client1">Client Does not See Server's Beacons</a></h4>
<p>Two conclusions deserve special emphasis. <em>First, if a client does not
see the server's beacons, then it will use additional network and server
resources sending periodic state-of-health messages.</em> <em>Second, if a
client does not see a newly introduced server's beacon, then it will take up to
EPICS_CA_MAX_SEARCH_PERIOD to find that newly introduced server.</em> Also,
starting with EPICS R3.14.7 the client library does <em>not</em> suspend
searching for a channel after 100 unsuccessful attempts until a beacon anomaly
is seen. Therefore, if the client library is from before version R3.14.7 of
EPICS and it timed out attempting to find a server whoose beacon cant be seen
by the client library then the client application might need to be restarted in
order to connect to this new beacon-out-of-range server. The typical situation
where a client would not see the server's beacon might be when the client isnt
on the same IP subnet as the server, and the client's EPICS_CA_ADDR_LIST was
modified to include a destination address for the server, but the server's
beacon address list was not modified so that it's beacons are received by the
client.</p>
<h4><a name="Server1">A Server's IP Address Was Changed</a></h4>
<p>When communication over a virtual circuit times out, then each channel
attached to the circuit enters a disconnected state and the disconnect callback
handler specified for the channel is called. However, the circuit is not
disconnected until TCP/IP's internal, typically long duration, keep alive timer
expires. The disconnected channels remain attached to the beleaguered circuit
and no attempt is made to search for, or to reestablish, a new circuit. If, at
some time in the future, the circuit becomes responsive again, then the
attached channels enter a connected state again and reconnect call back
handlers are called. Any monitor subscriptions that received an update message
while the channel was disconnected are also refreshed. If at any time the
library receives an indication from the operating system that a beleaguered
circuit has shutdown or was disconnected then the library will immediately
reattempt to find servers for each channel and connect circuits to them.</p>
<p>A well known negative side effect of the above behavior is that CA clients
will wait the full (typically long) duration of TCP/IP's internal keep alive
timer prior to reconnecting under the following scenario (all of the following
occur):</p>
<ul>
<li>An server's (IOC's) operating system crashes (or is abruptly turned off)
or a vxWorks system is stopped by any means</li>
<li>This operating system does not immediately reboot using the same IP
address</li>
<li>A duplicate of the server (IOC) is started appearing at a different IP
address</li>
</ul>
<p>It is unlikely that any rational organization will advocate the above
scenario in a production system. Nevertheless, there <em>are</em> opportunities
for users to become confused during control system <em>development</em>, but it
is felt that the robustness improvements justify isolated confusion during the
system integration and checkout activities where the above scenarios are most
likely to occur.</p>
<p>Contrast the above behavior with the CA client library behavior of releases
prior to R3.14.5 where the beleaguered circuit was immediately closed when
communication over it timed out. Any attached channels were immediately
searched for, and after successful search responses arrived then attempts were
made to build a new circuit. This behavior could result in undesirable resource
consumption resulting from periodic circuit setup and teardown overhead
(thrashing) during periods of CPU / network / IP kernel buffer congestion.</p>
<h3><a name="Requests" id="Requests">Put Requests Just Prior to Process
Termination Appear to be Ignored</a></h3>
<p>Short lived CA client applications that issue a CA put request and then
immediately exit the process (return from <code>main</code> or call
<code>exit</code>) may find that there request isn't executed. To guarantee
that the request is sent call <code>ca_flush</code> followed by
<code>ca_context_destroy</code> prior to terminating the process.</p>
<h3><a name="Problems">ENOBUFS Messages</a></h3>
<p>Many Berkley UNIX derived Internet Protocol (IP) kernels use a memory
management scheme with a fixed sized low level memory allocation quantum called
an "mbuf". Messages about "ENOBUFS" are an indication that your IP kernel is
running low on mbuf buffers. An IP kernel mbuf starvation situation may lead to
temporary IP communications stalls or reduced throughput. This issue has to
date been primarily associated with vxWorks systems where mbuf starvation on
earlier vxWorks versions is rumored to lead to permanent IP communications
stalls which are resolved only by a system reboot. IP kernels that use mbufs
frequently allow the initial and maximum number of mbufs to be configured.
Consult your OS's documentation for configuration procedures which vary between
OS and even between different versions of the same OS.</p>
<h4>Contributing Circumstances</h4>
<ul>
<li>The total number of connected clients is high. Each active socket
requires dedicated mbufs for protocol control blocks, and for any data that
might be pending in the operating system for transmission to Channel Access
or to the network at a given instant. If you increase the vxWorks limit on
the maximum number of file descriptors then it may also be necessary to
increase the size of the mbuf pool.</li>
</ul>
<ul>
<li>The server has multiple connections where the server's sustained event
(monitor subscription update) production rate is higher than the client's
or the network's sustained event consumption rate. This ties up a per
socket quota of mbufs for data that are pending transmission to the client
via the network. In particular, if there are multiple clients that
subscribe for monitor events but do not call ca_pend_event() or ca_poll()
to process their CA input queue, then a significant mbuf consuming backlog
can occur in the server.</li>
</ul>
<ul>
<li>The server does not get a chance to run (because some other higher
priority thread is running) and the CA clients are sending a high volume of
data over TCP or UDP. This ties up a quota of mbufs for each socket in the
server that isn't being reduced by the server's socket read system
calls.</li>
</ul>
<ul>
<li>The server has multiple stale connections. Stale connections occur when a
client is abruptly turned off or disconnected from the network, and an
internal "keepalive" timer has not yet expired for the virtual circuit in
the operating system, and therefore mbufs may be dedicated to unused
virtual circuits. This situation is made worse if there are active monitor
subscriptions associated with stale connections which will rapidly increase
the number of dedicated mbufs to the quota available for each circuit.</li>
<li>When sites switch to the vxWorks 5.4 IP kernel they frequently run into
network pool exhaustion problems. This may be because the original vxWorks
IP kernel expanded the network pool as needed at runtime while the new
kernel's pool is statically configured at compile time, and does
<em>not</em> expand as needed at runtime. Also, at certain sites problems
related to vxWorks network driver pool exhaustion have also been reported
(this can also result in ENOBUF diagnostic messages).</li>
</ul>
<h4>Related Diagnostics</h4>
<ul>
<li>The EPICS command "casr [interest level]" displays information about the
CA server and how many clients are connected.</li>
<li>The vxWorks command "inetstatShow" indicates how many bytes are pending
in mbufs and indirectly (based on the number of circuits listed) how many
mbuf based protocol control blocks have been consumed. The vxWorks commands
(availability depending on vxWorks version) mbufShow, netStackSysPoolShow,
and netStackDataPoolShow indicate how much space remains in the network
stack pool.</li>
<li>The RTEMS command "netstat [interest level]" displays network information
including mbuf consumption statistics.</li>
</ul>
<h3>Server Subscription Update Queuing</h3>
<p>If the subscription update producer in the server produces subscription
updates faster than the subscription update consumer in the client consumes
them, then events have to be discarded if the buffering in the server
isn&rsquo;t allowed to grow to an infinite size. This is a law of nature
&ndash; based on queuing theory of course.</p>
<p>What is done depends on the version of the CA server. All server versions
place quotas on the maximum number of subscription updates allowed on the
subscription update queue at any given time. If this limit is reached, an
intervening update is discarded in favor of a more recent update. Depending on
the version of the server, rapidly updating subscriptions are or are not
allowed to cannibalize the quotas of slow updating subscriptions in limited
ways. Nevertheless, there is always room on the queue for at least one update
for each subscription. This guarantees that the most recent update is always
sent.</p>
<p>Adding further complication, the CA client library also implements a
primitive type of flow control. If the client library sees that it is reading a
large number of messages one after another w/o intervening delay it knows that
it is not consuming events as fast as they are produced. In that situation it
sends a message telling the server to temporarily stop sending subscription
update messages. When the client catches up it sends another message asking the
server to resume with subscription updates. This prevents slow clients from
getting time warped, but also guarantees that intervening events are discarded
until the slow client catches up.</p>
<p>There is currently no message on the IOC&rsquo;s console when a particular
client is slow on the uptake. A message of this type used to exist many years
ago, but it was a source of confusion (and what we will call message noise) so
it was removed. </p>
<p>There is unfortunately no field in the protocol allowing the server to
indicate that an intervening subscription update was discarded. We should
probably add that capability in a future version. Such a feature would, for
example, be beneficial when tuning an archiver installation.</p>
<h2><a name="Function">Function Call Interface General Guidelines</a></h2>
<h3><a name="Flushing">Flushing and Blocking</a></h3>
<p>Significant performance gains can be realized when the CA client library
doesn't wait for a response to return from the server after each request. All
requests which require interaction with a CA server are accumulated (buffered)
and not forwarded to the IOC until one of ca_flush_io, ca_pend_io,
ca_pend_event, or ca_sg_pend are called allowing several operations to be
efficiently sent over the network together. Any process variable values written
into your program's variables by ca_get() should not be referenced by your
program until ECA_NORMAL has been received from ca_pend_io().</p>
<h3><a name="Status">Status Codes</a></h3>
<p>If successful, the routines described here return the status code
ECA_NORMAL. Unsuccessful status codes returned from the client library are
listed with each routine in this manual. Operations that appear to be valid to
the client can still fail in the server. Writing the string "off" to a floating
point field is an example of this type of error. If the server for a channel is
located in a different address space than the client then the ca_xxx()
operations that communicate with the server return status indicating the
validity of the request and whether it was successfully enqueued to the server,
but communication of completion status is deferred until a user callback is
called, or lacking that an exception handler is called. An error number and the
error's severity are embedded in CA status (error) constants. Applications
shouldn't test the success of a CA function call by checking to see if the
returned value is zero as is the UNIX convention. Below are several methods to
test CA function returns. See <a href="#ca_signal">ca_signal() and SEVCHK</a>
for more information on this topic.</p>
<pre><code>status = ca_XXXX();
SEVCHK( status, "ca_XXXX() returned failure status");
if ( status &amp; CA_M_SUCCESS ) {
printf ( "The requested ca_XXXX() operation didn't complete successfully");
}
if ( status != ECA_NORMAL ) {
printf("The requested ca_XXXX() operation didn't complete successfully because \"%s\"\n",
ca_message ( status ) );
}</code></pre>
<h3><a name="Channel">Channel Access Data Types</a></h3>
<p>CA channels form a virtual circuit between a process variable (PV) and a
client side application program. It is possible to connect a wide variety of
data sources into EPICS using the CA server library. When a CA channel
communicates with an EPICS Input Output Controller (IOC) then a field is a
specialization of a PV, and an EPICS record is a plug compatible function block
that contains fields, and the meta data below frequently are mapped onto
specific fields within the EPICS records by the EPICS record support (see the
EPICS Application Developer Guide).</p>
<p>Arguments of type chtype specifying the data type you wish to transfer. They
expect one of the set of DBR_XXXX data type codes defined in db_access.h. There
are data types for all of the C primitive types, and there are also compound (C
structure) types that include various process variable properties such as
units, limits, time stamp, or alarm status. The primitive C types follow a
naming convention where the C typedef dbr_xxxx_t corresponds to the DBR_XXXX
data type code. The compound (C structure) types follow a naming convention
where the C structure tag dbr_xxxx corresponds to the DBR_XXXX data type code.
The following tables provides more details on the structure of the CA data type
space. Since data addresses are passed to the CA client library as typeless
"void *" pointers then care should be taken to ensure that you have passed the
correct C data type corresponding to the DBR_XXXX type that you have specified.
Architecture independent types are provided in db_access.h to assist
programmers in writing portable code. For example "dbr_short_t" should be used
to send or receive type DBR_SHORT. Be aware that type name DBR_INT has been
deprecated in favor of the less confusing type name DBR_SHORT. In practice,
both the DBR_INT type code and the DBR_SHORT type code refer to a 16 bit
integer type, and are functionally equivalent.</p>
<table border="1">
<caption>Channel Access Primitive Data Types</caption>
<tbody>
<tr>
<th>CA Type Code</th>
<th>Primitive C Data Type</th>
<th>Data Size</th>
</tr>
<tr>
<td>DBR_CHAR</td>
<td>dbr_char_t</td>
<td>8 bit character</td>
</tr>
<tr>
<td>DBR_SHORT</td>
<td>dbr_short_t</td>
<td>16 bit integer</td>
</tr>
<tr>
<td>DBR_ENUM</td>
<td>dbr_enum_t</td>
<td>16 bit unsigned integer</td>
</tr>
<tr>
<td>DBR_LONG</td>
<td>dbr_long_t</td>
<td>32 bit signed integer</td>
</tr>
<tr>
<td>DBR_FLOAT</td>
<td>dbr_float_t</td>
<td>32 bit IEEE floating point</td>
</tr>
<tr>
<td>DBR_DOUBLE</td>
<td>dbr_double_t</td>
<td>64 bit IEEE floating point</td>
</tr>
<tr>
<td>DBR_STRING</td>
<td>dbr_string_t</td>
<td>40 character string</td>
</tr>
</tbody>
</table>
<table border="1">
<caption>Structure of the Channel Access Data Type Space</caption>
<tbody>
<tr>
<th>CA Type Code</th>
<th>Read / Write</th>
<th>Primitive C Data Type</th>
<th>Process Variable Properties</th>
</tr>
<tr>
<td>DBR_&lt;PRIMITIVE TYPE&gt;</td>
<td>RW</td>
<td>dbr_&lt;primitive type&gt;_t</td>
<td>value</td>
</tr>
<tr>
<td>DBR_STS_&lt;PRIMITIVE TYPE&gt;</td>
<td>R</td>
<td>struct dbr_sts_&lt;primitive type&gt;</td>
<td>value, alarm status, and alarm severity</td>
</tr>
<tr>
<td>DBR_TIME_&lt;PRIMITIVE TYPE&gt;</td>
<td>R</td>
<td>struct dbr_time_&lt;primitive type&gt;</td>
<td>value, alarm status, alarm severity, and time stamp</td>
</tr>
<tr>
<td>DBR_GR_&lt;PRIMITIVE TYPE&gt;</td>
<td>R</td>
<td>struct dbr_gr_&lt;primitive type&gt;</td>
<td>value, alarm status, alarm severity, units, display precision, and
graphic limits</td>
</tr>
<tr>
<td>DBR_CTRL_&lt;PRIMITIVE TYPE&gt;</td>
<td>R</td>
<td>struct dbr_ctrl_&lt;primitive type&gt;</td>
<td>value, alarm status, alarm severity, units, display precision,
graphic limits, and control limits</td>
</tr>
<tr>
<td>DBR_PUT_ACKT</td>
<td>W</td>
<td>dbr_put_ackt_t</td>
<td>Used for global alarm acknowledgement. Do transient alarms have to be
acknowledged? (0,1) means (no, yes).</td>
</tr>
<tr>
<td>DBR_PUT_ACKS</td>
<td>W</td>
<td>dbr_put_acks_t</td>
<td>Used for global alarm acknowledgement. The highest alarm severity to
acknowledge. If the current alarm severity is less then or equal to
this value the alarm is acknowledged.</td>
</tr>
<tr>
<td>DBR_STSACK_STRING</td>
<td>R</td>
<td>struct dbr_stsack_string</td>
<td>value, alarm status, alarm severity, ackt, ackv</td>
</tr>
<tr>
<td>DBR_CLASS_NAME</td>
<td>R</td>
<td>dbr_class_name_t</td>
<td>name of enclosing interface (name of the record if channel is
attached to EPICS run time database)</td>
</tr>
</tbody>
</table>
<p></p>
<p>Channel value arrays can also be included within the structured CA data
types. If more than one element is requested, then the individual elements can
be accessed in an application program by indexing a pointer to the value field
in the DBR_XXX structure. For example, the following code computes the sum of
the elements in a array process variable and prints its time stamp. The <a
href="#L6946">dbr_size_n</a> function can be used to determine the correct
number of bytes to reserve when there are more than one value field elements in
a structured CA data type.</p>
<pre><code>#include &lt;stdio.h&gt;
#include &lt;stdlib.h&gt;
#include "cadef.h"
int main ( int argc, char ** argv )
{
struct dbr_time_double * pTD;
const dbr_double_t * pValue;
unsigned nBytes;
unsigned elementCount;
char timeString[32];
unsigned i;
chid chan;
double sum;
int status;
if ( argc != 2 ) {
fprintf ( stderr, "usage: %s &lt;channel name&gt;", argv[0] );
return -1;
}
status = ca_create_channel ( argv[1], 0, 0, 0, &amp; chan );
SEVCHK ( status, "ca_create_channel()" );
status = ca_pend_io ( 15.0 );
if ( status != ECA_NORMAL ) {
fprintf ( stderr, "\"%s\" not found.\n", argv[1] );
return -1;
}
elementCount = ca_element_count ( chan );
nBytes = dbr_size_n ( DBR_TIME_DOUBLE, elementCount );
pTD = ( struct dbr_time_double * ) malloc ( nBytes );
if ( ! pTD ) {
fprintf ( stderr, "insufficient memory to complete request\n" );
return -1;
}
status = ca_array_get ( DBR_TIME_DOUBLE, elementCount, chan, pTD );
SEVCHK ( status, "ca_array_get()" );
status = ca_pend_io ( 15.0 );
if ( status != ECA_NORMAL ) {
fprintf ( stderr, "\"%s\" didnt return a value.\n", argv[1] );
return -1;
}
pValue = &amp; pTD-&gt;value;
sum = 0.0;
for ( i = 0; i &lt; elementCount; i++ ) {
sum += pValue[i];
}
epicsTimeToStrftime ( timeString, sizeof ( timeString ),
"%a %b %d %Y %H:%M:%S.%f", &amp; pTD-&gt;stamp );
printf ( "The sum of elements in %s at %s was %f\n",
argv[1], timeString, sum );
ca_clear_channel ( chan );
ca_task_exit ();
free ( pTD );
return 0;
}</code></pre>
<h3><a name="User">User Supplied Callback Functions</a></h3>
<p>Certain CA client initiated requests asynchronously execute an application
supplied call back in the client process when a response arrives. The functions
ca_put_callback, ca_get_callback, and ca_add_event all request notification of
asynchronous completion via this mechanism. The <code>event_handler_args
</code>structure is passed <em>by value</em> to the application supplied
callback. In this structure the <code>dbr</code> field is a void pointer to any
data that might be returned. The <code>s</code><code>tatus </code>field will be
set to one of the CA error codes in caerr.h and will indicate the status of the
operation performed in the IOC. If the status field isn't set to ECA_NORMAL or
data isn't normally returned from the operation (i.e. put call back) then you
should expect that the <code>dbr </code>field will be set to a nill pointer
(zero). The fields <code>usr</code>, <code>chid</code>, and <code>type</code>
are set to the values specified when the request was made by the application.
The "dbr" pointer, and any data that it points to, are valid only when
executing within the user's callback function.</p>
<pre><code>typedef struct event_handler_args {
void *usr; /* user argument supplied with request */
chanId chid; /* channel id */
long type; /* the type of the item returned */
long count; /* the element count of the item returned */
const void *dbr; /* a pointer to the item returned */
int status; /* ECA_XXX status of the requested op from the server */
} evargs;
void myCallback ( struct event_handler_args args )
{
if ( args.status != ECA_NORMAL ) {
}
if ( args.type == DBR_TIME_DOUBLE ) {
const struct dbr_time_double * pTD =
( const struct dbr_time_double * ) args.dbr;
}
}</code></pre>
<h3><a name="Channel1">Channel Access Exceptions</a></h3>
<p>When the server detects a failure, and there is no client call back function
attached to the request, then an exception handler is executed in the client.
The default exception handler prints a message on the console and exits if the
exception condition is severe. Certain internal exceptions within the CA client
library, and failures detected by the SEVCHK macro may also cause the exception
handler to be invoked. To modify this behavior see <a
href="#ca_add_exception_event">ca_add_exception_event()</a>.</p>
<h3><a name="Server">Server and Client Share the Same Address Space on The Same
Host</a></h3>
<p>If the Process Variable's server and it's client are colocated within the
same memory address space and the same host then the ca_xxx() operations bypass
the server and directly interact with the server tool component (commonly the
IOC's function block database). In this situation the ca_xxx() routines
frequently return the completion status of the requested operation directly to
the caller with no opportunity for asynchronous notification of failure via an
exception handler. Likewise, callbacks may be directly invoked by the CA
library functions that request them.</p>
<h3><a name="Arrays">Arrays</a></h3>
<p>For routines that require an argument specifying the number of array
elements, no more than the process variable's maximum native element count may
be requested. The process variable's maximum native element count is available
from ca_element_count() when the channel is connected. If less elements than
the process variable's native element count are requested the requested values
will be fetched beginning at element zero. By default CA limits the number of
elements in an array to be no more than approximately 16k divided by the size
of one element in the array. Starting with EPICS R3.14 the maximum array size
may be configured in the client and in the server.</p>
<h3><a name="Connection">Connection Management</a></h3>
<p>Application programs should assume that CA servers may be restarted, and
that network connectivity is transient. When you create a CA channel its
initial connection state will most commonly be disconnected. If the Process
Variable's server is available the library will immediately initiate the
necessary actions to make a connection with it. Otherwise, the client library
will monitor the state of servers on the network and connect or reconnect with
the process variable's server as it becomes available. After the channel
connects the application program can freely perform IO operations through the
channel, but should expect that the channel might disconnect at any time due to
network connectivity disruptions or server restarts.</p>
<p>Three methods can be used to determine if a channel is connected: the
application program might call <a href="#ca_state"><code>ca_state</code></a> to
obtain the current connection state, block in <code><a
href="#ca_pend_io">ca_pend_io</a></code> until the channel connects, or install
a connection callback handler when it calls <code><a
href="#ca_create_channel">ca_create_channel</a></code>. The <code><a
href="#ca_pend_io">ca_pend_io</a></code> approach is best suited to simple
command line programs with short runtime duration, and the connection callback
method is best suited to toolkit components with long runtime duration. Use of
<code><a href="#ca_state">ca_state</a> </code>is appropriate only in programs
that prefer to poll for connection state changes instead of opting for
asynchronous notification. The <code>ca_pend_io</code> function blocks only for
channels created specifying a nill connection handler callback function. The
user's connection state change function will be run immediately from within
<code><a href="#ca_create_channel">ca_create_channel</a> </code>if the CA
client and CA server are both hosted within the same address space (within the
same process).</p>
<h3><a name="Thread">Thread Safety and Preemptive Callback to User Code</a></h3>
<p>Starting with EPICS R3.14 the CA client libraries are fully thread safe on
all OS (in past releases the library was thread safe only on vxWorks). When the
client library is initialized the programmer may specify if preemptive call
back is enabled. Preemptive call back is disabled by default. If preemptive
call back is enabled then the user's call back functions might be called by
CA's auxiliary threads when the main initiating channel access thread is not
inside of a function in the channel access client library. Otherwise, the
user's call back functions will be called only when the main initiating channel
access thread is executing inside of the CA client library. When the CA client
library invokes a user's call back function it will always wait for the current
callback to complete prior to executing another call back function. Programmers
enabling preemptive callback should be familiar with using mutex locks to
create a reliable multi-threaded program.</p>
<p>To set up a traditional single threaded client you will need code like this
(see <a href="#ca_context_create">ca_context_create</a> and <a
href="#Client2">CA Client Contexts and Application Specific Auxiliary
Threads</a>) .</p>
<p><code>SEVCHK ( ca_context_create(ca_disable_preemptive_callback ),
"application pdq calling ca_context_create" );</code></p>
<p>To set up a preemptive callback enabled CA client context you will need code
like this (see <a href="#ca_context_create">ca_context_create</a> and <a
href="#Client2">CA Client Contexts and Application Specific Auxiliary
Threads</a>).</p>
<p><code>SEVCHK ( ca_context_create(ca_enable_preemptive_callback ),
"application pdq calling ca_context_create" );</code></p>
<h3><a name="Client2">CA Client Contexts and Application Specific Auxiliary
Threads</a></h3>
<p>It is often necessary for several CA client side tools running in the same
address space (process) to be independent of each other. For example, the
database CA links and the sequencer are designed to not use the same CA client
library threads, network circuits, and data structures. Each thread that calls
<a href="#ca_context_create">ca_context_create()</a> for the first time either
directly, or implicitly when calling any CA library function for the first
time, creates a CA client library context. A CA client library context contains
all of the threads, network circuits, and data structures required to connect
and communicate with the channels that a CA client application has created. The
priority of auxiliary threads spawned by the CA client library are at fixed
offsets from the priority of the thread that called <a
href="#ca_context_create">ca_context_create()</a>. An application specific
auxiliary thread can join a CA context by calling <a
href="#ca_attach_context">ca_attach_context()</a> using the CA context
identifier that was returned from <a
href="#ca_current_context">ca_current_context()</a> when it is called by the
thread that created the context which needs to be joined. A context which is to
be joined must be preemptive - it must be created using <a
href="#ca_context_create">ca_context_create(ca_enable_preemptive_callback)</a>.
It is not possible to attach a thread to a non-preemptive CA context created
explicitly <em>or implicitly</em> with
ca_create_context(ca_disable_preemptive_callback). Once a thread has joined
with a CA context it need only make ordinary ca_xxxx() library calls to use the
context.</p>
<p>A CA client library context can be shut down and cleaned up, after
destroying any channels or application specific threads that are attached to
it, by calling <a href="#ca_context_destroy">ca_context_destroy()</a>. The
context may be created and destroyed by different threads as long as they are
both part of the same context.</p>
<h3><a name="Polling">Polling the CA Client Library From Single Threaded
Applications</a></h3>
<p>If preemptive call back is not enabled, then for proper operation CA must
periodically be polled to take care of background activity. This requires that
your application must either wait in one of ca_pend_event(), ca_pend_io(), or
ca_sg_block() or alternatively it must call ca_poll() at least every 100
milli-seconds. In single threaded applications a file descriptor manager like
Xt or the interface described in fdManager.h can be used to monitor both mouse
clicks and also CA's file descriptors so that ca_poll() can be called
immediately when CA server messages arrives over the network.</p>
<h3><a name="Avoid">Avoid Emulating Bad Practices that May Still be
Common</a></h3>
<p>With the embryonic releases of EPICS it was a common practice to examine a
channel's connection state, its native type, and its native element count by
directly accessing fields in a structure using a pointer stored in type
<code>chid</code>. Likewise, a user private pointer in the per channel
structure was also commonly set by directly accessing fields in the channel
structure. A number of difficulties arise from this practice, which has long
since been deprecated. For example, prior to release 3.13 it was recognized
that transient changes in certain private fields in the per channel structure
would make it difficult to reliably test the channels connection state using
these private fields directly. Therefore, in release 3.13 the names of certain
fields were changed to discourage this practice. Starting with release 3.14
codes written this way will not compile. Codes intending to maintain the
highest degree of portability over a wide range of EPICS versions should be
especially careful. For example you should replace all instances off
<code>channel_id-&gt;count</code> with
<code>ca_element_count(channel_id)</code>. This approach should be reliable on
all versions of EPICS in use today. The construct <code>ca_puser(chid) =
xxxx</code> is particularly problematic. The best mechanisms for setting the
per channel private pointer will be to pass the user private pointer in when
creating the channel. This approach is implemented on all versions. Otherwise,
you can also use <code>ca_set_puser(CHID,PUSER)</code>, but this function is
available only after the first official (post beta) release of EPICS 3.13.</p>
<h3><a name="Calling">Calling CA Functions from the vxWorks Shell
Thread</a></h3>
<p>Calling CA functions from the vxWorks shell thread is a somewhat
questionable practice for the following reasons.</p>
<ul>
<li>The vxWorks shell thread runs at the very highest priority in the system
and therefore socket calls are made at a priority that is above the
priority of tNetTask &minus; a practice that has caused the WRS IP kernel
to get sick in the past. That symptom was observed some time ago, but we
don&rsquo;t know if WRS has fixed the problem.</li>
</ul>
<ul>
<li>The vxWorks shell thread runs at the very highest priority in the system
and therefore certain CA auxiliary threads will not get the priorities that
are requested for them. This might cause problems only when in a CPU
saturation situations.</li>
</ul>
<ul>
<li>If the code does not call ca_context_destroy (ca_task_exit in past
releases) then resources are left dangling.</li>
</ul>
<ul>
<li>In EPICS R3.13 the CA client library installed vxWorks task exit handlers
behaved strangely if CA functions were called from the vxWorks shell,
ca_task_exit() wasn&rsquo;t called, and the vxWorks shell restarted. In
EPICS R3.14 vxWorks task exit handlers are not installed and therefore
cleanup is solely the responsibility of the user. With EPICS R3.14 the user
must call ca_context_destroy or ca_task_exit to clean up on vxWorks. This
is the same behavior as on all other OS.</li>
</ul>
<h3><a name="Calling1" id="Calling1">Calling CA Functions from POSIX signal
handlers</a></h3>
<p>As you might expect, it isnt safe to call the CA client library from a POSIX
signal handler. Likewise, it isnt safe to call the CA client library from
interrupt context.</p>
<h2><a name="Function Call Reference"></a>Function Call Reference</h2>
<h3><code><a name="ca_context_create">ca_context_create()</a></code></h3>
<pre><code>#include &lt;cadef.h&gt;
enum ca_preemptive_callback_select
{ ca_disable_preemptive_callback, ca_enable_preemptive_callback };
int ca_context_create ( enum ca_preemptive_callback_select SELECT );</code></pre>
<h4>Description</h4>
<p>This function, or <a href="#ca_attach_context">ca_attach_context()</a>,
should be called once from each thread prior to making any of the other Channel
Access calls. If one of the above is not called before making other CA calls
then a non-preemptive context is created by default, and future attempts to
create a preemptive context for the current threads will fail.</p>
<p>If <code>ca_disable_preemptive_callback</code> is specified then additional
threads are <em>not </em>allowed to join the CA context using
ca_context_attach() because allowing other threads to join implies that CA
callbacks will be called preemptively from more than one thread.</p>
<h4>Arguments</h4>
<dl>
<dt><code>SELECT</code></dt>
<dd>This argument specifies if preemptive invocation of callback functions
is allowed. If so your callback functions might be called when the thread
that calls this routine is not executing in the CA client library. There
are two implications to consider. </dd>
<dd><p>First, if preemptive callback mode is enabled the developer must
provide mutual exclusion protection for his data structures. In this mode
it's possible for two threads to touch the application's data structures
at once: this might be the initializing thread (the thread that called
ca_context_create) and also a private thread created by the CA client
library for the purpose of receiving network messages and calling
callbacks. It might be prudent for developers who are unfamiliar with
mutual exclusion locking in a multi-threaded environment to specify
<code>ca_disable_preemptive_callback</code>. </p>
<p>Second, if preemptive callback mode is enabled the application is no
longer burdened with the necessity of periodically polling the CA client
library in order that it might take care of its background activities. If
<code>ca_enable_preemptive_callback</code> is specified then CA client
background activities, such as connection management, will proceed even
if the thread that calls this routine is not executing in the CA client
library. Furthermore, in preemptive callback mode callbacks might be
called with less latency because the library is not required to wait
until the initializing thread (the thread that called ca_context_create)
is executing within the CA client library.</p>
</dd>
</dl>
<h4>Returns</h4>
<p>ECA_NORMAL - Normal successful completion</p>
<p>ECA_ALLOCMEM - Failed, unable to allocate space in pool</p>
<p>ECA_NOTTHREADED - Current thread is already a member of a non-preemptive
callback CA context (possibly created implicitly)</p>
<h4>See Also</h4>
<p>ca_context_destroy()</p>
<h3><code><a name="ca_context_destroy">ca_context_destroy()</a></code></h3>
<pre>#include &lt;cadef.h&gt;
void ca_context_destroy();</pre>
<h4>Description</h4>
<p>Shut down the calling thread's channel access client context and free any
resources allocated. Detach the calling thread from any CA client context.</p>
<p>Any user-created threads that have attached themselves to the CA context
must stop using it prior to its being destroyed. A program running in an IOC
context must delete all of its channels prior to calling ca_context_destroy()
to avoid a crash.</p>
<p>A CA client application that calls epicsExit() <em>must</em> install an
EPICS exit handler that calls ca_context_destroy() only <em>after</em> first
calling ca_create_context(). This will guarantee that the EPICS exit handlers
get called in the correct order.</p>
<p>On many OS that execute programs in a process based environment the
resources used by the client library such as sockets and allocated memory are
automatically released by the system when the process exits and
ca_context_destroy() hasn't been called, but on light weight systems such as
vxWorks or RTEMS no cleanup occurs unless the application call
ca_context_destroy().</p>
<h4>Returns</h4>
<p>ECA_NORMAL - Normal successful completion</p>
<h4>See Also</h4>
<p><a>ca_context_create()</a></p>
<h3><a name="ca_create_channel"><code>ca_create_channel()</code></a></h3>
<pre><code>#include &lt;cadef.h&gt;
typedef void ( *pCallBack ) (
struct connection_handler_args );
int ca_create_channel
(
const char *PROCESS_VARIABLE_NAME,
caCh *USERFUNC,
void *PUSER,
capri priority,
chid *PCHID
);</code></pre>
<h4>Description</h4>
<p>This function creates a CA channel. The CA client library will attempt to
establish and maintain a virtual circuit between the caller's application and a
named process variable in a CA server. Each call to ca_create_channel allocates
resources in the CA client library and potentially also a CA server. The
function ca_clear_channel() is used to release these resources. If successful,
the routine writes a channel identifier into the user's variable of type
"chid". This identifier can be used with any channel access call that operates
on a channel.</p>
<p>The circuit may be initially connected or disconnected depending on the
state of the network and the location of the channel. A channel will only enter
a connected state after server's address is determined, and only if channel
access successfully establishes a virtual circuit through the network to the
server. Channel access routines that send a request to a server will return
ECA_DISCONNCHID if the channel is currently disconnected.</p>
<p>There are two ways to obtain asynchronous notification when a channel enters
a connected state.</p>
<ul>
<li>The first and simplest method requires that you call ca_pend_io(), and
wait for successful completion, prior to using a channel that was created
specifying a nil connection call back function pointer.</li>
<li>The second method requires that you register a connection handler by
supplying a valid connection callback function pointer. This connection
handler is called whenever the connection state of the channel changes. If
you have installed a connection handler then ca_pend_io() will <em>not</em>
block waiting for the channel to enter a connected state.</li>
</ul>
<p>The function ca_state(CHID) can be used to test the connection state of a
channel. Valid connections may be isolated from invalid ones with this function
if ca_pend_io() times out.</p>
<p>Due to the inherently transient nature of network connections the order of
connection call backs relative to the order that ca_create_channel() calls are
made by the application can't be guaranteed, and application programs may need
to be prepared for a connected channel to enter a disconnected state at any
time.</p>
<h4>Example</h4>
<p>See caExample.c in the example application created by makeBaseApp.pl.</p>
<h4>Arguments</h4>
<dl>
<dt><code>PROCESS_VARIABLE_NAME</code></dt>
<dd>A nil terminated process variable name string. EPICS process control
function block database variable names are of the form "&lt;record
name&gt;.&lt;field name&gt;". If the field name and the period separator
are omitted then the "VAL" field is implicit. For example "RFHV01" and
"RFHV01.VAL" reference the same EPICS process control function block
database variable.</dd>
</dl>
<dl>
<dt><code>USERFUNC</code></dt>
<dd>Optional address of the user's call back function to be run when the
connection state changes. Casual users of channel access may decide to
set this field to nil or 0 if they do not need to have a call back
function run in response to each connection state change event.
<p>The following structure is passed <em>by value </em>to the user's
connection connection callback function. The <code>op</code> field will
be set by the CA client library to <code>CA_OP_CONN_UP</code> when the
channel connects, and to <code>CA_OP_CONN_DOWN </code>when the channel
disconnects. See <code><a href="#ca_puser">ca_puser</a></code> if the
<code>PUSER </code>argument is required in your callback
handler<code>.</code></p>
<pre><code>struct ca_connection_handler_args {
chanId chid; /* channel id */
long op; /* one of CA_OP_CONN_UP or CA_OP_CONN_DOWN */
};</code></pre>
</dd>
</dl>
<dl>
<dt><code>PUSER</code></dt>
<dd>The value of this void pointer argument is retained in
storage associated with the specified channel. See the MACROS manual page
for reading and writing this field. Casual users of channel access may
wish to set this field to nil or 0.</dd>
</dl>
<dl>
<dt><code>PRIORITY</code></dt>
<dd>The priority level for dispatch within the server or network with 0
specifying the lowest dispatch priority and 99 the highest. This
parameter currently does not impact dispatch priorities within the
client, but this might change in the future. The abstract priority range
specified is mapped into an operating system specific range of priorities
within the server. This parameter is ignored if the server is running on
a network or operating system that does not have native support for
prioritized delivery or execution respectively. Specifying many different
priorities within the same program can increase resource consumption in
the client and the server because an independent virtual circuit, and
associated data structures, is created for each priority that is used on
a particular server.</dd>
</dl>
<dl>
<dt><code>PCHID</code></dt>
<dd>The user supplied channel identifier storage is overwritten with a
channel identifier if this routine is successful.</dd>
</dl>
<h4>Returns</h4>
<p>ECA_NORMAL - Normal successful completion</p>
<p>ECA_BADTYPE - Invalid DBR_XXXX type</p>
<p>ECA_STRTOBIG - Unusually large string</p>
<p>ECA_ALLOCMEM - Unable to allocate memory</p>
<h3><a name="ca_clear_channel"></a><code>ca_clear_channel()</code></h3>
<pre><code>#include &lt;cadef.h&gt;
int ca_clear_channel (chid CHID);</code></pre>
<h4>Description</h4>
<p>Shutdown and reclaim resources associated with a channel created by
ca_create_channel().</p>
<p>All remote operation requests such as the above are accumulated (buffered)
and not forwarded to the IOC until one of ca_flush_io, ca_pend_io,
ca_pend_event, or ca_sg_pend are called. This allows several requests to be
efficiently sent over the network in one message.</p>
<p>Clearing a channel does not cause its disconnect handler to be called, but
clearing a channel does shutdown and reclaim any channel state change event
subscriptions (monitors) registered with the channel.</p>
<h4>Arguments</h4>
<dl>
<dt><code>CHID</code></dt>
<dd>Identifies the channel to delete.</dd>
</dl>
<h4>Returns</h4>
<p>ECA_NORMAL - Normal successful completion</p>
<p>ECA_BADCHID - Corrupted CHID</p>
<h3><a name="ca_put"><code>ca_put()</code></a></h3>
<pre><code>#include &lt;cadef.h&gt;
int ca_put ( chtype TYPE,
chid CHID, void *PVALUE );
int ca_array_put ( chtype TYPE,
unsigned long COUNT,
chid CHID, const void *PVALUE);
typedef void ( *pCallBack ) (struct event_handler_args );
int ca_put_callback ( chtype TYPE,
chid CHID, const void *PVALUE,
pCallBack PFUNC, void *USERARG );
int ca_array_put_callback ( chtype TYPE,
unsigned long COUNT,
chid CHID, const void *PVALUE,
pCallBack PFUNC, void *USERARG );</code></pre>
<h4>Description</h4>
<p>Write a scalar or array value to a process variable.</p>
<p>When ca_array_put  or ca_put are invoked the client will receive no response
unless the request can not be fulfilled in the server. If unsuccessful an
exception handler is run on the client side. </p>
<p>When ca_array_put_callback are invoked the user supplied asynchronous call
back is called only after the initiated write operation, and all actions
resulting from the initiating write operation, complete.</p>
<p>If unsuccessful the call back function is invoked indicating failure status.
</p>
<p>If the channel disconnects before a put callback request can be completed,
then the client's call back function is called with failure status, but this
does not guarantee that the server did not receive and process the request
before the disconnect. If a connection is lost and then resumed outstanding ca
put requests are not automatically reissued following reconnect.</p>
<p>All of these functions return ECA_DISCONN if the channel is currently
disconnected.</p>
<p>All put requests are accumulated (buffered) and not forwarded to the IOC
until one of ca_flush_io, ca_pend_io, ca_pend_event, or ca_sg_pend are called.
This allows several requests to be efficiently combined into one message.</p>
<h4>Description (IOC Database Specific)</h4>
<p>A CA put request causes the record to process if the record's SCAN field is
set to passive, and the field being written has it's process passive attribute
set to true. If such a record is already processing when a put request is
initiated the specified field is written immediately, and the record is
scheduled to process again as soon as it finishes processing. Earlier instances
of multiple put requests initiated while the record is being processing may be
discarded, but the last put request initiated is always written and
processed.</p>
<p>A CA put <span style="font-style: italic;">callback</span> request causes
the record to process if the record's SCAN field is set to passive, and the
field being written has it's process passive attribute set to true. For such a
record, the user's put callback function is not called until after the record,
and any records that the record links to, finish processing. If such a record
is already processing when a put <span
style="font-style: italic;">callback</span> request is initiated the put <span
style="font-style: italic;">callback</span> request is postponed until the
record, and any records it links to, finish processing.</p>
<p>If the record's SCAN field is not set to passive, or the field being written
has it's process passive attribute set to false then the CA put or CA put
callback request cause the specified field to be immediately written, but they
do not cause the record to be processed.</p>
<h4>Arguments</h4>
<dl>
<dt><code>TYPE</code></dt>
<dd>The external type of the supplied value to be written. Conversion will
occur if this does not match the native type. Specify one from the set of
DBR_XXXX in db_access.h</dd>
</dl>
<dl>
<dt><code>COUNT</code></dt>
<dd>Element count to be written to the specified channel. This must match
the array pointed to by PVALUE.</dd>
</dl>
<dl>
<dt><code>CHID</code></dt>
<dd>Channel identifier</dd>
</dl>
<dl>
<dt><code>PVALUE</code></dt>
<dd>Pointer to a value or array of values provided by the application to be
written to the channel.</dd>
</dl>
<dl>
<dt><code>PFUNC</code></dt>
<dd>address of <a href="#User">user supplied callback function</a> to be
run when the requested operation completes</dd>
</dl>
<dl>
<dt><code>USERARG</code></dt>
<dd>pointer sized variable retained and then passed back to user supplied
function above</dd>
</dl>
<h4>Returns</h4>
<p>ECA_NORMAL - Normal successful completion</p>
<p>ECA_BADCHID - Corrupted CHID</p>
<p>ECA_BADTYPE - Invalid DBR_XXXX type</p>
<p>ECA_BADCOUNT - Requested count larger than native element count</p>
<p>ECA_STRTOBIG - Unusually large string supplied</p>
<p>ECA_NOWTACCESS - Write access denied</p>
<p>ECA_ALLOCMEM - Unable to allocate memory</p>
<p>ECA_DISCONN - Channel is disconnected</p>
<h4>See Also</h4>
ca_flush_io()
<p>ca_pend_event()</p>
<p>ca_sg_array_put()</p>
<h3><a name="ca_get"></a><code>ca_get()</code></h3>
<pre><code>#include &lt;cadef.h&gt;
int ca_get ( chtype TYPE,
chid CHID, void *PVALUE );
int ca_array_get ( chtype TYPE, unsigned long COUNT,
chid CHID, void *PVALUE );
typedef void ( *pCallBack ) (struct event_handler_args );
int ca_get_callback ( chtype TYPE,
chid CHID, pCallBack USERFUNC, void *USERARG);
int ca_array_get_callback ( chtype TYPE, unsigned long COUNT,
chid CHID,
pCallBack USERFUNC, void *USERARG );</code></pre>
<h4>Description</h4>
<p>Read a scalar or array value from a process variable.</p>
<p>When ca_get or ca_array_get are invoked the returned channel value cant be
assumed to be stable in the application supplied buffer until after ECA_NORMAL
is returned from ca_pend_io. If a connection is lost outstanding ca get
requests are not automatically reissued following reconnect.</p>
When ca_get_callback or ca_array_get_callback are invoked a value is read
from the channel and then the user's callback is invoked with a pointer to the
retrieved value. Note that ca_pend_io will not block for the delivery of values
requested by ca_get_callback. If the channel disconnects before a ca get
callback request can be completed, then the clients call back function is
called with failure status.
<p>All of these functions return ECA_DISCONN if the channel is currently
disconnected.</p>
<p>All get requests are accumulated (buffered) and not forwarded to the IOC
until one of ca_flush_io, ca_pend_io, ca_pend_event, or ca_sg_pend are called.
This allows several requests to be efficiently sent over the network in one
message.</p>
<h4>Description (IOC Database Specific)</h4>
<p>A CA get or CA get callback request causes the record's field to be read
immediately independent of whether the record is currently being processed or
not. There is currently no mechanism in place to cause a record to be processed
when a CA get request is initiated.</p>
<h4>Example</h4>
<p>See caExample.c in the example application created by makeBaseApp.pl.</p>
<h4>Arguments</h4>
<dl>
<dt><code>TYPE</code></dt>
<dd>The external type of the user variable to return the value into.
Conversion will occur if this does not match the native type. Specify one
from the set of DBR_XXXX in db_access.h</dd>
</dl>
<dl>
<dt><code>COUNT</code></dt>
<dd>Element count to be read from the specified channel. Must match the
array pointed to by PVALUE.</dd>
</dl>
<dl>
<dt><code>CHID</code></dt>
<dd>Channel identifier</dd>
</dl>
<dl>
<dt><code>PVALUE</code></dt>
<dd>Pointer to an application supplied buffer where the current value of
the channel is to be written.</dd>
</dl>
<dl>
<dt><code>USERFUNC</code></dt>
<dd>Address of <a href="#User">user supplied callback function</a> to be
run when the requested operation completes.</dd>
</dl>
<dl>
<dt><code>USERARG</code></dt>
<dd>Pointer sized variable retained and then passed back to user supplied
call back function above.</dd>
</dl>
<h4>Returns</h4>
<p>ECA_NORMAL - Normal successful completion</p>
<p>ECA_BADTYPE - Invalid DBR_XXXX type</p>
<p>ECA_BADCHID - Corrupted CHID</p>
<p>ECA_BADCOUNT - Requested count larger than native element count</p>
<p>ECA_GETFAIL - A local database get failed</p>
<p>ECA_NORDACCESS - Read access denied</p>
<p>ECA_ALLOCMEM - Unable to allocate memory</p>
<p>ECA_DISCONN - Channel is disconnected</p>
<h4>See Also</h4>
ca_pend_io()
<p>ca_pend_event()</p>
<p>ca_sg_array_get()</p>
<h3><a name="ca_add_event"></a><code>ca_create_subscription()</code></h3>
<pre><code>#include &lt;cadef.h&gt;
typedef void ( *pCallBack ) (
struct event_handler_args );
int ca_create_subscription ( chtype TYPE,
unsigned long COUNT, chid CHID,
unsigned long MASK, pCallBack USERFUNC, void *USERARG,
evid *PEVID );</code></pre>
<h4>Description</h4>
<p>Register a state change subscription and specify a call back function to be
invoked whenever the process variable undergoes significant state changes. A
significant change can be a change in the process variable's value, alarm
status, or alarm severity. In the process control function block database the
deadband field determines the magnitude of a significant change for for the
process variable's value. Each call to this function consumes resources in the
client library and potentially a CA server until one of ca_clear_channel or
ca_clear_event is called.</p>
<p>Subscriptions may be installed or canceled against both connected and
disconnected channels. The specified USERFUNC is called once immediately after
the subscription is installed with the process variable's current state if the
process variable is connected. Otherwise, the specified USERFUNC is called
immediately after establishing a connection (or reconnection) with the process
variable. The specified USERFUNC is called immediately with the process
variable's current state from within ca_add_event() if the client and the
process variable share the same address space.</p>
<p>If a subscription is installed on a channel in a disconnected state then the
requested count will be set to the native maximum element count of the channel
if the requested count is larger.</p>
<p>All subscription requests such as the above are accumulated (buffered) and
not forwarded to the IOC until one of ca_flush_io, ca_pend_io, ca_pend_event,
or ca_sg_pend are called. This allows several requests to be efficiently sent
over the network in one message.</p>
<p>If at any time after subscribing, read access to the specified process
variable is lost, then the call back will be invoked immediately indicating
that read access was lost via the status argument. When read access is restored
normal event processing will resume starting always with at least one update
indicating the current state of the channel.</p>
<p>A better name for this function might have been ca_subscribe.</p>
<h4>Example</h4>
<p>See caMonitor.c in the example application created by makeBaseApp.pl.</p>
<h4>Arguments</h4>
<dl>
<dt><code>TYPE</code></dt>
<dd>The type of value presented to the call back funstion. Conversion will
occur if it does not match native type. Specify one from the set of
DBR_XXXX in db_access.h</dd>
</dl>
<dl>
<dt><code>COUNT</code></dt>
<dd>The element count to be read from the specified channel. A count of
zero specifies the native elemnt count.</dd>
</dl>
<dl>
<dt><code>CHID</code></dt>
<dd>channel identifier</dd>
</dl>
<dl>
<dt><code>USRERFUNC</code></dt>
<dd>The address of <a href="#User">user supplied callback function</a> to
be invoked with each subscription update.</dd>
</dl>
<dl>
<dt><code>USERARG</code></dt>
<dd>pointer sized variable retained and passed back to user callback
function</dd>
</dl>
<dl>
<dt><code>RESERVED</code></dt>
<dd>Reserved for future use. Specify 0.0 to remain upwardly compatible.</dd>
</dl>
<dl>
<dt><code>PEVID</code></dt>
<dd>This is a pointer to user supplied event id which is overwritten if
successful. This event id can later be used to clear a specific
event. This option may may be omitted by passing a nil pointer.</dd>
</dl>
<dl>
<dt><code>MASK</code></dt>
<dd>A mask with bits set for each of the event trigger types requested. The
event trigger mask must be a <em>bitwise or</em> of one or more of the
following constants.
<ul>
<li>DBE_VALUE - Trigger events when the channel value exceeds the
monitor dead band</li>
<li>DBE_ARCHIVE (or DBE_LOG) - Trigger events when the channel value
exceeds the archival dead band</li>
<li>DBE_ALARM - Trigger events when the channel alarm state changes</li>
<li>DBE_PROPERTY - Trigger events when a channel property changes.</li>
</ul>
<p>For functions above that do not include a trigger specification,
events will be triggered when there are significant changes in the
channel's value or when there are changes in the channel's alarm state.
This is the same as "DBE_VALUE | DBE_ALARM."</p>
</dd>
</dl>
<h4>Returns</h4>
<p>ECA_NORMAL - Normal successful completion</p>
<p>ECA_BADCHID - Corrupted CHID</p>
<p>ECA_BADTYPE - Invalid DBR_XXXX type</p>
<p>ECA_ALLOCMEM - Unable to allocate memory</p>
<p>ECA_ADDFAIL - A local database event add failed</p>
<h4>See Also</h4>
ca_pend_event()
<p>ca_flush_io()</p>
<h3><a name="ca_clear_event"></a><code>ca_clear_subscription()</code></h3>
<pre><code>#include &lt;cadef.h&gt;
int ca_clear_subscription ( evid EVID );</code></pre>
<h4>Description</h4>
<p>Cancel a subscription.</p>
<p>All ca_clear_event() requests such as the above are accumulated (buffered)
and not forwarded to the server until one of ca_flush_io, ca_pend_io,
ca_pend_event, or ca_sg_pend are called. This allows several requests to be
efficiently sent together in one message.</p>
<h4>Arguments</h4>
<dl>
<dt>EVID</dt>
<dd>event id returned by ca_add_event()</dd>
</dl>
<h4>Returns</h4>
<p>ECA_NORMAL - Normal successful completion</p>
<p>ECA_BADCHID - Corrupted CHID SEE ALSO ca_add_event()</p>
<h3><a name="ca_pend_io"><code>ca_pend_io()</code></a></h3>
<pre><code>#include &lt;cadef.h&gt;
int ca_pend_io ( double TIMEOUT );</code></pre>
<h4>Description</h4>
<p>This function flushes the send buffer and then blocks until outstanding <a
href="#ca_get">ca_get</a> requests complete, and until channels created
specifying nill connection handler function pointers connect for the first
time.</p>
<ul>
<li>If ECA_NORMAL is returned then it can be safely assumed that all
outstanding <a href="#ca_get">ca_get</a> requests have completed
successfully and channels created specifying nill connection handler
function pointers have connected for the first time.</li>
<li>If ECA_TIMEOUT is returned then it must be assumed for all previous <a
href="#ca_get">ca_get</a> requests and properly qualified first time
channel connects have failed.</li>
</ul>
<p>If ECA_TIMEOUT is returned then get requests may be reissued followed by a
subsequent call to ca_pend_io(). Specifically, the function will block only for
outstanding <a href="#ca_get">ca_get</a> requests issued, and also any channels
created specifying a nill connection handler function pointer, after the last
call to ca_pend_io() or ca client context creation whichever is later. Note
that <a href="#ca_create_channel">ca_create_channel</a> requests generally
should not be reissued for the same process variable unless <a
href="#ca_clear_channel">ca_clear_channel</a> is called first.</p>
<p>If no <a href="#ca_get">ca_get</a> or connection state change events are
outstanding then ca_pend_io() will flush the send buffer and return immediately
<em>without processing any outstanding channel access background
activities</em>.</p>
<p>The delay specified to ca_pend_io() should take into account worst case
network delays such as Ethernet collision exponential back off until
retransmission delays which can be quite long on overloaded networks.</p>
<p>Unlike <code><a href="#L3249">ca_pend_event</a></code>, this routine will
not process CA's background activities if none of the selected IO requests are
pending.</p>
<h4>Arguments</h4>
<dl>
<dt>TIMEOUT</dt>
<dd>Specifies the time out interval. A <code>TIMEOUT</code> interval of
zero specifies forever.</dd>
</dl>
<h4>Returns</h4>
<p>ECA_NORMAL - Normal successful completion</p>
<p>ECA_TIMEOUT - Selected IO requests didnt complete before specified
timeout</p>
<p>ECA_EVDISALLOW - Function inappropriate for use within an event handler</p>
<h4>See Also</h4>
<a href="#ca_get">ca_get</a>()
<p><a href="#ca_create_channel">ca_create_channel</a>()</p>
<p><a href="#ca_test_io">ca_test_io</a>()</p>
<h3><a name="ca_test_io"><code>ca_test_io()</code></a></h3>
<pre><code>#include &lt;cadef.h&gt;
int ca_test_io();</code></pre>
<h4>Description</h4>
<p>This function tests to see if all <a href="#ca_get">ca_get</a> requests are
complete and channels created specifying a nill connection callback function
pointer are connected. It will report the status of outstanding <a
href="#ca_get">ca_get</a> requests issued, and channels created specifying a
nill connection callback function pointer, after the last call to ca_pend_io()
or CA context initialization whichever is later.</p>
<h4>Returns</h4>
<p>ECA_IODONE - All IO operations completed</p>
<p>ECA_IOINPROGRESS - IO operations still in progress</p>
<h4>See Also</h4>
<p><a href="#ca_pend_io">ca_pend_io</a>()</p>
<h3><code><a name="L3249">ca_pend_event()</a></code></h3>
<pre>#include &lt;cadef.h&gt;
int ca_pend_event ( double TIMEOUT );
int ca_poll ();</pre>
<h4>Description</h4>
<p>When ca_pend_event is invoked the send buffer is flushed and CA background
activity is processed for TIMEOUT seconds.</p>
<p>When ca_poll is invoked the send buffer is flushed and any outstanding CA
background activity is processed.</p>
<p>The ca_pend_event function will <em>not</em> return before the specified
time-out expires and all unfinished channel access labor has been processed,
and unlike <code><a href="#ca_pend_io">ca_pend_io</a></code> returning from the
function does <em>not </em>indicate anything about the status of pending IO
requests.</p>
<p>Both <code>ca_pend_event</code> and <code>ca_poll</code> return ECA_TIMEOUT
when successful. This behavior probably isn't intuitive, but it is preserved to
insure backwards compatibility.</p>
<p>See also <a href="#Thread">Thread Safety and Preemptive Callback to User
Code</a>.</p>
<h4>Arguments</h4>
<dl>
<dt><code>TIMEOUT</code></dt>
<dd>The duration to block in this routine in seconds. A timeout of zero
seconds blocks forever.</dd>
</dl>
<h4>Returns</h4>
<p>ECA_TIMEOUT - The operation timed out</p>
<p>ECA_EVDISALLOW - Function inappropriate for use within a call back
handler</p>
<h3><code><a name="ca_flush_io">ca_flush_io()</a></code></h3>
<pre>#include &lt;cadef.h&gt;
int ca_flush_io();</pre>
<h4>Description</h4>
<p>Flush outstanding IO requests to the server. This routine might be useful
to users who need to flush requests prior to performing client side labor in
parallel with labor performed in the server.</p>
<p>Outstanding requests are also sent whenever the buffer which holds them
becomes full.</p>
<h4>Returns</h4>
<p>ECA_NORMAL - Normal successful completion</p>
<h3><code><a name="ca_signal">ca_signal</a>()</code></h3>
<pre><code>#include &lt;cadef.h&gt;
int ca_signal ( long CA_STATUS, const char * CONTEXT_STRING );
void SEVCHK( CA_STATUS, CONTEXT_STRING );</code></pre>
<h4>Description</h4>
<p>Provide the error message character string associated with the supplied
channel access error code and the supplied error context to diagnostics. If the
error code indicates an unsuccessful operation a stack dump is printed, if this
capability is available on the local operating system, and execution is
terminated.</p>
<p>SEVCHK is a macro envelope around ca_signal which only calls ca_signal() if
the supplied error code indicates an unsuccessful operation. SEVCHK is the
recommended error handler for simple applications which do not wish to write
code testing the status returned from each channel access call.</p>
<h4>Examples</h4>
<pre><code>status = ca_context_create (...);
SEVCHK ( status, "Unable to create a CA client context" );</code></pre>
<p>If the application only wishes to print the message associated with an error
code or test the severity of an error there are also functions provided for
this purpose.</p>
<h4>Arguments</h4>
<dl>
<dt><code>CA_STATUS</code></dt>
<dd>The status (error code) returned from a channel access function.</dd>
</dl>
<dl>
<dt><code>CONTEXT_STRING</code></dt>
<dd>A null terminated character string to supply as error context to
diagnostics.</dd>
</dl>
<h4>Returns</h4>
<p>ECA_NORMAL - Normal successful completion</p>
<h3><code><a
name="ca_add_exception_event">ca_add_exception_event()</a></code></h3>
<pre>#include &lt;cadef.h&gt;
typedef void (*pCallback) ( struct exception_handler_args HANDLERARGS );
int ca_add_exception_event ( pCallback USERFUNC, void *USERARG );</pre>
<h4>Description</h4>
<p>Replace the currently installed CA context global exception handler call
back.</p>
<p>When an error occurs in the server asynchronous to the clients thread then
information about this type of error is passed from the server to the client in
an exception message. When the client receives this exception message an
exception handler callback is called.The default exception handler prints a
diagnostic message on the client's standard out and terminates execution if the
error condition is severe.</p>
<p>Note that certain fields in "struct exception_handler_args" are not
applicable in the context of some error messages. For instance, a failed get
will supply the address in the client task where the returned value was
requested to be written. For other failed operations the value of the addr
field should not be used.</p>
<h4>Arguments</h4>
<dl>
<dt><code>USERFUNC</code></dt>
<dd>Address of user callback function to be executed when an exceptions
occur. Passing a nil value causes the default exception handler to be
reinstalled. The following structure is passed by value to the user's
callback function. Currently, the <code>op </code>field can be one of
<code>CA_OP_GET, CA_OP_PUT, CA_OP_CREATE_CHANNEL, CA_OP_ADD_EVENT,
CA_OP_CLEAR_EVENT, or CA_OP_OTHER.</code>
<pre><code>struct exception_handler_args {
void *usr; /* user argument supplied when installed */
chanId chid; /* channel id (may be nill) */
long type; /* type requested */
long count; /* count requested */
void *addr; /* user's address to write results of CA_OP_GET */
long stat; /* channel access ECA_XXXX status code */
long op; /* CA_OP_GET, CA_OP_PUT, ..., CA_OP_OTHER */
const char *ctx; /* a character string containing context info */
sonst char *pFile; /* source file name (may be NULL) */
unsigned lineNo; /* source file line number (may be zero) */
};</code></pre>
</dd>
</dl>
<dl>
<dt><code>USERARG</code></dt>
<dd>pointer sized variable retained and passed back to user function
above</dd>
</dl>
<h4>Example</h4>
<pre><code>void ca_exception_handler (
struct exception_handler_args args)
{
char buf[512];
char *pName;
if ( args.chid ) {
pName = ca_name ( args.chid );
}
else{
pName = "?";
}
sprintf ( buf,
"%s - with request chan=%s op=%d data type=%s count=%d",
args.ctx, pName, args.op, dbr_type_to_text ( args.type ), args.count );
ca_signal ( args.stat, buf );
}
ca_add_exception_event ( ca_exception_handler , 0 );</code></pre>
<h4>Returns</h4>
<p>ECA_NORMAL - Normal successful completion</p>
<p></p>
<h3><code><a name="ca_add_fd_"
id="ca_add_fd_">ca_add_fd_registration()</a></code></h3>
<pre><code>#include &lt;cadef.h&gt;</code><code>int ca_add_fd_registration ( </code><code>void ( USERFUNC * ) ( void *USERARG, int FD, int OPENED ), </code><code>void * USERARG </code><code>)</code></pre>
<h4>Description</h4>
<p>For use with the services provided by a file descriptor manager (IO
multiplexor) such as ""fdmgr.c". A file descriptor manager is often needed when
two file descriptor IO intensive libraries such as the EPICS channel access
client library and the X window system client library must coexist in the same
UNIX process. This function allows an application code to be notified whenever
the CA client library places a new file descriptor into service and whenever
the CA client library removes a file descriptor from service. Specifying
USERFUNC=NULL disables file descriptor registration (this is the default).</p>
<h4>Arguments</h4>
<p>USERFUNC</p>
<p>Pointer to a user supplied C function returning null with the above
arguments.</p>
<p>USERARG</p>
<p>User supplied pointer sized variable passed to the above function.</p>
<p>FD </p>
<p>A file descriptor.</p>
<p>OPENED </p>
<p>Boolean argument is true if the file descriptor was opened and false if the
file descriptor was closed.</p>
<h4>Example</h4>
<pre><code>int s;</code></pre>
<pre><code>static struct myStruct aStruct;</code></pre>
<pre></pre>
<pre><code>void fdReg ( </code><code>struct myStruct *pStruct,</code><code> int fd,</code><code> int opened )</code></pre>
<pre><code>{</code></pre>
<pre><code> if ( opened ) printf ( "fd %d was opened\n", fd );</code></pre>
<pre><code> else printf ( "fd %d was closed\n", fd );</code></pre>
<pre><code>}</code></pre>
<pre><code>s = ca_add_fd_registration ( fdReg, &amp; aStruct );</code></pre>
<pre><code>SEVCHK ( s, NULL );</code></pre>
<p><code></code></p>
<h4>Comments</h4>
<p>When using this function it is advisable to call it only once prior to
calling any other CA function, or once just after creating the CA context (if
you create the context explicitly). Use of this interface can improve latency
slightly in applications that use non preemptive callback mode at the expense
of some additional runtime overhead when compared to the alternative which is
just polling ca_pend_event periodically. It would probably not be appropriate
to use this function with preemptive callback mode. Starting with R3.14 this
function is implemented in a special backward compatibility mode. if
<code>ca_add_fd_registration</code> is called, a single pseudo UDP fd is
created which CA pokes whenever something significant happens. Xt and others
can watch this fd so that backwards compatibility is preserved, and so that
they will not need to use preemptive callback mode but they will nevertheless
get the lowest latency response to the arrival of CA messages.</p>
<h4>Returns</h4>
<p>"ECA_NORMAL - Normal successful completion</p>
<p></p>
<h3><code><a name="ca_replace_printf_handler">ca_replace_printf_handler
()</a></code></h3>
<pre><code>#include &lt;cadef.h&gt;
typedef int caPrintfFunc ( const char *pFromat, va_list args );
int ca_replace_printf_handler ( caPrintfFunc *PFUNC );</code></pre>
<h4>Description</h4>
<p>Replace the default handler for formatted diagnostic message output. The
default handler uses fprintf to send messages to 'stderr'.</p>
<h4>Arguments</h4>
<dl>
<dt><code>PFUNC</code></dt>
<dd>The address of a user supplied call back handler to be invoked when CA
prints diagnostic messages. Installing a nil pointer will cause the
default call back handler to be reinstalled.</dd>
</dl>
<h4>Examples</h4>
<pre><code>int my_printf ( char *pformat, va_list args ) {
int status;
status = vfprintf( stderr, pformat, args);
return status;
}
status = ca_replace_printf_handler ( my_printf );
SEVCHK ( status, "failed to install my printf handler" );</code></pre>
<h4>Returns</h4>
<p>ECA_NORMAL - Normal successful completion</p>
<h3><code><a name="ca_replace">ca_replace_access_rights_event()</a></code></h3>
<pre><code>#include &lt;cadef.h&gt;
typedef void ( *pCallBack )( struct access_rights_handler_args );
int ca_replace_access_rights_event ( chid CHAN, pCallBack PFUNC );</code></pre>
<h4>Description</h4>
<p>Install or replace the access rights state change callback handler for the
specified channel.</p>
<p>The callback handler is called in the following situations.</p>
<ul>
<li>whenever CA connects the channel immediately before the channel's
connection handler is called</li>
<li>whenever CA disconnects the channel immediately after the channel's
disconnect call back is called</li>
<li>once immediately after installation if the channel is connected.</li>
<li>whenever the access rights state of a connected channel changes</li>
</ul>
<p>When a channel is created no access rights handler is installed.</p>
<h4>Arguments</h4>
<dl>
<dt><code>CHAN</code></dt>
<dd>The channel identifier.</dd>
</dl>
<dl>
<dt><code>PFUNC</code></dt>
<dd>Address of user supplied call back function. A nil pointer uninstalls
the current handler. The following arguments are passed <em>by value</em>
to the supplied callback handler.
<pre><code>typedef struct ca_access_rights {
unsigned read_access:1;
unsigned write_access:1;
} caar;
/* arguments passed to user access rights handlers */
struct access_rights_handler_args {
chanId chid; /* channel id */
caar ar; /* new access rights state */
};</code></pre>
</dd>
</dl>
<h4>Returns</h4>
<p>ECA_NORMAL - Normal successful completion</p>
<h4>See Also</h4>
<p>ca_modify_user_name()</p>
<p>ca_modify_host_name()</p>
<h3><code><a name="L6925">ca_field_type()</a></code></h3>
<pre><code>#include &lt;cadef.h&gt;
chtype ca_field_type ( CHID );</code></pre>
<h4>Description</h4>
<p>Return the native type in the server of the process variable.</p>
<h4>Arguments</h4>
<dl>
<dt><code>CHID</code></dt>
<dd>channel identifier</dd>
</dl>
<h4>Returns</h4>
<dl>
<dt><code>TYPE</code></dt>
<dd>The data type code will be a member of the set of DBF_XXXX in
db_access.h. The constant TYPENOTCONN is returned if the channel is
disconnected.<a name="ca_element_count"></a></dd>
</dl>
<h3><code>ca_element_count()</code></h3>
<pre><code>#include &lt;cadef.h&gt;
unsigned ca_element_count ( CHID );</code></pre>
<h4>Description</h4>
<p>Return the maximum array element count in  the server for the specified IO
channel.</p>
<h4>Arguments</h4>
<dl>
<dt><code>CHID</code></dt>
<dd>channel identifier</dd>
</dl>
<h4>Returns</h4>
<dl>
<dt><code>COUNT</code></dt>
<dd>The maximum array element count in  the server. An element count of
zero is returned if the channel is disconnected.</dd>
</dl>
<h3><code><a name="L6931">ca_name()</a></code></h3>
<pre><code>#include &lt;cadef.h&gt;
char * ca_name ( CHID );</code></pre>
<h4>Description</h4>
<p>Return the name provided when the supplied channel id was created.</p>
<h4>Arguments</h4>
<dl>
<dt><code>CHID</code></dt>
<dd>channel identifier</dd>
</dl>
<h4>Returns</h4>
<dl>
<dt><code>PNAME</code></dt>
<dd>The channel name. The string returned is valid as long as the channel
specified exists.</dd>
</dl>
<h3><code><a name="ca_set_puser">ca_set_puser()</a></code></h3>
<pre><code>#include &lt;cadef.h&gt;
void ca_set_puser ( chid CHID, void *PUSER );</code></pre>
<h4>Description</h4>
<p>Set a user private void pointer variable retained with each channel for use
at the users discretion.</p>
<h4>Arguments</h4>
<dl>
<dt>CHID</dt>
<dd>channel identifier</dd>
</dl>
<dl>
<dt>PUSER</dt>
<dd>user private void pointer</dd>
</dl>
<h3><code><a name="ca_puser">ca_puser()</a></code></h3>
<pre><code>#include &lt;cadef.h&gt;
void * ca_puser ( CHID );</code></pre>
<h4>Description</h4>
<p>Return a user private void pointer variable retained with each channel for
use at the users discretion.</p>
<h4>Arguments</h4>
<dl>
<dt><code>CHID</code></dt>
<dd>channel identifier</dd>
</dl>
<h4>Returns</h4>
<dl>
<dt><code>PUSER</code></dt>
<dd>user private pointer</dd>
</dl>
<h3><code><a name="ca_state">ca_state()</a></code></h3>
<pre><code>#include &lt;cadef.h&gt;
enum channel_state {
cs_never_conn, /* valid chid, server not found or unavailable */
cs_prev_conn, /* valid chid, previously connected to server */
cs_conn, /* valid chid, connected to server */
cs_closed }; /* channel deleted by user */
enum channel_state ca_state ( CHID );</code></pre>
<h4>Description</h4>
<p>Returns an enumerated type indicating the current state of the specified IO
channel.</p>
<h4>Arguments</h4>
<dl>
<dt><code>CHID</code></dt>
<dd>channel identifier</dd>
</dl>
<h4>Returns</h4>
<dl>
<dt><code>STATE</code></dt>
<dd>the connection state</dd>
</dl>
<h3><code><a name="L6929">ca_message()</a></code></h3>
<pre><code>#include &lt;cadef.h&gt;
const char * ca_message ( STATUS );</code></pre>
<h4>Description</h4>
<p>return a message character string corresponding to a user specified CA
status code.</p>
<h4>Arguments</h4>
<dl>
<dt><code>STATUS</code></dt>
<dd>a CA status code</dd>
</dl>
<h4>Returns</h4>
<dl>
<dt>STR<code></code>ING</dt>
<dd>the corresponding error message string</dd>
</dl>
<h3><code><a name="L6927">ca_host_name()</a></code></h3>
<pre><code>#include &lt;cadef.h&gt;
char * ca_host_name ( CHID );</code></pre>
<h4>Description</h4>
<p>Return a character string which contains the name of the host to which a
channel is currently connected.</p>
<h4>Arguments</h4>
<dl>
<dt><code>CHID</code></dt>
<dd>the channel identifier</dd>
</dl>
<h4>Returns</h4>
<dl>
<dt><code>STRING</code></dt>
<dd>The process variable server's host name. If the channel is disconnected
the string "&lt;disconnected&gt;" is returned.</dd>
</dl>
<h3><code><a name="L6933">ca_read_access()</a></code></h3>
<pre><code>#include &lt;cadef.h&gt;
int ca_read_access ( CHID );</code></pre>
<h4>Description</h4>
<p>Returns boolean true if the client currently has read access to the
specified channel and boolean false otherwise.</p>
<h4>Arguments</h4>
<dl>
<dt><code>CHID</code></dt>
<dd>the channel identifier</dd>
</dl>
<h4>Returns</h4>
<dl>
<dt><code>STRING</code></dt>
<dd>boolean true if the client currently has read access to the specified
channel and boolean false otherwise</dd>
</dl>
<h3><code><a name="L6941">ca_write_access()</a></code></h3>
<pre><code>#include &lt;cadef.h&gt;
int ca_write_access ( CHID );</code></pre>
<h4>Description</h4>
<p>Returns boolean true if the client currently has write access to the
specified channel and boolean false otherwise.</p>
<h4>Arguments</h4>
<dl>
<dt><code>CHID</code></dt>
<dd>the channel identifier</dd>
</dl>
<h4>Returns</h4>
<dl>
<dt><code>STRING</code></dt>
<dd>boolean true if the client currently has write access to the specified
channel and boolean false otherwise</dd>
</dl>
<h3><code><a name="dbr_size[]">dbr_size[]</a></code></h3>
<pre><code>#include &lt;db_access.h&gt;
extern unsigned dbr_size[/*TYPE*/];</code></pre>
<h4>Description</h4>
<p>An array that returns the size in bytes for a DBR_XXXX type.</p>
<h4>Arguments</h4>
<dl>
<dt><code>TYPE</code></dt>
<dd>The data type code. A member of the set of DBF_XXXX in db_access.h.</dd>
</dl>
<h4>Returns</h4>
<dl>
<dt><code>SIZE</code></dt>
<dd>the size in bytes of the specified type</dd>
</dl>
<h3><code><a name="L6946">dbr_size_n()</a></code></h3>
<pre><code>#include &lt;db_access.h&gt;
unsigned dbr_size_n ( TYPE, COUNT );</code></pre>
<h4>Description</h4>
<p>Returns the size in bytes for a DBR_XXXX type with COUNT elements. If the
DBR type is a structure then the value field is the last field in the
structure. If COUNT is greater than one then COUNT-1 elements are appended to
the end of the structure so that they can be addressed as an array through a
pointer to the value field.</p>
<h4>Arguments</h4>
<dl>
<dt><code>TYPE</code></dt>
<dd>The data type</dd>
</dl>
<dl>
<dt><code>COUNT</code></dt>
<dd>The element count</dd>
</dl>
<h4>Returns</h4>
<dl>
<dt><code>SIZE</code></dt>
<dd>the size in bytes of the specified type with the specified number of
elements</dd>
</dl>
<h3><code><a name="dbr_value_size">dbr_value_size[]</a></code></h3>
<pre><code>#include &lt;db_access.h&gt;
extern unsigned dbr_value_size[/* TYPE */];</code></pre>
<h4>Description</h4>
<p>The array dbr_value_size[TYPE] returns the size in bytes for the value
stored in a DBR_XXXX type. If the type is a structure the size of the value
field is returned otherwise the size of the type is returned.</p>
<h4>Arguments</h4>
<dl>
<dt><code>TYPE</code></dt>
<dd>The data type code. A member of the set of DBF_XXXX in db_access.h.</dd>
</dl>
<h4>Returns</h4>
<dl>
<dt><code>SIZE</code></dt>
<dd>the size in bytes of the value field if the type is a structure and
otherwise the size in bytes of the type</dd>
</dl>
<h3><code><a name="dbr_type_t">dbr_type_to_text</a>()</code></h3>
<pre><code>#include &lt;db_access.h&gt;
const char * dbr_type_text ( chtype TYPE );</code></pre>
<h4>Description</h4>
<p>Returns a constant null terminated string corresponding to the specified dbr
type.</p>
<h4>Arguments</h4>
<dl>
<dt><code>TYPE</code></dt>
<dd>The data type code. A member of the set of DBR_XXXX in db_access.h.</dd>
</dl>
<h4>Returns</h4>
<dl>
<dt><code>STRING</code></dt>
<dt></dt>
<dd>The const string corresponding to the DBR_XXX type.</dd>
</dl>
<h3><code><a name="ca_test_event">ca_test_event()</a></code></h3>
<pre>#include &lt;cadef.h&gt;</pre>
<h4>Description</h4>
<pre>void ca_test_event ( struct event_handler_args );</pre>
<p>A built-in subscription update call back handler for debugging purposes that
prints diagnostics to standard out.</p>
<h4>Examples</h4>
<pre><code>void ca_test_event ();
status = ca_add_event ( type, chid, ca_test_event, NULL, NULL );
SEVCHK ( status, .... );</code></pre>
<h4>See Also</h4>
<p><a href="#ca_add_event">ca_add_event</a>()</p>
<h3><code><a name="ca_sg_create">ca_sg_create()</a></code></h3>
<pre><code>#include &lt;cadef.h&gt;
int ca_sg_create ( CA_SYNC_GID *PGID );</code></pre>
<h4>Description</h4>
<p>Create a synchronous group and return an identifier for it.</p>
<p>A synchronous group can be used to guarantee that a set of channel access
requests have completed. Once a synchronous group has been created then channel
access get and put requests may be issued within it using ca_sg_get() and
ca_sg_put() respectively. The routines ca_sg_block() and ca_sg_test() can be
used to block for and test for completion respectively. The routine
ca_sg_reset() is used to discard knowledge of old requests which have timed out
and in all likelihood will never be satisfied.</p>
<p>Any number of asynchronous groups can have application requested operations
outstanding within them at any given time.</p>
<h4>Arguments</h4>
<dl>
<dt><code>PGID</code></dt>
<dd>Pointer to a user supplied CA_SYNC_GID.</dd>
</dl>
<h4>Examples</h4>
<pre><code>CA_SYNC_GID gid;
status = ca_sg_create ( &amp;gid );
SEVCHK ( status, Sync group create failed );</code></pre>
<h4>Returns</h4>
<p>ECA_NORMAL - Normal successful completion</p>
<p>ECA_ALLOCMEM - Failed, unable to allocate memory</p>
<h4>See Also</h4>
ca_sg_delete()
<p>ca_sg_block()</p>
<p>ca_sg_test()</p>
<p>ca_sg_reset()</p>
<p>ca_sg_put()</p>
<p>ca_sg_get()</p>
<h3><code><a name="ca_sg_delete">ca_sg_delete()</a></code></h3>
<pre><code>#include &lt;cadef.h&gt;
int ca_sg_delete ( CA_SYNC_GID GID );</code></pre>
<h4>Description</h4>
<p>Deletes a synchronous group.</p>
<h4>Arguments</h4>
<dl>
<dt>GID</dt>
<dd>Identifier of the synchronous group to be deleted.</dd>
</dl>
<h4>Examples</h4>
<pre><code>CA_SYNC_GID gid;
status = ca_sg_delete ( gid );
SEVCHK ( status, Sync group delete failed );</code></pre>
<h4>Returns</h4>
<p>ECA_NORMAL - Normal successful completion</p>
<p>ECA_BADSYNCGRP - Invalid synchronous group</p>
<h4>See Also</h4>
<p><a href="#ca_sg_create">ca_sg_create</a>()</p>
<h3><a name="ca_sg_block"><code>ca_sg_block</code></a><code>()</code></h3>
<pre><code>#include &lt;cadef.h&gt;
int ca_sg_block ( CA_SYNC_GID GID, double timeout );</code></pre>
<h4>Description</h4>
<p>Flushes the send buffer and then waits until outstanding requests complete
or the specified time out expires. At this time outstanding requests include
calls to ca_sg_array_get() and calls to ca_sg_array_put(). If ECA_TIMEOUT is
returned then failure must be assumed for all outstanding queries. Operations
can be reissued followed by another ca_sg_block(). This routine will only block
on outstanding queries issued after the last call to ca_sg_block(),
ca_sg_reset(), or ca_sg_create() whichever occurs later in time. If no queries
are outstanding then ca_sg_block() will return immediately without processing
any pending channel access activities.</p>
<p>Values written into your program's variables by a channel access synchronous
group request should not be referenced by your program until ECA_NORMAL has
been received from ca_sg_block(). This routine will process pending channel
access background activity while it is waiting.</p>
<h4>Arguments</h4>
<dl>
<dt>GID</dt>
<dd>Identifier of the synchronous group.</dd>
</dl>
<h4>Examples</h4>
<pre><code>CA_SYNC_GID gid;
status = ca_sg_block(gid);
SEVCHK(status, Sync group block failed);</code></pre>
<h4>Returns</h4>
<p>ECA_NORMAL - Normal successful completion</p>
<p>ECA_TIMEOUT - The operation timed out</p>
<p>ECA_EVDISALLOW - Function inappropriate for use within an event handler</p>
<p>ECA_BADSYNCGRP - Invalid synchronous group</p>
<h4>See Also</h4>
<p>ca_sg_test()</p>
<p>ca_sg_reset()</p>
<h3><code><a name="ca_sg_test">ca_sg_test()</a></code></h3>
<pre><code>#include &lt;cadef.h&gt;
int ca_sg_test  ( CA_SYNC_GID GID )</code></pre>
<h4>Description</h4>
<p>Test to see if all requests made within a synchronous group have
completed.</p>
<h4>Arguments</h4>
<dl>
<dt><code>GID</code></dt>
<dd>Identifier of the synchronous group.</dd>
</dl>
<h4>Description</h4>
<p>Test to see if all requests made within a synchronous group have
completed.</p>
<h4>Examples</h4>
<pre><code>CA_SYNC_GID gid;
status = ca_sg_test ( gid );</code></pre>
<h4>Returns</h4>
<p>ECA_IODONE - IO operations completed</p>
<p>ECA_IOINPROGRESS - Some IO operations still in progress</p>
<h3><code><a name="ca_sg_reset">ca_sg_reset()</a></code></h3>
<pre><code>#include &lt;cadef.h&gt;
int ca_sg_reset ( CA_SYNC_GID GID )</code></pre>
<h4>Description</h4>
<p>Reset the number of outstanding requests within the specified synchronous
group to zero so that ca_sg_test() will return ECA_IODONE and ca_sg_block()
will not block unless additional subsequent requests are made.</p>
<h4>Arguments</h4>
<dl>
<dt><code>GID</code></dt>
<dd>Identifier of the synchronous group.</dd>
</dl>
<h4>Examples</h4>
<pre><code>CA_SYNC_GID gid;
status = ca_sg_reset(gid);</code></pre>
<h4>Returns</h4>
<p>ECA_NORMAL - Normal successful completion</p>
<p>ECA_BADSYNCGRP - Invalid synchronous group</p>
<h3><code><a name="ca_sg_put">ca_sg_put()</a></code></h3>
<pre><code>#include &lt;cadef.h&gt;
int ca_sg_array_put ( CA_SYNC_GID GID, chtype TYPE,
unsigned long COUNT, chid CHID, void *PVALUE );</code></pre>
<p>Write a value, or array of values, to a channel and increment the
outstanding request count of a synchronous group. The ca_sg_array_put
functionality is implemented using ca_array_put_callback.</p>
<p>All remote operation requests such as the above are accumulated (buffered)
and not forwarded to the server until one of ca_flush_io(), ca_pend_io(),
ca_pend_event(), or ca_sg_pend() are called. This allows several requests to be
efficiently sent in one message.</p>
<p>If a connection is lost and then resumed outstanding puts are not
reissued.</p>
<h4>Arguments</h4>
<dl>
<dt><code>GID</code></dt>
<dd>synchronous group identifier</dd>
</dl>
<dl>
<dt><code>TYPE</code></dt>
<dd>The type of supplied value. Conversion will occur if it does not match
the native type. Specify one from the set of DBR_XXXX in db_access.h.</dd>
</dl>
<dl>
<dt><code>COUNT</code></dt>
<dd>element count to be written to the specified channel - must match the
array pointed to by PVALUE</dd>
</dl>
<dl>
<dt><code>CHID</code></dt>
<dd>channel identifier</dd>
</dl>
<dl>
<dt><code>PVALUE</code></dt>
<dd>A pointer to an application supplied buffer containing the value or
array of values returned</dd>
</dl>
<h4>Returns</h4>
<p>ECA_NORMAL - Normal successful completion</p>
<p>ECA_BADSYNCGRP - Invalid synchronous group</p>
<p>ECA_BADCHID - Corrupted CHID</p>
<p>ECA_BADTYPE - Invalid DBR_XXXX type</p>
<p>ECA_BADCOUNT - Requested count larger than native element count</p>
<p>ECA_STRTOBIG - Unusually large string supplied</p>
<p>ECA_PUTFAIL - A local database put failed</p>
<h4>See Also</h4>
<p><a href="#ca_flush_io">ca_flush_io</a>()</p>
<h3><code><a name="ca_sg_get">ca_sg_get()</a></code></h3>
<pre><code>#include &lt;cadef.h&gt;
int ca_sg_array_get ( CA_SYNC_GID GID,
chtype TYPE, unsigned long COUNT,
chid CHID, void *PVALUE );</code></pre>
<h4>Description</h4>
<p>Read a value from a channel and increment the outstanding request count of a
synchronous group. The ca_sg_array_get functionality is implemented using
ca_array_get_callback.</p>
<p>The values written into your program's variables by ca_sg_get should not be
referenced by your program until ECA_NORMAL has been received from ca_sg_block
, or until ca_sg_test returns ECA_IODONE.</p>
<p>All remote operation requests such as the above are accumulated (buffered)
and not forwarded to the server until one of ca_flush_io, ca_pend_io,
ca_pend_event, or ca_sg_pend are called. This allows several requests to be
efficiently sent in one message.</p>
<p>If a connection is lost and then resumed outstanding gets are not
reissued.</p>
<h4>Arguments</h4>
<dl>
<dt><code>GID</code></dt>
<dd>Identifier of the synchronous group.</dd>
</dl>
<dl>
<dt><code>TYPE</code></dt>
<dd>External type of returned value. Conversion will occur if this does not
match native type. Specify one from the set of DBR_XXXX in
db_access.h</dd>
</dl>
<dl>
<dt><code>COUNT</code></dt>
<dd>Element count to be read from the specified channel. It must match the
array pointed to by PVALUE.</dd>
</dl>
<dl>
<dt><code>CHID</code></dt>
<dd>channel identifier</dd>
</dl>
<dl>
<dt><code>PVALUE</code></dt>
<dd>Pointer to application supplied buffer that is to contain the value or
array of values to be returned</dd>
</dl>
<h4>Returns</h4>
<p>ECA_NORMAL - Normal successful completion </p>
<p>ECA_BADSYNCGRP - Invalid synchronous group </p>
<p>ECA_BADCHID - Corrupted CHID</p>
<p>ECA_BADCOUNT - Requested count larger than native element count</p>
<p>ECA_BADTYPE - Invalid DBR_XXXX type</p>
<p>ECA_GETFAIL - A local database get failed</p>
<h4>See Also</h4>
<p><a href="#ca_pend_io">ca_pend_io</a>()</p>
<p><a href="#ca_flush_io">ca_flush_io</a>()</p>
<p><a href="#ca_get">ca_get_callback</a>()</p>
<h3><code><a name="ca_client_status">ca_client_status()</a></code></h3>
<pre>int ca_client_status ( unsigned level );
int ca_context_status ( struct ca_client_context *,
unsigned level );</pre>
<h4>Description</h4>
<p>Prints information about the client context including, at higher interest
levels, status for each channel. Lacking a CA context pointer,
ca_client_status() prints information about the calling threads CA context.</p>
<h4>Arguments</h4>
<dl>
<dt><code>CONTEXT</code></dt>
<dd>A pointer to the CA context to join with.</dd>
<dt><code>LEVEL</code></dt>
<dd>The interest level. Increasing level produces increasing detail.</dd>
</dl>
<h3><a name="ca_current_context">ca_current_context()</a></h3>
<pre>struct ca_client_context * ca_current_context ();</pre>
<h4>Description</h4>
<p>Returns a pointer to the current thread's CA context. If none then nil is
returned.</p>
<h4>See Also</h4>
<p>ca_attach_context()</p>
<p>ca_detach_context()</p>
<p>ca_context_create()</p>
<p>ca_context_destroy()</p>
<h3><a name="ca_attach_context">ca_attach_context()</a></h3>
<pre>int ca_attach_context (struct ca_client_context *CONTEXT);</pre>
<h4>Description</h4>
<p>The calling thread becomes a member of the specified CA context. If
<code>ca_disable_preemptive_callback</code> is specified when
ca_context_create() is called (or if ca_task_initialize() is called) then
additional threads are <em>not </em>allowed to join the CA context because
allowing other threads to join implies that CA callbacks will be called
preemptively from more than one thread.</p>
<h4>Arguments</h4>
<dl>
<dt><code>CONTEXT</code></dt>
<dd>A pointer to the CA context to join with.</dd>
</dl>
<h4>Returns</h4>
<p>ECA_ISATTACHED - already attached to a CA context</p>
<p>ECA_NOTTHREADED - the specified context is non-preemptive and therefore does
not allow other threads to join</p>
<p>ECA_ISATTACHED - the current thread is already attached to a CA context</p>
<h4>See Also</h4>
<p>ca_current_context()</p>
<p>ca_detach_context()</p>
<p>ca_context_create()</p>
<p>ca_context_destroy()</p>
<h3><a name="ca_detach_" id="ca_detach_">ca_detach_context()</a></h3>
<pre>void ca_detach_context();</pre>
<h4>Description</h4>
<p>Detach from any CA context currently attached to the calling thread. This
does <em>not</em> cleanup or shutdown any currently attached CA context (for
that use ca_context_destroy).</p>
<h4>See Also</h4>
<p>ca_current_context()</p>
<p>ca_attach_context()</p>
<p>ca_context_create()</p>
<p>ca_context_destroy()</p>
<h3><a name="ca_dump_db">ca_dump_dbr()</a></h3>
<p><code>void ca_dump_dbr ( </code><code>chtype TYPE, unsigned COUNT, const
void * PDBR );</code></p>
<h4>Description</h4>
<p>Dumps the specified dbr data type to standard out.</p>
<h4>Arguments</h4>
<dl>
<dt><code>TYPE</code></dt>
<dd>The data type (from the DBR_XXX set described in db_access.h).</dd>
<dt><code>COUNT</code></dt>
<dd>The array element count</dd>
<dt><code>PDBR</code></dt>
<dd>A pointer to data of the specified count and number.</dd>
</dl>
<h2><a name="Return">Return Codes</a></h2>
<dl>
<dt>ECA_NORMAL</dt>
<dd>Normal successful completion</dd>
<dt>ECA_ALLOCMEM</dt>
<dd>Unable to allocate additional dynamic memory</dd>
<dt>ECA_TOLARGE</dt>
<dd>The requested data transfer is greater than available memory or
EPICS_CA_MAX_ARRAY_BYTES</dd>
<dt>ECA_BADTYPE</dt>
<dd>The data type specified is invalid</dd>
<dt>ECA_BADSTR</dt>
<dd>Invalid string</dd>
<dt>ECA_BADCHID</dt>
<dd>Invalid channel identifier</dd>
<dt>ECA_BADCOUNT</dt>
<dd>Invalid element count requested</dd>
<dt>ECA_PUTFAIL</dt>
<dd>Channel write request failed</dd>
<dt>ECA_GETFAIL</dt>
<dd>Channel read request failed</dd>
<dt>ECA_ADDFAIL</dt>
<dd>unable to install subscription request</dd>
<dt>ECA_TIMEOUT</dt>
<dd>User specified timeout on IO operation expired</dd>
<dt>ECA_EVDISALLOW</dt>
<dd>function called was inappropriate for use within a callback
function</dd>
<dt>ECA_IODONE</dt>
<dd>IO operations have completed</dd>
<dt>ECA_IOINPROGRESS</dt>
<dd>IO operations are in progress</dd>
<dt>ECA_BADSYNCGRP</dt>
<dd>Invalid synchronous group identifier</dd>
<dt>ECA_NORDACCESS</dt>
<dd>Read access denied</dd>
<dt>ECA_NOWTACCESS</dt>
<dd>Write access denied</dd>
<dt>ECA_DISCONN</dt>
<dd>Virtual circuit disconnect"</dd>
<dt>ECA_DBLCHNL</dt>
<dd>Identical process variable name on multiple servers</dd>
<dt>ECA_EVDISALLOW</dt>
<dd>Request inappropriate within subscription (monitor) update callback</dd>
<dt>ECA_BADMONID</dt>
<dd>Bad event subscription (monitor) identifier</dd>
<dt>ECA_BADMASK</dt>
<dd>Invalid event selection mask</dd>
<dt>ECA_PUTCBINPROG</dt>
<dd>Put callback timed out</dd>
<dt>ECA_PUTCBINPROG</dt>
<dd>Put callback timed out</dd>
<dt>ECA_ANACHRONISM</dt>
<dd>Requested feature is no longer supported</dd>
<dt>ECA_NOSEARCHADDR</dt>
<dd>Empty PV search address list</dd>
<dt>ECA_NOCONVERT</dt>
<dd>No reasonable data conversion between client and server types</dd>
<dt>ECA_BADFUNCPTR</dt>
<dd>Invalid function pointer</dd>
<dt>ECA_ISATTACHED</dt>
<dd>Thread is already attached to a client context</dd>
<dt>ECA_UNAVAILINSERV</dt>
<dd>Not supported by attached service</dd>
<dt>ECA_CHANDESTROY</dt>
<dd>User destroyed channel</dd>
<dt>ECA_BADPRIORITY</dt>
<dd>Invalid channel priority</dd>
<dt>ECA_NOTTHREADED</dt>
<dd>Preemptive callback not enabled - additional threads may not join
context</dd>
<dt>ECA_16KARRAYCLIENT</dt>
<dd>Client's protocol revision does not support transfers exceeding 16k
bytes</dd>
</dl>
<p><small>$Id$
.</small></p>
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