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<title>EPICS R3.14 Channel Access Reference Manual</title>
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<hr>
<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;">BESSY</span></p>
<p><span style="font-size: xx-small; font-weight:lighter;">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 Elektronenspeicherringgesellschaft für
Synchrotronstrahlung.</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>
</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_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_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="#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="#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_get</a></li>
<li><a href="#ca_sg_put">ca_sg_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>15.0</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 longer CA timeout, default is 1.0 second</td>
</tr>
<tr>
<td>-c</td>
<td>Asynchronous get (use ca_get_callback instead of ca_get)</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></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></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 longer CA timeout, default is 1.0 second</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). Default: va</td>
</tr>
<tr>
<td></td>
<td><strong>Timestamps:</strong></td>
</tr>
<tr>
<td>Default:</td>
<td>Print absolute timestamps (as reported by CA)</td>
</tr>
<tr>
<td>-r</td>
<td>Relative timestamps (time elapsed since start of program)</td>
</tr>
<tr>
<td>-i</td>
<td>Incremental timestamps (time elapsed since last update)</td>
</tr>
<tr>
<td>-I</td>
<td>Incremental timestamps (time elapsed since last update for this
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></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></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 longer CA timeout, default is 1.0 second</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>
</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 longer CA timeout, default is 1.0 second</td>
</tr>
<tr>
<td>-s &lt;level&gt;</td>
<td>Call ca_client_status with the specified interest level</td>
</tr>
</tbody>
</table>
<p></p>
<h2><a name="Troublesho">Troubleshooting</a></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>Be advised that any user created threads that might have attached
themselves to the CA context must of course stop using it prior to its being
destroyed.</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. If a connection
is lost and then resumed outstanding ca_array_put  or ca_put  requests are
not automatically reissued following reconnect, and no additional
notification are provided to the user for each put request.</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. If unsuccessful the
call back function is invoked indicating bad status. If the channel
disconnects before a put callback request can be completed, then the client's
call back function is called with bad status, but this does not guarantee
that the server did not receive and process the request before the
disconnect.</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>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>
<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
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 get
callback request can be completed, then the clients call back function is
called with bad 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>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>
<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_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>
</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>
<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 ( 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.</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.</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>
</body>
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