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<title>EPICS easyPVA</title>
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href="http://epics-pvdata.sourceforge.net/base.css" />
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<div class="head">
<h1>EPICS easyPVA</h1>
<!-- Maturity: Working Draft or Request for Comments, or Recommendation, and date. -->
<h2 class="nocount">EPICS V4 Working Group, Working Draft,
19-Feb-2015</h2>
<dl>
<dt>This version:</dt>
<dd><a
href="easyPVA.html">easyPVA.html
</a> </dd>
<dt>Latest version:</dt>
<dd>none</dd>
<dt>Previous version:</dt>
<dd>none</dd>
<dt>Editors:</dt>
<dd>Marty Kraimer, BNL</dd>
<dd>Matej Sekoranja, Cosylab</dd>
</dl>
<h2 class="nocount">Abstract</h2>
<p>EasyPVA (Easy PVAccess) is a software library that provides to an EPICS client programmer, a friendly
client side programming interface to the data of an EPICS based control system. It is intended
for such uses as rapid development of ad hoc programs by controls engineers, or to provide
scientists a way to directly develop analytical applications.</p>
<p>Specifically, easyPVA provides an easy interface for pvAccess, which is the
software support for high speed controls network communications used in EPICS version 4.
PvAccess provides a callback based interface, which can be hard to use.
EasyPVA provides an interface that does not require callbacks even for monitors.
</p>
<p>
EasyChannel provides many "convenience" methods to directly get and put
scalar and scalarArray data types.
Additional methods provide access to the full features of pvAccess.
</p>
<p>
EasyMultiChannel provides access to data from multiple channels as long
as each channel has a top level field named <b>value</b>.
EasyMultiChannel provides two ways to access data from multiple channels:
The first is as an NTMultiChannel. The second is as a double array.
The double array can be used if the value field of every channel is a numeric scalar.
There is code for NTMultiChannel that helps with access to more complicated data types.
</p>
<p>EasyPVA will become part of pvAccess when it is ready. </p>
<!-- last para of Abstract is boilerplate reference to EPICS -->
<p>For more information about EPICS generally, please refer to the home page of the <a
href="http://www.aps.anl.gov/epics/">Experimental Physics and Industrial
Control System</a>.</p>
<h2 class="nocount">Status of this Document and of the EasyPVA Software</h2>
<p>Under development</p>
</div> <!-- head -->
<div id="toc">
<h2 class="nocount">Table of Contents</h2>
</div>
<!-- Place what you would like in the Table of Contents, inside the contents div -->
<div id="contents" class="contents">
<hr />
<h2>Introduction</h2>
<p>EasyPVA is a synchronous API for accessing PVData via PVAccess. It provides
an interface to many of the features provided by pvData and pvAccess.</p>
<p>The EasyPVA API has the following features:</p>
<ol>
<li>Makes common requests easy to program</li>
<li>Provides full access to the pvAccess API for more demanding
applications</li>
<li>Allows efficient client side programs.</li>
</ol>
<p>The following describes the CPP version of EasyPVA.</p>
<p>This is the overview for EasyPVACPP. JavaDoc documentation is available at <a
href="./html/index.html">doxygenDoc</a></p>
<h3>Initialization</h3>
<p>A client obtains the interface to EasyPVA via the call:</p>
<pre>EasyPVA easy = EasyPVAFactory.get();</pre>
<p>The client can make this call many times, but an instance of the EastPVA interface object is
only created in the first call. This first call also
starts the PVAccess client factory.</p>
<h3>EasyPVA Overview</h3>
<p>EasyPVA creates interfaces to one of the following:</p>
<dl>
<dt>EasyChannel</dt>
<dd>This creates an interface for accessing a single channel.<br />
There are two methods for creating an EasyChannel,
with the difference being that the second
specifiers the name of the provider.
The other assumes that the provider is "pva" (pvAccess).
</dd>
<dt>EasyMultiChannel</dt>
<dd>This creates an interface for accessing a set of channels.<br />
There are multiple methods for creating an EasyMultiChannel.
The provider can be supplied or use a default of "pva".
A union for the UnionArray for accessing the value fields of each channel
can be provided or a default of variant union will be used.
</dd>
</dl>
<p>There are additional methods that allows the client to:</p>
<ol>
<li>Control how error messages are handled.</li>
<li>Control when get/put commands are sent the channel or channels.</li>
</ol>
<h3>EasyChannel Overview</h3>
<p>This interface creates Easy support for each PVAccess::Channel create
method:</p>
<dl>
<dt>EasyField</dt>
<dd>This gets the introspection interface from a channel. The
implementation provides full access to the features of
Channel::getField.</dd>
<dt>EasyProcess</dt>
<dd>This is used to process a channel. The implementation provides full
access to the features of ChannelProcess.</dd>
<dt>EasyGet</dt>
<dd>This is used to get values from a channel. The implementation allows
full access to all the features of ChannelGet. By default it asks for the
fields value, alarm, and timeStamp. If the channel has a value field then
EasyGet provides convenience methods for a scalar value and for an array
value. </dd>
<dt>EasyPut</dt>
<dd>This is used to get the current value of a channel and to put values to
a channel. The implementation allows full access to all the features of
ChannelPut. By default it asks for the field value, alarm, and timeStamp.
If the channel has a value field then EasyPut provides convenience
methods for a scalar value and for an array value. </dd>
<dt>EasyRPC</dt>
<dd>This is an interface to ChannelRPC.
The implementation allows full access to all the features of ChannelRPC.
</dd>
<dt>EasyPutGet</dt>
<dd>This is an interface to ChannelPutGet. Details TBD.</dd>
<dt>EasyMonitor</dt>
<dd>This is an interface to Monitor.
The implementation allows full access to all the features of pvAccess Monitor.
</dd>
<dt>EasyArray</dt>
<dd>This is an interface to ChannelArray. Details TBD.</dd>
<dt>EasyProcess</dt>
<dd>This is an interface to ChannelProcess. Details TBD.</dd>
</dl>
<h3>EasyMultiChannel Overview</h3>
<p>This interface creates Easy support for accessing a set of channels.
The only requirement of the channels is that each must have a top level field named value.
</p>
<dl>
<dt>EasyMultiGet</dt>
<dd>This is used to get values from a a set of channels.
The result can either be an NTMultiChannel structure or a <b>double[]</b> array.
The createGet method determines the result type.
</dd>
<dt>EasyMultiPut</dt>
<dd>This is used to get and put values from/to a set of channels.
The data supplied can either be an NTMultiChannel structure or a <b>double[]</b> array.
The createPut method determines the type.
</dd>
<dt>EasyMonitor</dt>
<dd>This is used to monitor values from a set of channels.
Each event can either be an NTMultiChannel structure or a <b>double[]</b> array.
The createMonitor method determines the data type.
</dd>
</dl>
<h2>shell</h2>
<p>Directory <b>shell</b> has the following files:</p>
<dl>
<dt>exampleDatabaseEasyPVA.zip</dt>
<dd>
When unzipped this is used to create an example IOC database.
The database has the record used by the examples are tests that come with easyPVAJava.
It uses pvDatabaseCPP to build the database.
After unzipping the file:
<pre>
cd configure
cp ExampleRELEASE.local RELEASE.local
edit RELEASE.local
cd ..
make
cd iocBoot/exampleDatabase
../../bin/&lt;arch:&gt;/exampleDatabase st.cmd
</pre>
You now have a running database.
</dd>
<dt>source</dt>
<dd>
This file creates the <b>CLASSPATH</b> required
to run the examples and tests.
You have to edit it for your environment.
</dd>
<dt>rpcServiceExample</dt>
<dd>
This starts the RPCServiceExample.
This is required by ExampleEasyRPC.
</dd>
<dt>exampleGet</dt>
<dd>
This runs ExampleGet.
</dd>
<dt>exampleGetDouble</dt>
<dd>
This runs ExampleGetDouble
</dd>
<dt>doublePut</dt>
<dd>
This runs DoublePut.
</dd>
<dt>doubleArrayPut</dt>
<dd>
This runs DoubleArrayPut
</dd>
<dt>exampleMonitor</dt>
<dd>
This runs ExampleMonitor
</dd>
<dt>exampleMonitorCallback</dt>
<dd>
This runs ExampleMonitorCallback
</dd>
<dt>exampleMultiMonitor</dt>
<dd>
This runs ExampleMultiMonitor.
It and polls every few seconds for monitor events.
It gets data as NTMultiChannel.
</dd>
<dt>exampleMultiMonitorDouble</dt>
<dd>
This runs ExampleMultiMonitorDouble.
It has an event listener for new events.
It gets data as an array of doubles.
</dd>
</dl>
<h3>Examples</h3>
<p>These are examples in package <b>org.epics.pvaccess.easyPVA.example</b>
See the source code for each example.
In order to run the examples exampleDatabaseEasyPVA must be running.
</p>
<p>There is a shell command to run each example,</p>
<h3>Tests</h3>
<p>A test directory has a number of tests for easyPVAJava.
In order to run the tests both exampleDatabaseEasyPVA and rpcServiceExample
must be running.
For now these tests are being run as eclipse unit tests.
The tests also provide examples of using EasyPVA.
</p>
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