PyEpics 3: Epics Channel Access for Python

PyEpics is a Python interface to the EPICS Channel Access (CA) library for the EPICS control system.

The PyEpics module includes both low-level (C-like) and higher-level access (with Python objects) to the EPICS Channnel Access (CA) protocol. Python's ctypes library is used to wrap the basic CA functionality, with higher level objects on top of that basic interface. This approach has several advantages including no need for extension code written in C, better thread-safety, and easier installation on multiple platforms.

This package requires python2.6 or higher. The EPICS Channel Access library v 3.14.8 or higher is also required, with v 3.14.12 or higher being recommended. More specifically, the shared libraries libCom.so and libca.so (or Com.dll and ca.dll on Windows) are required to use this module. For Unix-like systems, these are assumed to be available (and findable by Python at runtime) on the system. For Windows, pre-built DLLs are included and installed so that no other Epics installation is required.

For installation from source, see the INSTALL file. Binary installers for Windows are available.

License

This code is distributed under the Epics Open License

Overview

Py-Epics3 provides two principle modules: ca, and pv, and functions caget(), caput(), and cainfo() for the simplest of interaction with EPICS. In addition, there are modules for Epics Motors and Alarms, autosave support via CA, and special widget classes for using EPICS PVs with wxPython.

caget(), caput() and cainfo()

The simplest interface to EPICS Channel Access provides functions caget(), caput(), and cainfo(), similar to the EZCA interface and to the EPICS-supplied command line utilities. These all take the name of an Epics Process Variable as the first argument.

>>> from epics import caget, caput, cainfo
>>> print caget('XXX:m1.VAL')
1.200
>>> caput('XXX:m1.VAL',2.30)
1
>>> cainfo('XXX.m1.VAL')
== XXX:m1.VAL  (double) ==
   value      = 2.3
   char_value = 2.3000
   count      = 1
   units      = mm
   precision  = 4
   host       = xxx.aps.anl.gov:5064
   access     = read/write
   status     = 1
   severity   = 0
   timestamp  = 1265996455.417 (2010-Feb-12 11:40:55.417)
   upper_ctrl_limit    = 200.0
   lower_ctrl_limit    = -200.0
   upper_disp_limit    = 200.0
   lower_disp_limit    = -200.0
   upper_alarm_limit   = 0.0
   lower_alarm_limit   = 0.0
   upper_warning_limit = 0.0
   lower_warning       = 0.0
   PV is monitored internally
   no user callbacks defined.
=============================

ca: Low-level Channel Access interface

The ca module provides a low-level

The general concept is that an Epics Process Variable is implemented as a python PV object, which provides the normal way to interact with Epics.

pv = EpicsCA.PV('PVName') print pv.value pv.value = new_value

For convenience, there are also procedural functions caget and caput to mimic the "Ezca" interface:

x = caget('PVName') caput('PVName', value)

A partial consequence of that design goal is that not every part of the C-level Channel Access library is implemented. Channel Access features that ARE included here are:

user callbacks: user-supplied python function(s) that are run

when a PV's value changes.

control values: a full Control DBR record can be requested. enumeration strings: enum PV types have integer or string

representation, and you get access to both.

put with wait: The PV.put() method can optionally wait until

the record is done processing (and a timeout

Features that you won't have to worry about:

connection management (unless you choose to worry about this) PV record types -- this is handled automatically.

Matt Newville <[email protected]> Last Update: 18-Apr-2016