Quick Start

For testing and evaluation, it is recommended to install from pypi.org into a (disposable) virtualenv.

python -m virtualenv p4ptest
. p4ptest/bin/activate
python -m pip install -U pip
python -m pip install p4p
python -m nose p4p   # Optional: runs automatic tests

With this complete, open three terminal instances. One to run a PVA client, and two more to run PVA clients. In the first run a PVA server. Feel free to replace ‘my:pv:name’ with an arbitrary name string everywhere it occurs.

$ . p4ptest/bin/activate
$ python -m p4p.server.cli my:pv:name=int
...
INFO:p4p.server:Running server

In a second terminal run the following. If successful, the last line will end with a zero value.

$ . p4ptest/bin/activate
$ python -m p4p.client.cli monitor my:pv:name
...
my:pv:name Mon Jul  9 19:24:01 2018 0L

And finally, in a third terminal run the following. If successful, the second terminal should show the new value.

$ . p4ptest/bin/activate
$ python -m p4p.client.cli put my:pv:name=5
my:pv:name=5

Alternately, using the Client API.

from p4p.client.thread import Context
ctxt = Context('pva')
print(ctxt.get('my:pv:name'))
ctxt.put('my:pv:name', 6)
print(ctxt.get('my:pv:name'))

Troubleshooting network issues

If the preceeding didn’t work as described, there is likely a networking problem. Restart both server and client with an added argument ‘-d’. Look for lines like:

...
2018-09-27T17:00:44.164 Broadcast address #0: 10.65.15.255:5076. (not unicast)
2018-09-27T17:00:44.164 Broadcast address #1: 192.168.210.255:5076. (not unicast)
...

This indicates the two network interfaces were discovered on this host. Localhost is not included by default. If no interfaces are found, then check the system network configuration. If interfaces are found, ensure that no firewalls are applied.

By default, both client and server must share at least one discovered local broadcast address.

Non-default configuration involves the use of the $EPICS_PVA_ADDR_LIST environment variable, or configuration options specifically passed to conf= p4p.client.thread.Context(). This is considered beyond the scope of a “quick start”.