Experimental Physics and
Industrial Control System

Hinko Kocevar <[email protected]> · Thu, 02 Jun 2011 10:42:02 +0200

Hi,

We are using pyEpics 3.1.1 for our application. The web page states that

CA connection can be performed auto-magically at ca.create_channel()

call, by calling ca.connect_channel(). This works fine. The connection

can also be postponed, by supplying the connect=False argument, the docs

also say.

We are unable to achieve the postponed connection. In the example I'm

supplying both connections are made instantly, even though the first one

has connect=False set.

Is there a way to achieve the delayed connection? We would need this to

more precisely control which PVs are actually 'enabled'/'used' in the

application ..

Example:
import epics
import time
import sys

def onConnectionChange(pvname=None, conn=None, chid=None):

 print 'ca connection status changed: ', time.time(), pvname,

conn, chid

    sys.stdout.flush()

# create channel, provide connection callback
pv1 = 'HINKS:ENV:ENV_VOLTAGE1_MONITOR'

chid1 = epics.ca.create_channel(pv1, connect=False,

callback=onConnectionChange)

# create channel, provide connection callback
pv2 = 'HINKS:ENV:ENV_VOLTAGE1_MONITOR'

chid2 = epics.ca.create_channel(pv1, connect=True,

callback=onConnectionChange)

print 'Now waiting, watching values and connection changes:'
t0 = time.time()
while time.time()-t0 < 30:
    time.sleep(0.001)

print "Exiting .."

Example output:
$ python caconnect.py

ca connection status changed: 1307003655.84

HINKS:ENV:ENV_VOLTAGE1_MONITOR True 162902648

ca connection status changed: 1307003655.84

HINKS:ENV:ENV_VOLTAGE1_MONITOR True 162902648

Now waiting, watching values and connection changes:

Thank you!

--
Hinko Kocevar
Technical support software engineer
Instrumentation Technologies
Velika pot 22, SI-5250 Solkan - Slovenia
T:+386 5 3352600, F:+386 5 3352601
mailto: [email protected]

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Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System