Re: pyepcis does not seem to honor EPICS_CA_ADDR_LIST

[Mark Rivers via Tech-talk <tech-talk at aps.anl.gov>]

Hi Matt,

 

> I set an appropriate EPICS_CA_ADDR_LIST like: export EPICS_CA_ADDR_LIST="hipa-cagw:5062:localhost“

 

That syntax looks wrong to me.  The entries in EPICS_CA_ADDR_LIST should be separated by spaces, so it should be "hipa-cagw:5062 localhost“

 

I just tested using EPICS_CA_ADDR_LIST with pyepics on rhel7 and it worked fine.

 

My RHEL7 machine is on subnet 164.54.160.*.  There are 2 PVs

 

13IDA:m1   This is on the same 164.54.160.* subnet as the Linux machine

15IDA:m1   This is on a different subnet 164.54.162.*

 

Here I set EPICS_CA_ADDR_LIST to only be the local subnet

 

>setenv EPICS_CA_ADDR_LIST "164.54.160.255"

 

EPICS base caget can reach 13IDA:m1 but not 15IDA:m1

 

>caget 13IDA:m1

13IDA:m1                       -0.25

>caget 15IDA:m1

Channel connect timed out: '15IDA:m1' not found.

 

The same is true for Python

 

>>> import epics

>>> epics.caget('13IDA:m1')

-0.2500000000000009

>>> epics.caget('15IDA:m1')

cannot connect to 15IDA:m1

 

Now I set EPICS_CA_ADDR_LIST to also include the broadcast address of the remote 164.54.162.* network.

 

>setenv EPICS_CA_ADDR_LIST "164.54.160.255 164.54.162.255"

 

Now EPICS base caget can also reach 15IDA:m1.

 

>caget 13IDA:m1

13IDA:m1                       -0.25

>caget 15IDA:m1

15IDA:m1                       1.688e-05

 

And so can Python

 

>>> import epics

>>> epics.caget('13IDA:m1')

-0.2500000000000009

>>> epics.caget('15IDA:m1')

1.6879999999996897e-05

 

So I conclude that pyepics is handling EPICS_CA_ADDR_LIST fine.  This makes sense, because it is just using the C Channel Access library from base.

 

Mark

 

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From: Tech-talk <tech-talk-bounces at aps.anl.gov> on behalf of Koennecke Mark (PSI) via Tech-talk <tech-talk at aps.anl.gov>
Sent: Thursday, July 22, 2021 6:17 AM
To: tech-talk at aps.anl.gov
Subject: pyepcis does not seem to honor EPICS_CA_ADDR_LIST

 

Hi,

I have encountered a problem with pyepics, the most recent version on rhel7.

The trouble is: I have many PV on a local IOC, but also want to access another PV reachable
via a gateway on port 5062.

I set an appropriate EPICS_CA_ADDR_LIST like: export EPICS_CA_ADDR_LIST="hipa-cagw:5062:localhost“,
and this works to my satisfaction with the standard caget from EPICS base.

If I start python from the same terminal == same environment, load pyepics, and try to use
caget() I cannot access any PV’s at all. I have not found any reference to EPICS_CA_ADDR_LIST in the
pyepics docs. Is this a limitation or a bug? Or am I missing something?

We eventually worked around the problem by installing a calc record pointing to the PV accessible through
the gateway in our IOC and this works.  

Best Regards,

    Mark Koennecke