Experimental Physics and
Industrial Control System

Ralph Lange <[email protected]> · Fri, 10 Jun 2016 08:51:41 +0200

Hi Xiaoqiang,

It looks like you found
    https://bugs.launchpad.net/epics-base/+bug/1510955

which had been initially submitted as
    https://github.com/pyepics/pyepics/issues/40

This seems to be a PCAS issue. Further analysis and/or patches are

highly appreciated.

Thanks a lot,
~Ralph

On 09/06/2016 21:54, Wang Xiaoqiang (PSI) wrote:

Hi,

TL;DR: When DBE_PROPERTY event is posted in a PCAS application for an Enum typed PV, the client will be noticed but with the stale state strings.

As the title said, I have create an enum typed PV “MTEST:ENUM", initially with two states [ZERO, ONE], in a PCAS(py) application.
Then this is how I expand it to 3 states and send the DBE_PROPERTY event.
// pseudo code, only to show the sequence
dd = app_table.getDD(gddAppType_dbr_ctrl_enum)
dd[gddAppTypeIndex_dbr_ctrl_enum_value].put(0)
dd[gddAppTypeIndex_dbr_ctrl_enum_enums].put([‘ZERO’,’ONE’,’TWO'])
myPV.postEvent(DBE_PROPERTY, dd)

One the client, I put a monitor with type DBR_GR_ENUM and mask DBE_PROPERTY, and print the states string in the callback.
# a.py
def valueCB(epicsArgs, userArgs):
     print(epicsArgs['pv_statestrings’])

chan1 = CaChannel('MTEST:ENUM')
chan1.searchw()
chan1.add_masked_array_event(ca.DBR_GR_ENUM, None, ca.DBE_PROPERTY, valueCB)
chan1.flush_io()
while True:
     time.sleep(2)

The result is that the callback is called for the property change event, but the state string remains the same.
$ python a.py
('ZERO', 'ONE')
('ZERO', 'ONE’)
If I then run “caget -d DBR_GR_ENUM MTEST:ENUM”, it does print the changed state strings.

However if I load such a mbbo record into IOC,
record(mbbo, "MTEST:ENUM")
{
     field (ZRST, "ZERO")
     field (ONST, "ONE")
}
  and change the state string with "dbpf MTEST:ENUM.TWST TWO”, the client will receive the event with the changed state strings.
$ python a.py
('ZERO', 'ONE')
('ZERO', 'ONE', 'TWO’)

I have doubted the PCASpy implementation. So I tested the above mbbo record through the ca-gateway(2.1.0), the result is consistent with the PCASpy application. It receives the event but with the stale state strings.

The test is with Base 3.14.12.5.

Best
Xiaoqiang

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System