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Subject: DBE_PROPERTY event of Enum type in PCAS
From: "Wang Xiaoqiang (PSI)" <xiaoqiang.wang@psi.ch>
To: Epics <tech-talk@aps.anl.gov>
Date: Thu, 9 Jun 2016 19:54:05 +0000
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





Replies:
Re: DBE_PROPERTY event of Enum type in PCAS Ralph Lange

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