Subject: |
[Bug 1824277] Re: Regression in calcout setting constant links at runtime |
From: |
Ben Franksen via Core-talk <[email protected]> |
To: |
[email protected] |
Date: |
Tue, 23 Apr 2019 16:33:23 -0000 |
My immediate reaction was the same as Ralph's: if we agree that this is
desired behavior then it should apply to all input links in a generic
manner, independent of record support and not requiring special
processing. I am not familiar with the internal workings of how writing
to a link field is implemented, but given that redirection to another PV
works, I guess it shouldn't be too hard to make it work for numeric
constants?
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https://bugs.launchpad.net/bugs/1824277
Title:
Regression in calcout setting constant links at runtime
Status in EPICS Base:
In Progress
Status in EPICS Base 7.0 series:
In Progress
Bug description:
With the 3.15 branch, writing a literal number to a calcout.INP[A-L]
field causes the corresponding [A-L] field to be set to that number.
This works because the calcout record marks the INP fields as
special(SPC_MOD) and the calcout::special() routine calls
recGblInitConstantLink() to initialize the corresponding [A-L] field
from the new link string. I suspect that a number of the synApps
record types (transform, scalc, acalc etc.) probably use this same
technique.
Keenan Lang reported that this doesn't currently work on the 7.0
branch; the value in the [A-L] field doesn't change, which I have
confirmed.
This use of special() to reinitialize constant links is unusual,
normally putting a literal into a link field after record
initialization has no effect, but someone who worked on the calcout
record discovered this way to get it to work.
I think I know what's going on and how to fix it (change
dbPutFieldLink() to call dbAddLink() before the second call to
dbPutSpecial()), but I need to check that this won't break other
cases.
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