Having worked with EPICS for several years now and having built
device support modules for several classes of records, I was amazed to
discover that I had no real comprehension of how alarm conditions
detected by device support (usually device access errors) were handled
by output style records -- analog output, long output, etc.. For input
style records, device support usually sets the UDF (undefined value)
field to zero and record support senses this condition and sets the
(UDF_ALARM, INVALID_ALARM) condition.
Output style records, although they also have the UDF field, do not
appear to use it to communicate a device failure from device support
to record support. It seems only to be used only in the closed-loop mode
to report a failure to obtain a value from the desired output link
(DOL).
So, how does record support detect that an access failure has
occurred during a write to an output device and propagate that
information to an interested CA client? Is record support expected to
call recGblSetSevr directly? If so, why was this not done for input
style records as well? Unfortunately, neither the chapter on record
support or the chapter on device support in the "Application
Developers Guide" offer any guidance on this question.
Fritz
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- Re: Error reporting from device support for output style records Benjamin Franksen
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