Re: DB CA link to PROC field

[Tim Mooney <mooney@aps.anl.gov>]

Andrew Johnson wrote:
> On Tuesday 14 July 2009 17:53:25 Benjamin Franksen wrote:
> > On Dienstag, 14. Juli 2009, Tim Mooney wrote:
> > > Benjamin Franksen wrote:
> > > > I get this message on the iocsh (base is 3.14.8.2):
> > > >
> > > > dbCaTask ca_array_put Channel write request failed
> > > > OTERMPCGP:cmdRmp has DB CA link to OTERMPCGP:colStRmp.PROC
> > > Ben,  I get that same error message when I use a CA link (from any
> > > record) to
> > > process a  record whose processing results in an error.  If your
> > > situation is
> > > like mine, OTERMPCGP:colStRmp should be in some kind of alarm.
> > Interesting. I'll check this. The message is a bit misleading (if this is
> > indeed what causes it), to me it suggests that I have somehow misconfigured
> > the link.
>
> I agree the message is misleading.  It occurs because any error status 
> returned by device support is passed back up the call chain and is returned 
> by the record type's process() routine, by dbProcess(), then by dbPutField(). 
> db_put_field converts it to a 0 or -1 value and results in the channel access 
> server reporting a write error to the client, which in this case is the dbCa 
> link where your error message came from.
>
> I would be interested in any thoughts on whereabouts in the above chain we 
> should clear any error status from device support.  I suspect it should be 
> the record type's responsibility once it has put the record into an alarm 
> state (thus handling and reporting the error), but I could be persuaded 
> otherwise.
>
> - Andrew

I think it's a great thing to have a message identifying the record whose
CA link caused the processing that failed.  I think a less generic error
message would be an improvement.  People expect an error message to say
what's wrong; the message "<record> has a DB CA link..." gives context for
the previous message, but I read it as implying something wrong with the link.
For me, it would be clearer if the message said something like "An error
occurred while <record A> was writing, via a DB CA link, to <record B>".

--
Tim Mooney (mooney@aps.anl.gov) (630)252-5417
Beamline Controls & Data Acquisition Group
Advanced Photon Source, Argonne National Lab.