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<== Date ==> <== Thread ==>

Subject: Re: Proposed change in asyn - request for comments
From: Andrew Johnson <anj@aps.anl.gov>
To: tech-talk@aps.anl.gov
Cc: Eric Norum <wenorum@lbl.gov>
Date: Thu, 31 May 2012 10:08:17 -0500
Hi Eric,

On 2012-05-30 Eric Norum wrote:
> 
> Actually the asyn devEpics layer is simpler than described above.
> - It always sets the record TIME field from the pasynUser->timestamp in
>  the device support interrupt callback or read method then returns to
>  higher level record processing code.
>  - The record processing code then
>  overwrites the TIME field unless the TSE field is -2.

If you do this it is possible for a client that is doing ca_get operations (or 
even some other record that might have its TSEL pointing to this record's TIME 
field) to see the time set by the devEpics layer, even if the record 
subsequently overwrites the TIME field.  Since the TIME field is a structure 
with two 32-bit components it is even possible for such a client or record to 
see the seconds part of the old time-stamp and the nanoseconds from the new 
one (or vice-versa) if the interrupt happened to occur in between it reading 
the two parts.

I suspect some of them do, but I don't think device support should be updating 
*any* publicly visible record fields from inside an ISR, since it can't be 
sure that the record isn't currently locked and having field values being read 
out of it.

- Andrew
-- 
Never interrupt your enemy when he is making a mistake.
-- Napoleon Bonaparte

Replies:
Re: Proposed change in asyn - request for comments Eric Norum
References:
Proposed change in asyn - request for comments Mark Rivers
RE: Proposed change in asyn - request for comments Kim, Kukhee
Re: Proposed change in asyn - request for comments Eric Norum

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