Re: Multiple sequencer instances undesirably sharing information

[Jure Varlec via Tech-talk <tech-talk at aps.anl.gov>]

I'd like to add a couple of points here. First, while the sequencer program options can be specified in the Makefile, they change the semantics of the program so much that it is better to declare them in the program itself; they are effectively part of it. Changing them may require a redesign of the program.

Second, and more importantly, I suggest you always specify the +s option, which enables safe mode [1]. Apart from enabling cool stuff like anonymous channels (which are much easier to use than synchronizing with event flags), it ensures your variables are only updated at well-defined times. And that's critically important! Without the +s flag, it's possible for a monitored variable to change its value at any time. You can't reason about your program logic in such a situation.

[1] https://www-csr.bessy.de/control/SoftDist/sequencer/Reference.html?highlight=option#safe-mode

Just a couple of cents from someone who observed variables change values in the middle of an action block and couldn't believe that +s was only introduced in version 2.1.

Best,

Jure

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From: Tech-talk <tech-talk-bounces at aps.anl.gov> on behalf of Marco A. Barra Montevechi Filho via Tech-talk <tech-talk at aps.anl.gov>
Sent: Wednesday, February 8, 2023 23:18
To: Pete Jemian <jemian at anl.gov>; Mark Rivers <rivers at cars.uchicago.edu>
Cc: SWC <swc at lnls.br>; Talk EPICS Tech <tech-talk at aps.anl.gov>
Subject: Re: Multiple sequencer instances undesirably sharing information

 

Caution: This email originated from outside of Cosylab.

Thanks, i was looking at this: https://www-csr.bessy.de/control/SoftDist/sequencer/Reference.html?highlight=option#option

but its also in there, so anyway there is that.

Best regards,

Marco

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From: Pete Jemian <jemian at anl.gov>
Sent: 08 February 2023 19:16
To: Marco A. Barra Montevechi Filho <marco.filho at lnls.br>; Mark Rivers <rivers at cars.uchicago.edu>
Cc: SWC <swc at lnls.br>; Talk EPICS Tech <tech-talk at aps.anl.gov>
Subject: Re: Multiple sequencer instances undesirably sharing information

 

+r is in this documentation:


https://epics.anl.gov/EpicsDocumentation/AppDevManuals/Sequencer/snl_1.9_man.html

 


On 2/8/2023 4:15 PM, Marco A. Barra Montevechi Filho wrote:
> https://epics.anl.gov/EpicsDocumentation/AppDevManuals/Sequencer/snl_1.9_man.html <https://epics.anl.gov/EpicsDocumentation/AppDevManuals/Sequencer/snl_1.9_man.html>
>

--
----------------------------------------------------------
Pete R. Jemian, Ph.D.                 <jemian at anl.gov>
Beam line Controls and Data Acquisition (BC, aka BCDA)
Advanced Photon Source,    Argonne National Laboratory
Argonne, IL  60439                    630 - 252 - 3189
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