Re: Waveform Record Device Support

[emmanuel_mayssat@lynceantech.com]

On 10:06 Mon 07 Jun     , graham.cox@stfc.ac.uk wrote:
> I am integrating a turn-by-turn BPM system into EPICS and would like to
> store the raw BPM pickup data in a waveform record.  Due to the nature
> of the system, each run can result in a different number of samples for
> each BPM pickup, so the array size is unknown in advance and could
> potentially be different every run.

Given my limited experience with particle accelerators, I am just wondering what kind of system are you working with?
Storage ring, linac, ... pulsed, not pulsed?
If the waveform length is changing, it can only be because data acquisition is asynchronous.
Are you sampling CW signals? I can't think of a system that would work with those requirements.
Could you expend?

> Is it possible to resize the number of waveform record elements in my
> device support, or do I have to size the waveform record in advance for
> the maximum number of samples that could be expected.  Most of the
> examples of waveform device support I see read the nelm field and return
> this fixed amount of data via the records bptr.

Another solutions may be to use FIFO waveforms, aka compress records.
The compress record is part of epics-base.
In this case, the number of samples per channel acquired can be different, but the length of the FIFO stack can be the same.

Good luck,

-- 
Emmanuel