extra frame acquired in TTL Veto Only mode

[jklynch]

The xspress3 IOC was installed on the TES beamline at NSLS-II in August 2022 and again at the TES beamline in May 2023. We observe an issue in the May 2023 installation that does not seem to be present in the August 2022 installation. The issue is that when the xspress3 is in TTL Veto Only mode, a frame is acquired as soon as the acquire PV is set to 1, but before any TTL pulses have been sent. We can reproduce this through the Control System Studio screen.

For reference, the August 2022 installation was made from commit 0e8eb4ba.

[newville]

@jklynch Hm, sorry for the trouble. I am unable to test at the moment (and that may last a month).

There were some changes, but I am pretty sure I was not experiencing an initial zero-time-length frame in TTL Veto Only mode. which is what I think you are saying you see. In fact, I generally hit Start on detectors and end up with a known "hot" (dwell time too long) frame before the triggers start coming in.

I think most of the changes were about circular buffers (not used by default) and when using ERASE separately from Start. I think it should be that

set TTL_VETO_ONLY mode
set Acqure to 1
wait ~0.1 to 0.25 seconds
start sending triggers

should be all you need to do: 2 caputs to the xspress3 detectors. Well, and maybe a few more for setting up saving or ROI timeseries or HDF5 files.

[jklynch]

@newville Thanks for the information! We will look into it some more.