Create a detector that can write out frames without interrupting acquisition

[DominicOram]

On i15-1 we have a few optical cameras that are used for diagnostics e.g. quickly check the sample is mounted etc. They are constantly acquiring so that we can view the live feed of them. We would like to take a one off snapshot of the camera to put into LIMS.

After discussing with @coretl the best way to do this is probably a new detector class that, when trigger_and_read is called will write a frame with the writer (in this case a tiff writer) without changing the acquisition state of the detector (assuming it is already acquiring).

Acceptance Criteria

• There is a detector I can use to take an image from an already acquiring detector without interrupting the acquisition.

[jwlodek]

Would the ContAcqAreaDetector class not cover this use case? We use it to do exactly what you describe.

ophyd-async/src/ophyd_async/epics/adcore/_detector.py

Line 72 in b50a75c

class ContAcqDetector(AreaDetector[ADBaseIO]):

[DominicOram]

Maybe, it assumes a CircularBuffer, which we don't always have in the chain but could add. I will try it out first, thank you!

[coretl]

My comments on slack:

• There is a ADContAcqTriggerLogic that makes sure the camera is Acquiring, you should probably use that
• There is an ADContAcqArmLogic that uses a circular buffer plugin just as a way to send N frames to a file writer, you could use that in conjunction with an ADMultipartDataLogic to write serially numbered TIFFs
• Alternatively you could make a new ADSingleDataLogic that implements prepare_single to do what you describe above

[DominicOram]

Thanks both. I tested this using the old ContAcqAreaDetector and it works well, only issue is that the first frame after changing the file name does not get written to disk, subsequent ones are fine. I suspect some race condition on the setup. I assume you haven't seen that @jwlodek?

[jwlodek]

Hmmm, I don't think I've seen that, but I can try and reproduce.

[DominicOram]

Hmmm, I don't think I've seen that, but I can try and reproduce.

Happy to keep digging my side, was only checking it didn't ring any bells.