Digital Discovery record buffer length

[ThaRev]

Beginning with Waveforms v3.8.2, the maximum sample buffer size with the Digital Discovery for any mode other than record mode is 100k. Previously up to 134M samples were available in all acquisition modes. What happened?

[attila]

Hi @ThaRev

The Repeated more is intended for timing analysis or short communication message.
The number of samples is limited since in this mode the whole capture is transferred at once. With millions of samples this would block the application, making it laggy.
Use the Record mode fore larger captures. In this Mode the data is transferred in chunks which does not block the app and it can be cancelled.

[ThaRev]

Capturing one large chunk of samples directly to DDR is largely what I'd like to do. Previously, repeated mode has worked fine but I can't find any information on record mode in the Waveforms documentation to understand exactly how it works. I assume that if data is transferred in chunks then it's closer to a streaming architecture and there is potential for missed samples between chunks at high sample rates.

The use case that repeated mode has worked well for in the past is dynamically scrubbing the timeline to set a trigger offset. Previously, if I identified a significant event that occurred say, 1.5 seconds after a trigger event, I could scrub to that position in the timeline, zoom in, set the acquisition rate and buffer size as appropriate, and re-run the acquisition to get a better look at the data. It seems that in record mode the trigger delay can only be set in a separate window as a %-age of the acquisition buffer size, which is much less convenient than in repeated mode.

 

[attila]

Hi @ThaRev

The recording on Digital Discovery is performed as normal capture in one chunk in DDR. Only the data from here to computer is transferred in smaller chunks.
Transferring 256MB over USB 2.0 takes about 8 seconds. Doing it in smaller chunks (with record) gives to feedback on the progress and possibility to cancel it.

The Record mode is for traditional Logic Analyzer usage: specify rate, samples and position. Changing the view (zoom, pan) does not affect the next capture setup.
Transferring and processing large amount of data takes time, so you capture wait and inspect the data for longer time.

The Repeated mode is for Oscilloscope like usage for timing or bit level analysis. Changing the view will affect the next capture.
It is done with less samples so processing takes less time. Lets you quickly zoom in and increase sample rate automatically to have better resolution for the next capture.
For smooth scan Screen or Shift mode we also need low amount of samples.

The next software version will let you capture max samples in Repeated mode with Digital Discovery. 

Thank you for sharing you opinion.

[leonvs]

Is there any chance upcoming Digilent Devices use USB3?

[attila]

Hi @leonvs

Yes, but I can't go into details yet.