Hi XR,
I believe I understand what you're asking, but let me just repeat it to clarify: You'd like to know what happens when you set up a reference trigger for a DSA device after the task begins running in hardware, but enough time hasn't elapsed to capture all of the pretrigger samples you specified before the trigger arrives. Is this correct?
I included a visual aid that hopefully will make things clearer, wherein 10 samples are acquired. Nine (9) samples are specified as pretrigger sampled (90% of 10) and the remaining 1 sample is a post trigger sample. In the image, the earliest the reference trigger can arrive in order to capture all 9 pretrigger samples is between samples 9 and 10. This will arm the device to collect the remaining 1 sample (the 10th sample) as post-trigger.
The DSA Manual (on page 2-17, or p. 30 of the PDF file) explains what happens in this situation. The device will ignore any triggers until first the pretrigger samples fill up the buffer allocated for those samples. After the pretrigger samples are filled in that portion of the buffer, the pretrigger samples will continue to update with the most recent samples until the trigger is sensed, and the remaining portion of the buffer will be filled up with post-trigger samples.
Put another way, once the pretrigger samples are acquired, the circuitry then waits for a trigger to arm the remaining samples in the post-trigger data. So the trigger circuitry will not affect the pretrigger or post-trigger functionality until all of the pretrigger samples are taken first.
I hope this helps answer your question. Please let me know if I can help any further,
Regards,
Andrew
National Instruments
