Retriggerable gated counter or analog pulse trains

Question

Hi all,
I have a problem I could not resolve in the last days. It might be even a question of creativity of how to come up with a solution.
I have an external pulse train 1 at ca. 8 kHz (frequency not fully stable). With this pulse train, I want to trigger with each pulse an analog waveform. Using X-series boards, this works perfectly.
But now I want to gate this analog signal with another pulse train 2 that is much slower than the other one (pausetrig option). Theoretically, this works nicely, too. But in reality, the analog signal simply ends at the point where it is stopped by the pause trigger, whereas I want it to stop at the end point of the waveform.
Please have a look at the drawing attached
I would be really glad about any ideas on how to solve this problem.
Best regards,
Peter

Answer 1

I don't think I've ever defined both a start trigger and a pause trigger defined for the same task.  Good to know it's allowed.
Given what you've already found, the solution is to control the timing of the end of the pause trigger pulse's active state (shown here as high). 
Here's one approach:
1. Create the pause trigger pulse with a retriggerable single pulse task.  Use a minimal "low time" and "initial delay".  Set the high (active) time to be approximately (N+1) periods of your AO sample clock.  Technically, N+1 periods is a bit more than necessary, but it's sure to be enough and doesn't require research into deep details of AO timing.
2. Configure the AO task to use the pulse as *both* its start trigger (rising edge) and its pause trigger (pause when low).
Comments: this makes for a different timing diagram than you've drawn.  Each external 8 kHz pulse causes a minimally-delayed pause trigger pulse which lasts long enough to generate the full AO waveform but ends before the next 8 kHz pulse.  The choice of when to start and stop this trigger pulse will be up to your own logic and will be governed by software timing. 
   Oh dang!  That still leaves you susceptible to a partial waveform since you can't sync the software timing to occur during the desired small fraction of the 8 kHz interval with no AO waveform.
Second approach:
1. Similar to #1 above, but set the high (active) time to cover multiple 8 kHz periods and *don't* make the task retriggerable.  To get the timing right in hardware, you'll need to generate a pulse that's *approximately* the requested length, but you'll reserve the right to tweak it so the edges fall in the right place.   You'll also define your pulse in terms of the external 8 kHz signal rather than in terms of internal board time.
     Specifically, configure to generate a pulse based on units of "Ticks" using the rising edges of the external 8 kHz signal as the "source of ticks."  Set a minimal value (probably 2) for both the "low ticks" and "initial delay" inputs.  The "high ticks" setting is where you do your tweaking.
    Suppose the desired pause trigger time is 10.3 msec.  Nominally, that's 82.4 intervals of the 8 kHz external signal.  Well, just round up or down as you see fit and wire this integer # into the "high ticks" input. 
2. AO task is configured to retrigger off the external 8 kHz signal and be pause triggered by #1's counter pulse.
Comments: When you start the pause trigger pulse task, it will remain in its low idle state for the first two 8 kHz pulses.  It will go high on the 3rd pulse and then revert low on the 82nd subsequent pulse.
   Because this pulse *also* acts as a pause trigger for the AO task, you're now synced such that the AO task is paused exactly as it is being retriggered, meaning that the previous waveform must have been allowed to complete.  (The deep details of timing will prevent the AO task from generating 1 sample at this instant.)
-Kevin P