HSDIO - Deterministic memory writing while generating

Question

Hello,
I am using an HSDIO card (PXI 6542) to drive a device (DUT) with a predefined fixed length continuously running waveform.
That DUT might actually benefit from some dynamic changes in the digital signals depending measurements made on the DUT itself.
Right now I just switch off the DUT and the HSDIO card, write the new waveform on the card, switch back on the DUT and the digital signal generation.
Off course that's not optimal and I'd like to modify the signal in a "live" way, while the DUT is running.
Just overwriting a waveform while it is being generated should not work smoothly due to a race condition as explained here: http://digital.ni.com/public.nsf/allkb/14CE41C9CB9F10A88625766A005CEE47
I think I found a workaround but need a confirmation on it.
Instead of just one waveform I could use 2 and select which one is being generated with the help of a trigger.
The corresponding script might look like this:
script myScript
repeat forever
if scriptTrigger0
generate waveform1
else
generate waveform2
end if
end repeat
end script
The idea is for example to generate waveform1.
Then depending on what the DUT needs I will calculate waveform2 and upload it to the HSDIO card.
My guess here is that overwriting waveform2 with data of the exact same size will not create any glitch since it is not currently being used to generate signals.
After that by using the trigger I could start to actually use waveform2. If I need further waveform adjustment I could do it by changing waveform1 while it is not being used for generation and so on by alternating which waveform is really being used.
Am I right that a waveform in memory but not currently used can be overwritten without causing glitch on another waveform that IS currently generating?
Regards,
Baptiste
Solved!
Go to Solution.

Answer 1

Hello Baptiste,
Yes, you are correct. This is a method of dynamically changing waveforms on the fly that has been used before in the past. If you generate waveform1, and download waveform2 while it is idle, it will not affect the generation of waveform1. Then, triggering via scripttrigger to waveform2, you can then download the next waveform you'd like to use to waveform1 without affecting waveform2's generation.
Kyle A.
National Instruments
High Speed Digital I/O Product Support Engineer - R&D