Sporadic invalid values obtained from FlexRIO card

[JKSH]

Hello,

I'm having trouble acquiring data from my FlexRIO (PXIe-7962R + NI-5734). I'm writing custom code instead of using FIDL building blocks, because the FIDL requires a master-slave design for synchronized triggering, while I require every FlexRIO card to be able to fire the trigger.

Anyway, here is a small test case (I tried with both a 40 MHz clock and a 10 MHz clock, with the same outcomes):

FPGA

Host

While most of the output looks ok (i.e. the waveforms look like the input signals), I get many bursts of corrupted samples. I often get spikes that equal the max/min value of I16, although there are cases of non-max spikes too.

Interestingly:

• Each FlexRIO card seems to have exactly 1 misbehaving channel.
• The channel varies across cards (e.g. RIO1 gets spikes in AI0, while RIO2 gets spikes in AI3)
• When I repeatedly trigger acquisition on the same card, I see a very similar "noise shape" each time. Different cards produce different "noise shapes".
• I don't observe any spikes when I use the pre-built FIDL examples instead of my own code (perhaps I need to do some kind of synchronization??)

Screenshots below.

• The orange graphs are supposed to be all zeroes.
• The green graph is supposed to show a clean sine wave.

What might the problem be, and how can I fix it?

Thanks!

Zoomed in

 

[David-A · Accepted solution]

You need to acquire data from the 5734 in the Sample Clock domain. Reading from the AI Node in any other clock domain causes the glitching you are seeing.