buffered edge count FIFO overflow even at very low rates

[cwierzynski]

Dear Forums,

I am trying to use a PXI-6608 to timestamp the sample clock of a PXI-4498 during analog input. Because the sample rate will be on the order of 20KHz, I want to use a pulse generation task on one counter to divide it down by a factor of 1000, then use that pulse as the gate and the 10MHz clock on the 6608 as the source in a buffered edge -- I expect about 20 edges per second, which should be very manageable to retrieve over DMA.

The result is that I get error -200279 ("attempting to read samples no longer available") immediately after the vi starts, before I have retrieved even one count.

This is my first stab at using DAQmx for counter/timer instead of the old DAQ drivers, so I'm sure I've done something wrong, but I can't figure out what.

I've attached the vi if that helps.

Thanks!

Cas

[Doug_L._Bear]

It appears that you have your gate and source backwards.  The sample clock should be ctr0internaloutput and the count edges terminal should be the 10 MHz clock.  You are getting the buffer overflow error because the FIFO on the card is only 2 samples and at 10 MHz these are being rewritten was faster than a computer could possible pull them off the card.

[Doug_L._Bear · Accepted solution]

It appears that you have your gate and source backwards.  The sample clock should be ctr0internaloutput and the count edges terminal should be the 10 MHz clock.  You are getting the buffer overflow error because the FIFO on the card is only 2 samples and at 10 MHz these are being rewritten was faster than a computer could possible pull them off the card.

[cwierzynski]

Bingo! Thanks so much. I wish the DAQmx docs were more clear on this. The docs refer to source, gate, etc., but the vi's don't.

Anyway, thanks again. This is why we love the NI forums! CW