- From: Jack Culpepper <jack_at_email.arc.nasa.gov>
- Date: Fri, 30 Aug 2002 17:18:02 -0700
Hi all, Using the ni_pcimio driver, I am seeing something very odd: if I sample from 8 channels, and put different looking signals on each channel, it is obvious that every 'once in a while' the data from one channel shows up on another and vv. It looks something like this: 1 ================&&&======== 2 --------------------------- 3 ++++++_at__at__at_++++++++++++++++++ 4 *************************** 5 ^^^^^^^^^^^^^^^^^^^^^^^^^^^ 6 &&&&&&&&&&&&&&&&===&&&&&&&& 7 ########################### 8 _at__at__at__at__at__at_+++_at__at__at__at__at__at__at__at__at__at__at__at__at__at__at__at__at__at_ I just realized this was happening. It was probably happening all along (I've been using comedi for a couple of months now), but I just didn't notice b/c all my signal were so similar looking. I am sampling at 4000 Hz, and using a large read buffer. Does anyone have an idea of what this could be? It is almost certainly a software problem. My code is almost identical to the code in demo/cmd.c, using the prepare_cmd() function with very few other changes.. After sampling, I call comedi_to_phys() to convert the data into volts (doubles), which are immediately copied to shared memory. Thus, the code for the process sampling using comedi is extremely minimal.. I don't know what could be wrong. Thanks, Jack
Received on 2002-08-30Z23:18:02