Measurement Computing pci-das6* timing error

• From: Derek Foreman <Derek.Foreman_at_nrc-cnrc.gc.ca>
• Date: Wed, 16 Nov 2005 15:55:42 -0600 (CST)

Hi,

(I posted this briefly a few months ago)

I'm using a measurement computing pci-das6036 card, acquiring 10 channels 
at 20khz.

Measuring the STARTSCAN signal with an oscope showed the actual sampling 
rate to be 19.997khz or so.

It looks to me like the (rather spartan) register map's note that
"ADC Pacer Frequency = Base_clock/(Divider + 3)"
for the ADC Sample interval also applies to the Delay interval.

With the following patch in place, I sample at 20khz as intended.

Anyone know if this is the right thing to do, and if it isn't... what is?

Thanks.



diff -p -u -r1.130 cb_pcidas64.c
--- comedi/drivers/cb_pcidas64.c        6 Oct 2005 17:42:02 -0000 
1.130
+++ comedi/drivers/cb_pcidas64.c        16 Nov 2005 21:03:42 -0000
_at__at_ -2369,7 +2369,7 _at__at_ static uint32_t ai_scan_counter_6xxx( co
                         / TIMER_BASE;
                 break;
         case TRIG_FOLLOW:
-               return cmd->convert_arg / TIMER_BASE;
+               return cmd->convert_arg / TIMER_BASE - 3;
                 break;
         default:
                 break;

Received on 2005-11-16Z21:55:42