PCI 6024E GPCTR data lost

[karpesh]

On my PCI 6024 card I’m using both General Purpose Counters for buffered measuring (single buffer, not continuous) of period of TTL signal. Each buffer consist of about 20000 points. Input SOURCE of each counter internally “connected” to 20 MHz generator. Both GATE inputs connected to same measured signal.
If frequency of measured impulses not exceeded 10-13 kHz, then all works right, output arrays is identical with each other. But if frequency exceeded 13 kHz (for WinXP) or 25 kHz (for Win 98) then resulted arrays is different. At that common form of received curves is similar to each other, but the same values of measured period stands in this arrays on different places. If draw it on the diagram, then positions of value
s in one array as if “compressed” with other array.
I think, that it can be therefore the card can not transmit received data to computer in time, that’s why some data loose.
Am I right, or the reason of descripted is different? How I can solve this problem?
Sorry for bad English…

[rgharrison]

Hi karpesh,

My suspicion is that it is because of the limitation that the PCI-6024E DAQ board only has 1 DMA channel. Typically, there are 2 transfer methods for buffered operations; DMA or Interrupts. DMA is much faster since it does not need to interrupt the processor and can transfer a block of data directly from the card to memory. Interrupts on the other hand must transfer each data point one at a time and must interrupt the processor. I suspect that you are losing some datapoints with the counter using Interrupts. This is not so much a problem on E Series boards that have 3 DMA channels since each counter can use a DMA channel.

Possible solutions would be to remove all non-essential hardware using interrupts. Also, if you close all your programs
that are running except for the data acquisition program it will free up processor resources. Basically, you will want to free up as much processor time as possible so that an interrupt will not be missed. Another option is of course to upgrade your computer or upgrade your E Series board to one that has 3 DMA channels.

Anyway, hope that helps. Have a good day.

Ron
Applications Engineering
National Instruments