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Why does it take so long to clear a task (with DMA transfer) using the PXI bus?

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I am migrating a system which used to use a PCI-6133 (8 channel simultaneous AI) and PCI-6733 (8 channel AO) to one that uses a PXI-6133 and PXI-6733 mounted in a PXI-1033 chassis.

 

In general, things seem to work (synchronized AI/AO running near the maximum rate on both devices), with the one exception that clearing an AO task on the PXI-6733 takes forever (on the order of 20-30 seconds).

 

Even when I try the sinewave generation for the PXI-6733 in the MAX test panel it takes the same amount of time to stop the task. If I switch to using interrupts as the transfer mechanism, it stops immediately.

 

I tried using the interrupt transfer mechanism on my more demanding set of synchronized tasks, but that does not produce the right behavior (even though it does not give any errors).

 

Is there any trick (or better diagnostic) to help get my tasks working with DMA under PXI that used to work fine on PCI?

 

Thanks in advance!

 

 

 

 

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Hello KKRand, 

 

That's an interesting problem.  It would be helpful if you could provide me with a bit more information.  Are you controlling your PXI devices by controller or MXI?  What hardware are you using?  While using test panels, is there a certain configuration (rate/frequency, min/max output) this occurs at or does it occur at any configuration?  Do you need to run the test panel for a certain amount of time to produce this behavior?

Patrick W.
Applications Engineer
National Instruments
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Hi Patrick,

 

I'm using a PCIe-8361 controller. The computer is a Dell T5500 workstation running Windows 7 x64. I see the problem every single time I try to clear a task running on the PXI-6733, including my example using the Measurement & Automation test panel (from the very first time I try the Sinewave Generation onward). I can try other parameters in the test panel, but I don't need to adjust anything from the defaults (e.g., Rate = 1000) to get the behavior. I will also try installing the PXI chassis in a few other computers we have here just to confirm that it's not computer specific. From your line of questions I can at least gather that there's nothing obvious (like a known bug with the PXI-6733) and that I should expect this configuration to work.

 

Thanks for your help and I'll post any other findings I obtain.

 

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You're right, it's nothing too obvious.  How many channels of AO are you using simultaneously?  The 6733 only has 3 DMA channels, so try using just one channel of AO and see if this changes anything.  

 

Another good, general troubleshooting technique is to try a different PXI slot.  

 

Finally, do you have access to a different MXI controller or an embedded controller?  I'm thinking since it worked in PCI form, the controller or MXI connection may be involved.

Patrick W.
Applications Engineer
National Instruments
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Solution
Accepted by topic author KKRand

Thanks, Patrick. I tried on a different machine (Dell T5400) and everything worked as expected. I think that the problems I experienced on the first computer were due to a conflict with a PXI driver for a different card that I did not have installed at the time of my testing (and which I didn't even realize was PXI, but it showed up as a PXI device in M&A once I put it back in, so it must have some kind of internal PCI-PXI bridge?). So in the end, pure card / slot / driver shenanigans and all seems to be good now.

 

 

 

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