611x AO Fifo is taking extrememly long to fill

[gpaf]

I'm using a NI 611x card that has been working fine on previous motherboards.  I switched to a newer motherboard and things don't work very well any more.  They continue to work to some degree, but I tracked down the issue to the AO FIFO takes about 110 milliseconds to fill now 5K of data.  On the old motherboard it only took about 150 microseconds.  What is going on?  The old motherboard was PCI / PCIe with a hyperthreaded 2.4 GHz pentium with Intel 945GNT chipset and the new is a 3GHz Core2 Duo with PCI / PCIe with Intel P35+ICH9 chipset.  Anybody have any idea why the filling the AO FIFO takes about 1000x longer on the newer/faster motherboard?

[EEsRULEtheWORLD]

Certain motherboards have been found to have a higher latency than others.  These motherboards can unfortunately affect the M-Series AO DMA transfers.  There is no solution to this issue, but there are workarounds:

(1)  Implement a delay between the start of the task and the first sample:  If the problem is with the latency of the first DMA transfer as opposed to the total throughput over the PCI bus), then adding a delay before you try to write the first sample should resolve the issue.

• You could create this delay by configuring an external start trigger with the DAQmx Trigger VI. 
• You can also configure this delay with the DAQmx Trigger Property Node (Start >> More >> Delay / Delay Units).  This applies even if you don't explicitly have a start trigger configured.

(2)  Change the transfer mechanism to IRQ:  It is important to note that IRQ is typically much slower at 150 kb/s versus DMA which can achieve rates of up to 20 Mb/s. 

• You can configure your system to use IRQ by utilizing the Channel Property Node in DAQmx (Counter Input >> General Properties >> More >> Advanced >> Data Transfer and Memory >> Data Transfer Mechanism) to specify the transfer method.

(3)  Check for any BIOS updates available for your motherboard that might remedy the issue:  This is information that the manufacturer would know more about.