Multifunction DAQ

Showing results for 
Search instead for 
Did you mean: 

Delay seeing new data from correlated digital output

Hi Micaela

Here is a part of the error message, attached is the modified vi that runs at 1Mhz (not faster) on the Xeon system.
I even had to add the 2ms delay between starting the data write and starting the clock !
The answer we got and accepted was to wait for the next daqmx release.

Later on we found another "difficult" problem. When reading analog inputs at 1MHz (8 times 30 channels  and that 240 times)
we got 240 plots of 240 datapoints. This happily works ok. But... drawing a plot of this awful lot of datapoints speeds the system up!
We accept that system behaviour is not completely predictable in a hyperthreaded system (2 real but 4 hyperthreaded cpu's) but that our system speeded up from 200ms to 170ms for such amount of data was unexpected much. But of course we keep the plotting for the moment.

Original message:(Reference#5178-EX7193) NI Mseries NI-6259 too slow in Xeon system
we were trying to dump digital output data at 10MHz.this runs OK on a normal machine (e.g. DELL GX280) but sucks in a DELL Precision 670.
The reason is probably the multiprocessor architecture but also disabling the second processor in the BIOS does not help.
We tried the latest version of the DAQMX drivers (release candidate driver October 2005) but no effect.
The error message is -200016
DAQmx Wait Until<append>
<B>Task Name: </B>_unnamedTask<0>
Possible reason(s):Onboard device memory underflow.
Because of system and/or bus-bandwidth limitations,
the driver could not write data to the device fast enough to keep up with the device output rate.
Reduce your sample rate, alter the data transfer method (from interrupts to DMA),
use a product with more onboard memory, or reduce the number of programs your computer is executing concurrently.

We expect that this works on such a machine, at least has the same performance as a slower desktop.

The attached routine is not meant as an example how to write daqmx data but is the result of try and error to get it running.
The data normally sent is about 100k byte and is included in the example.
Modifying the amount of data (a lot less data)  gave also strange results (data not sent out but no error message)
If you have suggestions we will try as soon as the owner of the machine has some spare time. The system now is doing experiments.

greetings from the Netherlands
Message 11 of 14

Just curious, have you tried disabling both the second CPU and Hyperthreading? Also, have you installed the latest version of NI-DAQmx? I noticed that in your code, you were disabling regeneration. If you do not do this, do you still get the error? Finally, you said "8 times 30 channels  and that 240 times." Do you have eight of these devices in your system? Do you have a MXI setup with PXI chassis? If you are trying to stream 10MB/s of data over 8 cards, this could certainly cause issues as the maximum theoretical PCI bus bandwidth is 127MB/s. Please let us know!


Ryan Verret
Product Marketing Engineer
Signal Generators
National Instruments
0 Kudos
Message 12 of 14
Hello Ryan
Nice to hear the remarks, we indeed tried with and without hyperthreading, with and without 2 cpu's (without all did not work),
We also tried dma, no dma and all combinations of starting the dma.
The 240 samples is 8 times the same 30 channels (multiplexing one level externally) so it is only one card.
And don't forget this sytem worked nicely in a dell 740 or 720, I forgot the exact typenumber.
So moving this system to the xeon to have some more computing speed generated the IO problem.
The last version ofIO drivers were the november releases and that did not help.
Thanks for replying.
greetings from the Netherlands
Message 13 of 14

I've checked with some guys from R&D and confirmed that they are in fact looking into the cause of this issue. Hopefully, it will be fixed in a future (>8.0) version of the driver. Thank you for your patience.

Ryan Verret
Product Marketing Engineer
Signal Generators
National Instruments
0 Kudos
Message 14 of 14