Can't find application note 011 on website.

[777msmith]

Can't find Application Note 011, "DMA Fundamental on Various PC Platforms" on your website.
Can you please send me the link?

Also,  what is the packet size (chunk size) for DMA transfers on NI M series boards?
i.e. how many samples are collected into the boards FIFO buffer before DMA transfer takes place.  (How many samples (or bytes) are transferred at a time.

Is this packet size (chunk size) configurable?  If so , what is minimum value that it can take on?

Thanks,
Maurice

[Travis G.]

Hello Maurice,

I believe that the Application Note you are referring to has been removed from our website due to the fact that it was outdated with respect to Windows XP and the newer bus types used by more modern PCs.  However, I would recommend the following document for some background into the nature of how DMA data transfers affect acquisition rates of DAQ devices.

Developer Zone Tutorial: Data Acquisition Fundamentals

With regards to your second question, the size of the chunk of data sent from the onboard memory of your DAQ device to your computer system's memory is completely configurable using the NI-DAQmx driver.  When setting up a continuous data acquisition task, you can specify the size of data to transfer using the 'Samples to Read' parameter.  This parameter will instruct your DAQ device to only transfer data from its onboard memory after it has acquired a specified number of samples.  The minimum value for the 'Samples to Read' is one sample.  This is the same as doing what is called a 'hardware-timed single point acquisition', where data is acquired using the onboard clock of your DAQ device, but is transferred directly to your computer's memory after every acquisition.

I hope this helps!

Travis G
Applications Engineering
National Instruments
www.ni.com/support

[Travis G.]

Maurice,

Forgot to add this link.  It contains some interesting information about the DMA controllers on our M-Series DAQ devices.

KnowledgeBase 3G9E7C4H: How Many DMA Channels Does My M Series Data Acquisition (DAQ) Device Have?

Enjoy,
Travis G.

[777msmith]

Travis,
Thanks for all the useful information, this helps a great deal. 

Maurice