What is the fastest way of getting data?

[doenitz]

With a scanning electron microscope, I need to scan a 512*512 pixel area with a pixel repetition of 15000 (two channels), meaning averaging over 15000 measurements. Simultaneously I have to adjust the voltage output for every pixel.
I am using a 6111E Multifunction I/O board in a 800MHz P3. The whole task has do be done as fast as possible (not more than 20 minutes altogether).
What is the fastest way to get this huge amount of data with averaging and output in between? (E.g. do I use buffered read with hardware triggering or is there a faster way?)

[Filipe A.]

Doenitz;

Buffered acquisition is always faster. If you can do buffered analog input with hardware trigger, that is the preferable way to acomplish that task.
Hope this helps.
Filipe

[MagmaiKH]

Using the NI-DAQ API (not LabView) will give you a significant amount of more control over what happens and when to the data stream; which translates to a more efficient program. But you need to program in C/C++ or Delphi then. The Measurement Studio provides ActiveX controls that are like the LabView ones for C&C++ (they�re slow like the LabView ones though � not a lot you can do about the Windows GDI).

What are you trying to sample 15000 times? The 512*512 pixel field?
That�s almost 15Gigs of data! And it means you need to process data at 12.8MB/s to finish it in 20 minutes. I hope you know C, x86 assembly and MMX.

I would setup a huge circular buffer (NI-DAQ calls them �double buffers�), about 30 seconds worth or so, to use with SCAN_Start. Then I would proces
s the actual buffer the card is DMA�ing the data into with a high priority thread. Progressively sum the scan values from the 16bit buffer (the samples are only 12 bit, but the buffer should still be 16bits wide) into a secondary buffer of DWORDs the size of the screen (512*512), and you�ll need two of those, one for each channel. Once the 15000 scans are complete, convert each entry into a float divide by 15000.0f, and store it in a third buffer of floats.

If you wish to contract this out, send me an email at shannon.barber@myrealbox.com 🙂