FPGA and Real Time timing

[guilio_2008]

I used the example in Labview for basic analog input for FPGA and realtime.  For lower frequency sine wave of 10Hz, the signal displayed is fine.  However, for higher frequency, 1000Hz, the siganl will not display as it should.  When I adjust the timing, it seems that I'm starting to loose chucks of the signal coming in.  The reason I'm using the example is becaues the previous VI I made gave the same results with the higher frequencies, so I went back to the basics to see if it might of been with my VI.  Is this a timing issue, is it that the module I have can't keep up with the 1000Hz, or will that example not work for what I need?  I need to have this run at 1000Hz and get all the data for calculations.  Any suggestions?

Software:

Labview 8.5

Windows XP

Hardware:

cRIO 9014

NI 9215

Thanks,

guilio

[Jeremy_B]

Hi guilio,

It looks like the FPGA will sample the 9215 at the programmed rate, and then the software loop will sample the data from the FPGA at a different rate.  However, there is no buffering between the FPGA and the real-time VI.  If you set the software loop at 100 ms and the FPGA at 1 ms, you will only get 10 samples per second in the real-time VI.  I think the example attempts to oversimplify the FPGA programming unfortunately.  If you want to get all of the samples, you will probably need to use a DMA FIFO to buffer the analog data between the FPGA and real-time (since the real-time loop will not be able to run anywhere near as fast as the FPGA).  The following links will hopefully give you some insight:

http://zone.ni.com/devzone/cda/tut/p/id/4534
http://digital.ni.com/public.nsf/allkb/8C33AC9446631A2B862573A20083CB53?OpenDocument