problem to read a fifo (compactrio)

[valais]

Hello,


I have a problem to read a fifo. I acquire sound at 20Khz on a compactrio (NI 9263). I have configured a Fifo target to host of size 2047. So normally, with a sampling of 20 KHz, my fifo must be full after about 100ms. I have attached a picture of my fpga VI.
So, in my RT VI, I read the data every 50 ms to prevent to have a full fifo. I transform the 16 bits integers into double and then want to plot the data in a waveform chart. But nothing is plot and I don't understand why. I also attached a picture of the RT VI.

Second question: In my fpga VI, I also generate a uniform white noise whith the "white noise generator". I want to generate a white noise of 0.5 V amplitude. So because the range of the NI 9263 is +/- 10 V and is coded on 16 bit, the step is 20/(2^16)=0.3051mV. So I set the amplitude to 0.5/0.3051mV=1638 to have a 0.5V at the ouptut. But when I mesure the output on an oscilloscope of always have a uniform white noise signal of +/-10V. Why?

I Hope somebody can help me.

[Jimmie_A.]

Hello,

Follow the guidelines for using the new fixed-point data type here:

http://digital.ni.com/public.nsf/allkb/672BC377EE206CC08625740F00580544?OpenDocument

http://digital.ni.com/public.nsf/allkb/1ED1B0CC0E7170FF862573620078D44B?OpenDocument

Do you get any error messages / warnings in your RT application? Please monitor these when you have applied the guidelines above in your applications.

[valais]

Thanks you for your answer Jimmie A. !

I have read the guidelines and applied the conversion to fixed points. Now it seems to work. I can transfer the datas from the fpga VI to the RT VI using the DMA FIFO. The error was that I wanted to put in directly fixed points values in the FIFO but only 16 bits integers are possible.

 I just still have a strange behaviour with the amplitude of the uniform white noise generator. I also transform the value from fixed point to 16 bits integers before going to  the amplitude terminal.  When I set an amplitude of 1, I have well 1V at the output of the NI 9263. If I set 0.7V, it still works, but if I set 0.5V, nothing at the output. As if there was a threshold to switch on the uniform white noise generator.

I attached my corrected VIs

Thanks you