Real Time P2P Stream from Digitizer to FPGA

[ndittrich89]

Hi everybody,

I am quite new to LabView and I am currently trying to get my hardware setup running including a PXIe-1082 Reg, a  NI5122 Digitizer and a 7966R FPGA with a NI 6587 front module.

For a simple test I generate a square wave with an external function generator which is connected to the digitizers input and depending on a threshold I want to either write 0x0000 or 0xFFFF on the NI6587 Output.

The communication between the Digitizer and the FPGA is implemented using a P2P Stream and the general comunication between the two cards seems to work.

However if I look at the input and output signal on the scope, I can see that there is quite a big delay between the input rising edge of the square signal and my output of the NI6587 (around 6.5us). My later application requires a much faster response.

The digitizer is supposed to run at 100MHz and the FPGA which is the reader should run at 125MHz.

Does anyone have a clue what could be my problem?

Thanks in advance.

[A.Rohde]

That seems like valid numbers you are measuring. The bottleneck in your case is the latency introduced by P2P streaming.

"Peer-to-peer transfers are designed to have a very low latency, but it will vary depending on the system configuration.  When streaming only through FIFOs and the PCIe bus the typical latency is around 2-4 μs, though this will likely have occasional an spike into the tens of μs due to other bus traffic.  When streaming from a digitizer we can usually expect around 5 μs of latency and when streaming to an arbitrary waveform generator around 10-20 μs of latency due to onboard buffering."

http://www.ni.com/white-paper/10801/en/

Ran into a similar issue when trying to create a radar jamming system.

Edit: If you want to solve your problem faster you need to avoid the P2P streaming by handeling both input and output on the same FPGA card and adapter module. So you need to chose a FAM which both meets the desired inputs and outputs. You can find one that suits the example you describe above with Digitizer input and digital output, but I'm guessing that using the FlexRIO as a DO is only preliminary?  

Best Regards

Anders Rohde