2 Replies Latest reply on Dec 16, 2014 3:10 PM by vikasv_56

    Capturing streaming data via EZ-USB

      My application involves an FPGA to convert a 74MHZ bitstream to a 9MB/s byte stream and send it to the EZUSB, then to a Windows7 host.


      The FPGA has minimal memory  (~16KB) for FIFO, plus the EZUSB.


      I used the streaming example to start off with, and I'm properly doing overlapped IO, in a separate high priority thread, etc. etc.


      My first attempt uses bulk, and it works when nothing is touched on the PC, but if I move/resize a window, or refresh a webpage, or look at the computer funny, the USB bus has some latency (in the 10s of mS), and the EZUSB can't offload the data quick enough and the FIFOs back up and I lose data.  NOTE:  I cannot stop the data from coming to me!


      Will moving to another USB endpoint model (interrupt end points?   isochronous?) help this problem, or am I in need of a much larger FIFO to try to smooth over the spikey latency in Windows/USB?

        • 1. Re: Capturing streaming data via EZ-USB

          To follow up, I saw another post from somebody doing high speed microframe interrupts and getting 8MB/s throughput, so that sounds positive.




          But is the issue i'm suffering from w/bulk transfers (i.e. occasionally they don't get serviced quick enough) going to be resolved by moving to interrupt endpoints?   (Again, assuming my app has a separate high priority thread using multiply queued overlapped transactions to read the data out).




          Does the kernel level driver (i.e. more real time) in windows handle the turn-around of multiple transactions?  Or is that done in the user space (i.e. less real time)?

          • 2. Re: Capturing streaming data via EZ-USB



            BULK endpoints dooesn't have dedicated bandwidth.So when you are using your PC the data rate may get decrease.




            If you use ISOC high bandwidth endpoint you will get 24MBps dedicated bandwidth.Even if you use your PC and run some other applications also there won;t be any decrease in data rate.