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High speed USB chip?

Discussion in 'Electronic Design' started by Ancient_Hacker, Mar 20, 2007.

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  1. Let's say I have a flash A/D putting out a byte every 100nsec or so.

    Is there some simple chip that will take this data and send it to a
    PC thru a USB-2 port?

    hoping... Hoping.....
     
  2. linnix

    linnix Guest

    Very difficult to get 80 Mb/s through USB.
     
  3. Jim Thompson

    Jim Thompson Guest

    Ehhh?

    "Hi-Speed USB mode is capable of ... 480Mbits/second."

    ...Jim Thompson
     
  4. linnix

    linnix Guest

    But chopped into 64 byte chunks and host enabled signalings.
    A missed timing can delay the communications by msecs.
    You need very good host hardware and firmware control on the PC side.

    In theory, you can send 50 mpeg streams over usb (480/9).
    I have not seen too many device with more than 1 stream.
     
  5. Joel Kolstad

    Joel Kolstad Guest

    Well, it's true, you can't use crap USB chipsets and lousy drives, but the
    GNURadio guys routinely sustain ~256Mbps over USB with decent quality hardware
    and software; I believe I've heard them say that realistically the USB 2.0
    limit is around ~320Mbps (40MBps).

    80Mbps should be no problem.

    Granted, I wouldn't stick this data acquisition device on the same bus as the
    one you have a web cam, audio device, mouse, keyboard, etc. on -- I'd give it
    a USB controller of its very own.
     
  6. Donald

    Donald Guest

    480M(bits)/sec / 8 bits per byte = 60M(bytes)/sec

    without any overhead.

    It would be easier with a TCP connection.

    donald
     
  7. linnix

    linnix Guest

    Or crapy window drivers. I hate to disappoint the CEO of Seagate,
    but I can't watch smooth porn on my super-fast usb hard drive.
    So, the effective rate is probably less than 9 Mb/s.

    480 Mb/s usb is like saying:
    Vista is fine with less than 1G ram.
     
  8. Cypress has some high speed USB enabled microcoontrollers that allows a data
    stream to be directly routed to the USB engine, see for example the EZUSB
    FX2LP (CY7C68014A ), data throughput is claimed to be 53Mbyte/s, which
    should be ok for your application.

    Cheers,
     
  9. Hawker

    Hawker Guest

    We are using the Cypress FX2 series parts, as someone else mentioned,
    for several projects.
    The FIFOs are a bit small so we often have to use an external FIFO.
    For my current project I have one bolted to CPLD and external SRAM for a
    sorta FIFO.

    Note for USB2 the theoretical maximum is 480M BITS/Sec. So that is 60M
    Bytes per sec. In reality 80% is about all you can do or around
    50mBytes per sec (Cypress claims a bit better though). Your project is 8
    x (100nS^-1) or 80mBytes per sec. Not doable sustained, Perhaps cached
    locally and sent later?

    Hawker
     
  10. Er. You are out by a factor of eight. He is pulling one byte every
    100nSec.
    Total just 10MB/sec.
    Perfectly doable.

    Best Wishes
     
  11. Joel Kolstad

    Joel Kolstad Guest

    Umm... shouldn't that be 80Mbits per second? He wanted to sample one bytes
    every 100nS = 10 million samples/sec = 10Mbytes/sec = 80Mbps?
     
  12. The second question though is using 'm', not 'M'. Normally 'b' is bits,
    'B' is bytes, 'm' is milli, and 'M' is mega. If he only wanted 80mBits, it
    could be done using RS232 serial!...
    The stupid thing is just how easy this type of slip is. I sent a post
    myself to 'Hawker', and managed to generate the right answer, but type
    'mSec', instead of 'nSec'....
    It is a big danger of using the 'prefix' letters.

    Best Wishes
     
  13. Hawker

    Hawker Guest

    Yes as Roger and you pointed out I goofed.
    That is what I get for only half paying attention to what I am doing.
    100nS-1 = 10M/bytes *8 = 80mBits per second.
    So this will fit no problem I blew it.

    Hawker
     
  14. joseph2k

    joseph2k Guest

    Only on a dedicated single device USB controller. Protocol overhead and
    protocol timing limitations matter.
     
  15. These guys :
    https://www.quickusb.com/index.htm?target=dept_13.html
    do a module based on the Cypress chip which comes with driver software to make USB2 comms fairly
    painless.
    However you might need to add a fifo between the ADC and the USB interface to guarantee no data
    loss.
     
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