Re: [PARPORT] ECP read - FIFO/DMA

From: Derek Bouius (dbouius@abio.com)
Date: Tue May 09 2000 - 19:00:15 EDT

  • Next message: Richard Stover: "Re: [PARPORT] ECP read - FIFO/DMA"

    I am building an ECP peripheral and am getting very slow data rates due
    to the host computer. I think it is not using the DMA correctly. I see
    the data rate to be about 1 byte / 5 usec. by using a logic analyzer on
    the port.
    I am using ECP mode in the ppdev user space driver, but with DMA, then I
    would expect to see the data sent very quickly over the port.

    How can I confirm that the ppdev is using the DMA?
    Or, if that is the data rate, what is the expected data rate if I write
    a kernel driver?

    Thanks,
    Derek

    >Since I've been working on a device driver to handle a high speed
    >camera that will produce data at very high rates I've been looking
    >at issues like this. If you have a peripheral that does follow
    >the ECP standards you shouldn't have to loose any data.
    >The way to stop data is to negotiate from reverse to forward phase
    >(from input to output). When the host sets nReverseRequest (also
    >called nInit high, the pheripheral must tri-state its data bus.
    >If the peripheral was in the middle of a data transmission it
    >must assume the data byte will be discarded by the host and
    >it stops all furthter transfers. You can then read whatever
    >is left in the fifo. nReverseRequest is bit 2 of the device
    >control register.

    >If your device doesn't adher to the ECP protocols, well...good luck.
    >I hope this helps.
    >Richard 

    --
Derek Bouius     | American Biometric Company  | Tel:(613)736-5100x281
dbouius@abio.com | 3429 Hawthorne Rd,Ottawa,ON | Fax:(613)736-1742

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