Re: [PARPORT] how does EPP/ECP hardware behave?

From: Tim Waugh (
Date: Thu Jan 09 2003 - 12:48:33 EST

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    On Thu, Jan 09, 2003 at 06:33:32PM +0100, Peter Asemann wrote:

    > - In SPP mode the hardware will take put the data written to the
    > data register onto the data lines and automatically set the strobe
    > signal for a predefined time. Depending on configuration, the
    > hardware will continue sending even if the peripheral did not
    > acknowledge the receiving, or wait for ACK.

    PC hardware doesn't do this. It puts the value on the data lines, and
    that's it.

    > - In ECP mode the hardware handles ECP handshake as well as RLE encoding if
    > activated. I suppose the RLE decoding of data sent from the peripheral also
    > is done in hardware?

    Yes. I've not seen any real hardware that does encoding for you, but
    of course it's possible for it to.

    > Is it, from the viewpoint of the linux drivers, so that they only
    > outb their data to the data/address register and the hardware does
    > the rest of the job?


    > What happens if something goes wrong? Does the hardware
    > send an interrupt or is the software accessing the parallel port supposed to
    > look into the status register from time to time?

    Basically it depends on the hardware. There's usually a 'something
    went wrong' bit in the status register, but its meaning can vary
    wildly from board to board.

    > I've read something about some IEEE1284 library and ppdev and other drivers
    > that might be of help?

    Yes: libieee1284 might be able to help.


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