Re: [PARPORT] Question about 2.4.0-test1 FIFO reads

From: Tim Waugh (
Date: Mon Jul 03 2000 - 06:30:02 EDT

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    On Sun, Jul 02, 2000 at 05:13:28PM -0400, wrote:

    > 1) This assumes that the stop, turn around is fast enough to avoid a few
    > extra bytes getting into the FIFO. (The code checks for this and
    > reports an error when it happens.)

    Yes. I wonder if it works to stop it before reading from the FIFO,
    and then resume if we need more. That would close that race wouldn't

    > 2) It assumes that the peripheral is not perturbed by the host doing the
    > port turn-around before all the bytes are read.

    It assumes the peripheral is IEEE 1284 compliant, yes. There are lots
    of places where it could probably be more forgiving.

    > There must be a real motivation for this. I would not expect so much
    > code without a reason. (I've ignored some of the interrupt event
    > waiting from this since it does not seem critical to the logic. It is
    > just an optimization to avoid busy waits checking FIFO status bits.
    > Maybe this is where I missed something.)

    While writing the code I imagined a peripheral with lots of data to
    send, so I didn't want to use the FIFO (which can get filled up
    quickly) if that would cause data loss. So if the client only wants a
    few bytes, the idea is that we do it in software mode to prevent
    losing any data.

    Bear in mind that while writing it I didn't even have any proper
    hardware to test with, just the spec.


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