Re: [PARPORT] Failure to negotiate an ecp mode

Date: Thu Nov 16 2000 - 12:30:22 EST

  • Next message: Greg Peters: "Re: [PARPORT] Another 'device busy' incident"

    Is it possible for you to borrow a logic analyzer? This is admittedly a
    real long shot given their high cost, but I solved a lot of early
    problems with parallel port transactions based on having that trace of
    the genuine wire behavior.

    I've analyzed the present negotiation logic with several parallel port
    products and not found problems with it. It has revealed some problems
    with devices and with other software. For example, I had a bug where I
    caused a glitch on one line by failure to properly initialize a
    variable, which led my code to toggle one of the control lines before
    going into negotiation. The glitch was only 200ns but that was enough
    to cause the subsequent negotiation to fail. The device was not in the
    proper state for negotiation any more. (The problem was of course
    intermittent based on whatever that uninitialized variable contained. A
    good analyzer lets you program complex capture triggers to deal with
    intermittent failures like that.)

    R Horn

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