[PARPORT] Parport vs IDE

From: rjh@world.std.com
Date: Mon Aug 07 2000 - 13:08:29 EDT

  • Next message: Dumas Patrice: "[PARPORT] communication between computers via the parallel port"

    I've found an interesting problem with my current parport device. I've
    got a device that works reliably until I start doing IDE transfers. In
    particular, IDE write operations seem to be a problem.

    The symptom is that the peripheral appears to not see the host strobe
    for a written byte. So the PC goes into timeout on the write (which
    then leads to a problem because the device does not comply with IEEE
    1284 on host aborts, bleah). I've only caught the after failure view on
    the logic analyzer. It showed that the PC is asserting the strobe, and
    that the peripheral is not acknowledging it. I have not yet figured out
    how to trigger the analyzer on something that will show the actual
    failure, so I do not know whether strobe timings, widths, etc. are to
    spec or not.

    Does anyone have any prior experience with IDE activity interfering with
    parallel IO?

    My present test environment is to do continuous peripheral
    command/response cycles. It has a "read register" that is reasonably
    fast and I can verify that the register contents are correct. On a
    really quiescent system I let it run about 8 million cycles (each
    complete command/response takes about 250 usec). Then I did some fairly
    routine copy files around and triggered the problem within 15 seconds.
    That's about 50K read/write cycles.

    Next step is to see whether a modified retry recovery deals with this,
    but it would help if someone could suggest how IDE is causing this. I
    am assuming that an IDE interrupt hits at the wrong time and really
    messes up the timing with a block data move. This should not cause a
    problem, but somehow it seems to. This is using software implemented
    ECP logic, so the dual handshake should deal with delays.

    It is not something simple like lots of interrupts. During that 8
    million cycle test I did an ethernet ping flood of the machine (about
    3000 pings/sec 64bytes per ping, 98% echoed OK) for several minutes. No

    R Horn

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