[PARPORT] reverse channel negotiation fails under CPU load

From: Dmitri Katchalov (dmitrik@MailAndNews.com)
Date: Sun Sep 23 2001 - 23:31:51 EDT

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    I'm writing a usermode driver for my Brother MFC 4600 printer/scanner/fax.
    The driver periodically polls the device for incoming data packets
    by switching to IEEE reverse byte mode, reading the data (if any) from
    the port and then switching back to compat mode.

    It works OK as long as the computer is idle. As soon as I put any kind of
    load on a CPU (even running ps on another console)
    ioctl (parport,PPNEGOT,&IEEE_MODE_BYTE) starts failing with
    "input/output error".

    I'm running 2.4.7 kernel on P120 Toshiba laptop.
    Parport driver correctly auto-detects TRISTATE, ECP, DMA and IRQ settings
    and otherwise appears to be configured and functioning properly.

    Any ideas?


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