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    SubjectRE: Interrupt doesn't make it to the 8259 on a ASUS P4PE mobo
    On Tue, 15 Jul 2003, Kathy Frazier wrote:

    > Thanks for your reply, Andi.
    >
    > >> We have a proprietary PCI board installed in a (UP) system with an ASUS
    > P4PE
    > >> motherboard (uses Intel 845PE chipset). This system is running Red Hat
    > 9.0
    >
    > >Have you checked the 845 errata sheets on the Intel website?
    > >Perhaps it is some known hardware bug.
    >
    > >One thing you could try is to use Local APIC / IO APIC interrupt processing
    > >instead of 8259.
    >
    > Our hardware engineer has combed the Intel and ASUS websites, but found
    > nothing. I'll give the APIC a try and see if I get different results and
    > let you know.
    >
    > >>
    > >> /* start timer */
    > >> dmatimer.expires = jiffies + 0.5*HZ;
    >
    > >That's a serious bug. You cannot use floating point in the kernel.
    > >It will corrupt the FP state of the user process.
    >
    > HZ on the INTEL platform is 100, so this should simply add 50 to the current
    > value of jiffies. Besides, assigning the value to the unsigned int field
    > (expires) will truncate it to an integer anyway. Is there a more
    > appropriate way to handle a short timeout?

    It will truncate it at runtime.

    I suggest

    dmatimer.expires = jiffies + HZ/2;

    Also, you you need to use the time_before() macro, like

    while ( time_before(jiffies, dmatimer.expires) )
    do_something();

    ... so you don't have a timer-wrap problem during jiffie rollover if
    you haven't already done so (I don't have your source here).

    >
    > Thanks,
    > Kathy


    Cheers,
    Dick Johnson
    Penguin : Linux version 2.4.20 on an i686 machine (797.90 BogoMips).
    Why is the government concerned about the lunatic fringe? Think about it.

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