RE: Interrupt doesn't make it to the 8259 on a ASUS P4PE mobo

["Richard B. Johnson" <root@chaos.analogic.com>]

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).
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