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

[Brian Gerst <bgerst@didntduck.org>]

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.

Use HZ/2 instead.  GCC doesn't optimize floating point constants to the 
same degree it does integers, because it doesn't know what mode 
(rounding, precision) the FPU is in.

--
				Brian Gerst