Re: ICU_LEN with IO APIC

On 31-May-2002 Bosko Milekic wrote:
> 
> On Fri, May 31, 2002 at 12:12:00PM +0300, Aaro J Koskinen wrote:
>> Hello,
>> 
>> Is there any particular reason why the number of interrupts is limited
>> to 32 on APIC systems? Is it just a conservative guess on the number of
>> interrupts anyone might want to need...?
> 
>   I'm not sure but perhaps this is historical (and now also required
>   again), but if we use a word to mask out interrupts than after 32 we
>   run out of bits.  "Who needs more than 32 interrupts anyway?!" :-)

Actually, the historical value in stable is 24 because the same 32-bit word
shares the 8 softinterrupts with 24 hardware interrupts.  I think the APIC
only has 32 interrupt pins however.

-- 

John Baldwin <[e-mail]>  <><  http://www.FreeBSD.org/~jhb/
"Power Users Use the Power to Serve!"  -  http://www.FreeBSD.org/

To Unsubscribe: send mail to [e-mail]
with "unsubscribe freebsd-smp" in the body of the message