John Baldwin wrote: > > 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.
Historically it was because ipending and friends were a 32 bit word. Even now, we have a stack of 32 bit bitfields in this area. It isn't uncommon to have 2 IO apics with 24 pins each. Fortunately there are rarely more than about 20 or so in use in total. Cheers, -Peter -- Peter Wemm - [EMAIL PROTECTED]; [EMAIL PROTECTED]; [EMAIL PROTECTED] "All of this is for nothing if we don't go to the stars" - JMS/B5 To Unsubscribe: send mail to [EMAIL PROTECTED] with "unsubscribe freebsd-hackers" in the body of the message
