Date: Fri, 31 May 2002 09:12:56 -0700 From: Peter Wemm <peter@wemm.org> To: John Baldwin <jhb@FreeBSD.ORG> Cc: Bosko Milekic <bmilekic@unixdaemons.com>, freebsd-smp@FreeBSD.ORG, freebsd-hackers@FreeBSD.ORG, Aaro J Koskinen <akoskine@cc.helsinki.fi> Subject: Re: ICU_LEN with IO APIC Message-ID: <20020531161256.5EAFC380A@overcee.wemm.org> In-Reply-To: <XFMail.20020531100111.jhb@FreeBSD.org>
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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 - peter@wemm.org; peter@FreeBSD.org; peter@yahoo-inc.com "All of this is for nothing if we don't go to the stars" - JMS/B5 To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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