Date: Wed, 5 Oct 2005 12:52:12 +0930 From: "Wilkinson, Alex" <alex.wilkinson@dsto.defence.gov.au> To: freebsd-current@freebsd.org, current@freebsd.org Subject: Re: Broken MP table detected ... Message-ID: <20051005032211.GB67868@squash.dsto.defence.gov.au> In-Reply-To: <200509261611.36343.jhb@FreeBSD.org> References: <20050920004358.GA76462@squash.dsto.defence.gov.au> <200509211640.38493.jhb@FreeBSD.org> <20050923024615.GT91606@squash.dsto.defence.gov.au> <200509261611.36343.jhb@FreeBSD.org>
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0n Mon, Sep 26, 2005 at 04:11:35PM -0400, John Baldwin wrote:
>On Thursday 22 September 2005 10:46 pm, Wilkinson, Alex wrote:
>> 0n Wed, Sep 21, 2005 at 04:40:36PM -0400, John Baldwin wrote:
>> >On Monday 19 September 2005 08:55 pm, Scott Long wrote:
>> >> Wilkinson, Alex wrote:
>> >> > Can anyone tell me what the following means, and how to fix it:
>> >> >
>> >> > APIC_IO: Testing 8254 interrupt delivery
>> >> > APIC_IO: Broken MP table detected: 8254 is not connected to
>> >> > IOAPIC #0 intpin 2 APIC_IO: routing 8254 via 8259 and IOAPIC #0
>> >> > intpin 0
>> >> >
>> >> > - aW
>> >>
>> >> It means that you need to use 6.0 instead of 5.x =-) It represents
>> >> the old way that we connected the timecounters, which apparently
>> >> isn't well supported with newer amd64 boards. 6.0 solves this
>> >> problem by using a better supported mechanism.
>> >
>> >Actually, this is a 4.x method and it basically means that it has
>> > fallen back to mixed mode for IRQ0. 6.0 certainly does this better.
>> > 5.x just uses mixed mode by default.
>>
>> John, what is mixed mode ?
>
>Normally when you use the APICs, you don't use the older 8259A AT-PICs at all.
>However, the 8259A's are hooked up to pin 0 on the first I/O APIC, so if you
>enable pin 0 and enable interruput pins on the 8259As, then if they get an
>interrupt, they will forward it to the first I/O APIC which will then forward
>it to the CPUs as directed. Using both the old PICs and the APICs at the
>same time using pin 0 in the first I/O APIC is known as mixed mode. The
>reason FreeBSD uses it is that some motherboard manufacturers chose to not
>connect an IRQ0 input from the ISA timer to pin 2 on the first I/O APIC, even
>though the MP Table said that they did. The reason they could get away with
>that is that Windows didn't use IRQ0 when it used the APICs, so the
>motherboards still passed WHQL certification ok (or so I've been told).
>Linux also doesn't use IRQ0, but uses the built-in countdown periodic timer
>that each CPU has in its local APIC. In 4.x, the kernel would try to get
>IRQ0 interrupts via pin 2 on the first I/O APIC and if it didn't work, it
>printed out the message you saw and enabled mixed mode and enabled IRQ0 in
>the 8259A AT-PIC. In 5.x, we just always use mixed mode without the runtime
>test and have a hint for forcing it to not use mixed mode. In 6.x we use the
>countdown timer in the local APIC like Linux and Windows when using the APICs
>and don't use IRQ0 at all.
As usual an awesome explanation. Thanks for taking the time to explain this to me !
- aW
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