[Techtalk] Spurious kernel interrupt?

[Andrew]

Maria Blackmore wrote:

> On Thu, 29 Aug 2002, Terri Oda wrote:
> 
>> I was tailing /var/log/messages today and this popped up:
>> 
>> Aug 29 16:25:09 ostraya kernel: spurious 8259A interrupt: IRQ7.
>> 
>> Does anyone know what it means?  I did a grep -c and found that I've got 24
>> instances of spurious kernel interrupts in the file (Which was started in
>> January), if that helps.  IRQ7 isn't anything right now.
> 
> 
> Hmmm, interesting
> 
> the 8259A is the original interrupt controller used in the IBM XT, the
> very first PC, it is a PIC, or programmable interrupt controller.  
> Nothing actually contains an actual 8259A nowadays, just lots of things
> that pretend to be it, standards and all that.  A spurious interrupt is ..
> an interrupt that's spurious, that is to say unexpected, which would match
> up with what you say that nothing is on IRQ7.  This bawsically means that
> something generated an interrupt, and the PIC looked for what it was, and
> couldn't find anything, so went kind of "hmmm" and carried on.
> 
> As for what is causing it, it could be a number of things.  There could be
> interference that is causing a level on a line to go just above the
> trigger level required for an interupt, it could be a printer port that is
> enabled, but doesn't have a driver for it loaded in the linux kernel.  It
> could be another piece of hardware that is enabled, but doesn't have a
> driver loaded, a serial port, a sound card.
> 
> Some people have noted that they find this happens when they are using a
> kernel that has APIC support turned on and they are using the kernel on a
> single CPU machine that doesn't have an APIC (APIC being Advanced PIC :) -
> all multiple CPU (PC) machines have an APIC.
> 
> In any case, it will do your machine no great harm.  There will probably
> be some underlying issue that is causing this, such as the hardware
> suggestions above, or intereference, or the phase of the moon, or
> sunspots, or the fact that it is the first Saturday after first full moon
> in Winter (http://www.cs.wisc.edu/~ballard/bofh/) :)
> 
> There has been some discussion on this on the Linux Kernel Mailing List,
> where you will probably find some much more in depth discussion and
> explanation of this, archives are at
> http://www.uwsg.iu.edu/hypermail/linux/kernel/ .  I've done a quick
> search, but cursory investigation doesn't show up much more detail that I
> have gone into, though I did find hints towards an in depth thread about
> this very subject at some indeterminate point in the past.
> 
> As I said, it's nothing to worry about, and far less scary than this
> wonderful message:
> Jun 26 16:09:57 mariab kernel: lp0 on fire
> :)
> 
> For those of you who are interested, the 8259A is an 8 channel
> programmable interrupt controller, vintage of the original IBM XT era, the
> reason that modern PCs have 16 interrupts (of which you can use 15) is
> that they expanded the number of interrupts available by chaining two of
> them together via interrupt two, which is why you always see interrupt 2
> in /proc/interrupts listed as "cascade".  I would guess that many of you
> know this already, but I thought some people might find this interestin.
> 
> Have Fun
> 
> Maria
> 
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> 
   Although I, do not yet have a clue, it is interesting and one more 
step toward understanding what is in the box.

   Andrew