RE: spurious 8259A interrupt

From: Maciej W. Rozycki (macro_at_ds2.pg.gda.pl)
Date: 03/23/04

  • Next message: Doug Winter: "PROBLEM: APIC on Chaintech ZNF3-150 Motherboard" 
    Date:	Tue, 23 Mar 2004 11:26:37 +0100 (CET)
To: Guennadi Liakhovetski <g.liakhovetski@gmx.de>

    On Mon, 22 Mar 2004, Guennadi Liakhovetski wrote:

    > 1) during start-up 1 message
    > spurious 8259A interrupt: IRQ7.

     That's probably a result of our local APIC setup code being a bit
    careless when seting up the ExtINTA mode. The mode is used for a
    cooperation between an 8259A PIC and a local APIC in the so-called
    virtual-wire mode.

    > 2) at run-time ERR: count increases - sometimes several per
    > second, sometimes it remains constant for some time.
    > 3) No more "spurious" messages

     It's output at most once not to clutter the log.

    > 4) I saw definitely situations, when between 2 /proc/interrupts snapshots
    > the sum of all (except the timer) interrupts was smaller, than the number
    > of errors, e.g.
    >
    > CPU0 (2nd shot)
    > 0: 36557 37638 +1081 XT-PIC timer
    > 1: 59 65 +6 XT-PIC i8042
    > 2: 0 0 XT-PIC cascade
    > 5: 0 0 XT-PIC VIA686A
    > 8: 3 3 XT-PIC rtc
    > 9: 0 0 XT-PIC acpi, uhci_hcd, uhci_hcd
    > 10: 0 0 XT-PIC eth0
    > 12: 84 84 XT-PIC i8042
    > 14: 1910 1918 +8 XT-PIC ide0
    > 15: 1 1 XT-PIC ide1
    > NMI: 18 18
    > LOC: 36460 37541 +1081
    > ERR: 36 57 +21
    >
    > ide0 + i8042 (keyboard) = 14, whereas errors increased by 21. So, if you
    > are right, than Alan's wrong (or my understanding of his statement), and
    > those spurious interrupts occur not only after real ones, or, one real
    > interrupt can produce several spurious ones.

     The PIT timer (IRQ 0 above) is edge-triggered, so it cannot cause
    spurious interrupts as a trail of real ones. Ditto for the keyboard
    controller (IRQ 1) and onboard IDE (IRQ 14). The local APIC timer
    interrupt (LOC) doesn't go through the 8259A.

     So without additonal debugging, I'd suspect noise on the interrupt lines,
    either due to a board design error or an erratum in one of devices (IRQ
    9?).

      Maciej 

    -- 
+  Maciej W. Rozycki, Technical University of Gdansk, Poland   +
+--------------------------------------------------------------+
+        e-mail: macro@ds2.pg.gda.pl, PGP key available        +
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/
  • Next message: Doug Winter: "PROBLEM: APIC on Chaintech ZNF3-150 Motherboard"

    Relevant Pages