Re: [PARPORT] Timedia ASIC for PARPORT -> spurious irq 7

From: Gunther Mayer (
Date: Fri Nov 30 2001 - 14:03:10 EST

  • Next message: Tom Perkins: "Re: [PARPORT] Timedia ASIC for PARPORT -> spurious irq 7"

    Tom Perkins wrote:
    > I forced the interrupt for the slot from IRQ5 to IRQ12 with equivalent
    > results. When forced to IRQ7 everything did report solely on IRQ7.
    > I'm somewhat at a loss to explain this behavior. My first guess would be
    > a board flaw. But I fail to understand how the board could be generating
    > an interrupt on IRQ7. If it was a INTA/INTB issue I'd expect an IRQ
    > other than IRQ7. The boards INTB should show up as INTA on an adjacent
    > board right? So with the spurious interrupts showing up only on IRQ7 I
    > have to wonder if it's not a motherboard chipset quirk of some type?

    From "Harris Semiconductor 82C59A Interrupt Controller":
      If no interrupt request is present at step 4 of either sequence
      (i.e., the request was too short in duration), the 82C59A will
      issue an interrupt level 7.

    1. The irq controller sees an interrupt.
    2. The irq controller signals "there is _some_ interrupt" to the cpu.
    3. The CPU acks via INTA
    4. The irq controller looks if the irq is still there
       (and signals IRQ7 if the line is no longer active).

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