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x86: Add a fake IRQ7 handler to avoid spurious interrupts

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The 8259a PIC has a well known problem of generating flaky
IRQ7 interrupts. The correct solution is to always check
if an IRQ7 interrupt is real or not by probing the PIC's ISR
register. This check is only mandatory if the IRQ7 is actually
being used by the system. More importantly, the handler should
NEVER send and EOI if the interrupt was spurious.

This patch addresses this issue by implementing a fake empty
handler for this IRQ and, as stated, NOT sending the EOI.
This commit is contained in:
Jesus Sanchez-Palencia 2015-07-02 18:28:44 -03:00
parent afd9b5b0b7
commit 3b01e04379
1 changed files with 21 additions and 0 deletions
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21
cpu/x86/cpu.c
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@ -34,12 +34,28 @@
#include "interrupt.h" #include "interrupt.h"
#include "pic.h" #include "pic.h"
#define IRQ7_INT PIC_INT(7)
static void static void
double_fault_handler(struct interrupt_context context) double_fault_handler(struct interrupt_context context)
{ {
halt(); halt();
} }
/*---------------------------------------------------------------------------*/ /*---------------------------------------------------------------------------*/
static void
spurious_irq7_handler(void)
{
/*
* NOTE: Originally IRQ7 was used for the parallel port interrupts. Nowadays,
* though, it is only used if some other IRQ (i.e.: a PCIx interrupt) is
* mapped to it. In this case we will have to check the PIC ISR register in
* order to confirm this was a real interrupt.
*
* In case of a spurious interrupt, we should NEVER send an EOI here so the PIC
* doesn't trigger the next queued interrupt.
*/
}
/*---------------------------------------------------------------------------*/
void void
cpu_init(void) cpu_init(void)
{ {
@ -52,4 +68,9 @@ cpu_init(void)
SET_INTERRUPT_HANDLER(8, 1, double_fault_handler); SET_INTERRUPT_HANDLER(8, 1, double_fault_handler);
pic_init(); pic_init();
/* Set a 'fake' handler for the Spurious IRQ7 interrupts.
* Refer to http://wiki.osdev.org/PIC .
*/
SET_INTERRUPT_HANDLER(IRQ7_INT, 0, spurious_irq7_handler);
} }