handling spurious interrupts correctly

[bootcensus] / src / intr_asm.S

diff --git a/src/intr_asm.S b/src/intr_asm.S
index dcbef63..8434a8f 100644 (file)
--- a/src/intr_asm.S
+++ b/src/intr_asm.S
@@ -104,7 +104,42 @@ intr_entry_fast_timer:
        out %al, $0x20
        pop %eax
        iret
-       
+
+/* special case for IRQ 7 and IRQ 15, to catch spurious interrupts */
+       .set PIC1_CMD, 0x20
+       .set PIC2_CMD, 0xa0
+       .set OCW2_EOI, 0x20
+       .set OCW3_ISR, 0x0b
+
+       .extern intr_entry_irq7
+       .global irq7_entry_check_spurious
+irq7_entry_check_spurious:
+       push %eax
+       mov $OCW3_ISR, %al
+       out %al, $PIC1_CMD
+       in $PIC1_CMD, %al
+       and $0x80, %al
+       pop %eax
+       jnz intr_entry_irq7
+       iret
+
+       .extern intr_entry_irq15
+       .global irq15_entry_check_spurious
+irq15_entry_check_spurious:
+       push %eax
+       mov $OCW3_ISR, %al
+       out %al, $PIC2_CMD
+       in $PIC2_CMD, %al
+       and $0x80, %al
+       jnz 0f
+       # it was spurious, send EOI to master PIC and iret
+       mov $OCW2_EOI, %al
+       out %al, $PIC1_CMD
+       pop %eax
+       iret
+0:     pop %eax
+       jmp intr_entry_irq15
+
 
 /* XXX not necessary for now, just leaving it in in case it's useful
  * down the road.