handling spurious interrupts correctly

diff --git a/src/intr.c b/src/intr.c
index 5f49b87..a9bd5f1 100644 (file)
--- a/src/intr.c
+++ b/src/intr.c
@@ -60,6 +60,8 @@ static void gate_desc(desc_t *desc, uint16_t sel, uint32_t addr, int dpl, int ty
 /* defined in intr_asm.S */
 void set_idt(uint32_t addr, uint16_t limit);
 void intr_entry_default(void);
+void irq7_entry_check_spurious(void);
+void irq15_entry_check_spurious(void);
 
 /* the IDT (interrupt descriptor table) */
 static desc_t idt[256] __attribute__((aligned(8)));
@@ -90,6 +92,12 @@ void init_intr(void)
         */
 #include "intrtab.h"
 
+       /* change irq7 and irq15 to special entry points which first
+        * make sure we didn't get a spurious interrupt before proceeding
+        */
+       set_intr_entry(IRQ_TO_INTR(7), irq7_entry_check_spurious);
+       set_intr_entry(IRQ_TO_INTR(15), irq15_entry_check_spurious);
+
        /* initialize the programmable interrupt controller
         * setting up the maping of IRQs [0, 15] to interrupts [32, 47]
         */

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.