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// The I/O APIC manages hardware interrupts for an SMP system.
// See also picirq.c.
#include "types.h"
#include "defs.h"
#include "traps.h"
#define IOAPIC 0xFEC00000 // Default physical address of IO APIC
#define REG_ID 0x00 // Register index: ID
#define REG_VER 0x01 // Register index: version
#define REG_TABLE 0x10 // Redirection table base
// The redirection table starts at REG_TABLE and uses
// two registers to configure each interrupt.
// The first (low) register in a pair contains configuration bits.
// The second (high) register contains a bitmask telling which
// CPUs can serve that interrupt.
#define INT_DISABLED 0x00010000 // Interrupt disabled
#define INT_LEVEL 0x00008000 // Level-triggered (vs edge-)
#define INT_ACTIVELOW 0x00002000 // Active low (vs high)
#define INT_LOGICAL 0x00000800 // Destination is CPU id (vs APIC ID)
volatile struct ioapic *ioapic;
// IO APIC MMIO structure: write reg, then read or write data.
struct ioapic {
uint reg;
uint pad[3];
uint data;
static uint
ioapic_read(int reg)
ioapic->reg = reg;
return ioapic->data;
static void
ioapic_write(int reg, uint data)
ioapic->reg = reg;
ioapic->data = data;
int i, id, maxintr;
ioapic = (volatile struct ioapic*)IOAPIC;
maxintr = (ioapic_read(REG_VER) >> 16) & 0xFF;
id = ioapic_read(REG_ID) >> 24;
if(id != ioapic_id)
cprintf("ioapic_init: id isn't equal to ioapic_id; not a MP\n");
// Mark all interrupts edge-triggered, active high, disabled,
// and not routed to any CPUs.
for(i = 0; i <= maxintr; i++){
ioapic_write(REG_TABLE+2*i, INT_DISABLED | (IRQ_OFFSET + i));
ioapic_write(REG_TABLE+2*i+1, 0);
ioapic_enable(int irq, int cpunum)
// Mark interrupt edge-triggered, active high,
// enabled, and routed to the given cpunum,
// which happens to be that cpu's APIC ID.
ioapic_write(REG_TABLE+2*irq, IRQ_OFFSET + irq);
ioapic_write(REG_TABLE+2*irq+1, cpunum << 24);