Enable and calibrate apic timer

src/kernel/cpu/cpu.c

@@ -26,4 +26,5 @@ void cpu_init() {
   pic_disable();
   apic_init();
   ioapic_init();
+  timer_init();
 }

src/kernel/cpu/timer.c

@@ -0,0 +1,77 @@
+#include <stdint.h>
+#include <cpu.h>
+#include <ports.h>
+
+#define PC_SPKR 0x61
+#define PIT_CH2 0x42
+#define PIT_CMD 0x43
+
+#define PIT_FREQ 1193182
+
+#define APIC_TIMER_DIVIDER 0x3E0
+#define APIC_TIMER_INIT 0x380
+#define APIC_TIMER_CURRENT 0x390
+
+volatile uint32_t apic_ticks_per_us = 1;
+
+static void pit_setup(uint8_t ms) {
+  // Disable the pc speaker output
+  uint8_t spkr = inb(PC_SPKR);
+  spkr &= ~0x1;
+  outb(PC_SPKR, spkr);
+
+  // Set up PIT for a single interrupt on CH2
+  outb(PIT_CMD, 0x80 | 0x30);
+
+  // Set up CH2 for counting down from a number of ms
+  uint64_t count = PIT_FREQ * ms/1000;
+  outb(PIT_CH2, count & 0xFF);
+  outb(PIT_CH2, (count >> 8) & 0xFF);
+}
+
+static void pit_wait() {
+
+  // Enable pc speaker
+  uint8_t spkr = inb(PC_SPKR);
+  spkr |= 0x1;
+  outb(PC_SPKR, spkr);
+
+  // Wait until there's a speaker output
+  while(!(inb(PC_SPKR) & 0x20));
+}
+
+static uint64_t calibrate_apic_timer() {
+  pit_setup(10);
+
+  APIC_REG(APIC_TIMER_DIVIDER) = 0xB;
+  APIC_REG(APIC_LVT(LVT_TIMER)) = 1<<16; // Mask
+  APIC_REG(APIC_TIMER_INIT) = 0xFFFFFFFF;
+
+  pit_wait();
+
+  uint32_t ticks = APIC_REG(APIC_TIMER_CURRENT);
+  return (0xFFFFFFFF-ticks)/10/1000;
+}
+
+void reset_apic_timer(uint64_t us) {
+  APIC_REG(APIC_TIMER_DIVIDER) = 0xB;
+  APIC_REG(APIC_TIMER_INIT) = us*apic_ticks_per_us;
+  APIC_REG(APIC_LVT(LVT_TIMER)) = 0x0 | IRQ_INTERRUPT(IRQ_TIMER);
+}
+
+volatile int ctr = 0;
+
+registers *apic_timer_handler(registers *r) {
+
+  ctr++;
+  __asm__("cli");
+  reset_apic_timer(1000);
+  irq_ack();
+  return r;
+}
+
+void timer_init() {
+  apic_ticks_per_us = calibrate_apic_timer();
+  bind_interrupt(IRQ_INTERRUPT(IRQ_TIMER), apic_timer_handler);
+  reset_apic_timer(1000);
+}

src/kernel/include/cpu.h

@@ -11,6 +11,7 @@
 #define IRQ_INTERRUPT(irq) (IRQ_BASE + (irq))
 
 #define IRQ_PS2_KBD 0x1
+#define IRQ_TIMER 0x20
 #define IRQ_SPURIOUS 0xFF
 
 #define APIC_BASE 0xFEE00000
@@ -91,4 +92,6 @@ void irq_ack();
 void irq_mask(int irq);
 void irq_unmask(int irq);
 void ioapic_init();
-void apic_init();
+
+// cpu/timer.c
+void timer_init();