[zion] Move to using the LAPIC timer over the PIT.

zion/interrupt/apic_timer.cpp

@@ -0,0 +1,37 @@
+#include "interrupt/apic_timer.h"
+
+#include "debug/debug.h"
+#include "interrupt/apic.h"
+#include "interrupt/timer.h"
+
+ApicTimer* gApicTimer = nullptr;
+
+void ApicTimer::Init() {
+  gApicTimer = new ApicTimer();
+  gApicTimer->StartCalibration();
+}
+
+void ApicTimer::StartCalibration() {
+  SetFrequency(100);
+  SetLocalTimer(0xFFFFFFFF, 0);
+  UnmaskPit();
+}
+
+void ApicTimer::Calibrate() {
+  if (calibration_.initial_measurement == 0) {
+    calibration_.initial_measurement = GetLocalTimer();
+    return;
+  }
+  calibration_.tick_count++;
+
+  if (calibration_.tick_count == 10) {
+    calculated_frequency_ =
+        10 * (calibration_.initial_measurement - GetLocalTimer());
+    FinishCalibration();
+  }
+}
+
+void ApicTimer::FinishCalibration() {
+  MaskPit();
+  SetLocalTimer(calculated_frequency_ / 20, LAPIC_TIMER_PERIODIC);
+}