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

zion/CMakeLists.txt

@@ -7,6 +7,7 @@ add_executable(zion
   common/msr.cpp
   debug/debug.cpp
   interrupt/apic.cpp
+  interrupt/apic_timer.cpp
   interrupt/interrupt.cpp
   interrupt/interrupt_enter.s
   interrupt/timer.cpp

zion/interrupt/apic.cpp

@@ -6,6 +6,7 @@
 #include "common/msr.h"
 #include "common/port.h"
 #include "debug/debug.h"
+#include "interrupt/apic_timer.h"
 
 #define APIC_DEBUG 0
 
@@ -16,6 +17,10 @@ namespace {
 #define IA32_APIC_BASE_MSR_ENABLE 0x800
 
 const uint64_t kEoiOffset = 0xB0;
+const uint64_t kLvtTimerOffset = 0x320;
+const uint64_t kTimerInitOffset = 0x380;
+const uint64_t kTimerCurrOffset = 0x390;
+const uint64_t kTimerDivOffset = 0x3E0;
 
 // FIXME: parse these from madt.
 constexpr uint64_t kLApicBase = 0xFEE0'0000;
@@ -121,7 +126,7 @@ void InspectApic() {
 void EnableApic() {
   MaskPic();
   // Map Timer.
-  SetIoEntry(0x14, 0x20);
+  SetIoEntry(0x14, 0x10020);
 
   // PCI Line 1-4
   // FIXME: These should be level triggered according to spec I believe
@@ -136,4 +141,13 @@ void EnableApic() {
   InspectApic();
 }
 
+void SetLocalTimer(uint32_t init_cnt, uint64_t mode) {
+  WriteLocalReg(kTimerInitOffset, init_cnt);
+  WriteLocalReg(kLvtTimerOffset, mode | 0x21);
+}
+uint32_t GetLocalTimer() { return GetLocalReg(kTimerCurrOffset); }
+
+void UnmaskPit() { SetIoEntry(0x14, GetIoEntry(0x14) & ~(0x10000)); }
+void MaskPit() { SetIoEntry(0x14, GetIoEntry(0x14) | 0x10000); }
+
 void SignalEOI() { WriteLocalReg(kEoiOffset, 0x0); }

zion/interrupt/apic.h

@@ -1,7 +1,18 @@
 #pragma once
 
+#include <stdint.h>
+
 void InspectApic();
 
 void EnableApic();
 
+#define LAPIC_TIMER_ONESHOT 0
+#define LAPIC_TIMER_PERIODIC 1 << 17
+
+void SetLocalTimer(uint32_t init_cnt, uint64_t mode);
+uint32_t GetLocalTimer();
+
+void UnmaskPit();
+void MaskPit();
+
 void SignalEOI();

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);
+}

zion/interrupt/apic_timer.h

@@ -0,0 +1,34 @@
+#pragma once
+
+#include <stdint.h>
+
+class ApicTimer {
+ public:
+  static void Init();
+
+  // FIXME: The calibration is not currently very accurate due to time taken
+  // handling the PIT interrupts. It would probably be good to revisit this
+  // after implementing HPET.
+  void Calibrate();
+
+  void WaitCalibration() {
+    while (calculated_frequency_ == 0) {
+      asm("hlt;");
+    }
+  }
+
+ private:
+  struct Calibration {
+    uint32_t initial_measurement = 0;
+    uint32_t tick_count = 0;
+  };
+  Calibration calibration_;
+
+  uint64_t calculated_frequency_ = 0;
+
+  ApicTimer() {}
+  void StartCalibration();
+  void FinishCalibration();
+};
+
+extern ApicTimer* gApicTimer;

zion/interrupt/interrupt.cpp

@@ -5,6 +5,7 @@
 #include "common/port.h"
 #include "debug/debug.h"
 #include "interrupt/apic.h"
+#include "interrupt/apic_timer.h"
 #include "memory/kernel_heap.h"
 #include "scheduler/scheduler.h"
 
@@ -124,9 +125,15 @@ extern "C" void interrupt_page_fault(InterruptFrame* frame) {
   panic("PF");
 }
 
-uint64_t cnt = 0;
 extern "C" void isr_timer();
 extern "C" void interrupt_timer(InterruptFrame*) {
+  gApicTimer->Calibrate();
+  SignalEOI();
+}
+
+uint64_t cnt = 0;
+extern "C" void isr_apic_timer();
+extern "C" void interrupt_apic_timer(InterruptFrame*) {
   cnt++;
   if (cnt % 20 == 0) {
     if (cnt == 20) {
@@ -170,6 +177,7 @@ void InitIdt() {
   gIdt[14] = CreateDescriptor(isr_page_fault);
 
   gIdt[0x20] = CreateDescriptor(isr_timer);
+  gIdt[0x21] = CreateDescriptor(isr_apic_timer);
 
   gIdt[0x30] = CreateDescriptor(isr_pci1);
   gIdt[0x31] = CreateDescriptor(isr_pci2);

zion/interrupt/interrupt_enter.s

@@ -60,6 +60,7 @@ isr_handler protection_fault,1
 isr_handler page_fault,1
 
 isr_handler timer
+isr_handler apic_timer
 
 isr_handler pci1
 isr_handler pci2

zion/zion.cpp

@@ -3,6 +3,7 @@
 #include "boot/acpi.h"
 #include "common/gdt.h"
 #include "debug/debug.h"
+#include "interrupt/apic_timer.h"
 #include "interrupt/interrupt.h"
 #include "interrupt/timer.h"
 #include "loader/init_loader.h"
@@ -39,7 +40,10 @@ extern "C" void zion() {
   ProcessManager::Init();
   Scheduler::Init();
   // Schedule every 50ms.
-  SetFrequency(/* hertz= */ 20);
+  ApicTimer::Init();
+  asm("sti;");
+  gApicTimer->WaitCalibration();
+  asm("cli;");
 
   dbgln("[boot] Loading sys init program.");
   LoadInitProgram();