WIP - pit timer

kernel/drivers/pit.c

@@ -0,0 +1,78 @@
+#include <timer.h>
+#include <int.h>
+#include <pit.h>
+#include <debug.h>
+#include <ports.h>
+#include <apic.h>
+#include <stdint.h>
+
+#define PIT_CH0 0x40
+#define PIT_CH2 0x42
+#define PIT_CMD 0x43
+
+#define PIT_USE_CH0 0x00
+#define PIT_USE_CH2 0x80
+#define PIT_RW_LOHI 0x30
+#define PIT_MODE(M) ((M)<<1)
+
+#define PIT_FREQ 1193182
+
+#define CH2_PORT 0x61
+#define CH2_ENABLE 0x01
+#define CH2_OUT 0x20
+
+
+void delay(uint8_t ms)
+{
+  // Turn off channel 2
+  uint8_t ch2 = inb(CH2_PORT);
+  ch2 &= ~CH2_ENABLE;
+  outb(CH2_PORT, ch2);
+
+  // Set up a countdown on channel 2
+  outb(PIT_CMD, PIT_USE_CH2 | PIT_RW_LOHI | PIT_MODE(0));
+  uint16_t count = PIT_FREQ * ms/1000;
+  outb(PIT_CH2, count & 0xFF);
+  outb(PIT_CH2, (count >> 8) & 0xFF);
+
+  // Turn on channel 2
+  ch2 |= CH2_ENABLE;
+  outb(CH2_PORT, ch2);
+
+  // Busy wait (Ultimately, we'll only use this a few times during boot)
+  while(!(inb(CH2_PORT) & CH2_OUT));
+}
+
+void pit_delay(uint32_t ms)
+{
+  while(ms > 50)
+  {
+    delay(50);
+    ms -= 50;
+  }
+  if(ms)
+    delay(ms);
+}
+
+uint64_t system_ticks = 0;
+registers_t *timer_tick(registers_t *r)
+{
+  apic_ack();
+  system_ticks ++;
+  return r;
+}
+
+uint64_t get_ticks()
+{
+  return system_ticks;
+}
+
+void pit_init()
+{
+  register_int_handler(IRQ_INT(IRQ_TIMER), timer_tick);
+  outb(PIT_CMD, PIT_USE_CH0 | PIT_RW_LOHI | PIT_MODE(3));
+  uint16_t count = PIT_FREQ/TICK_FREQ;
+  outb(PIT_CH0, (count & 0xFF));
+  outb(PIT_CH0, (count >> 8));
+  IRQ_UNMASK(IRQ_TIMER);
+}