Implement PIT interrupts

kernel/hal/x86_64/pit.c

@@ -0,0 +1,40 @@
+#include <stdint.h>
+#include "pit.h"
+#include "io.h"
+
+#define PIT_COUNTER0      0x40
+#define PIT_CMD           0x43
+#define PIT_CMD_BINARY    0x00
+#define PIT_CMD_BCD       0x01
+#define PIT_CMD_MODE0     0x00
+#define PIT_CMD_MODE1     0x02
+#define PIT_CMD_MODE2     0x04
+#define PIT_CMD_MODE3     0x06
+#define PIT_CMD_MODE4     0x08
+#define PIT_CMD_MODE5     0x0A
+#define PIT_CMD_LATCH     0x00
+#define PIT_CMD_RW_LOW    0x10
+#define PIT_CMD_RW_HI     0x20
+#define PIT_CMD_RW_BOTH   0x30
+#define PIT_CMD_COUNTER0  0x00
+#define PIT_CMD_COUNTER1  0x40
+#define PIT_CMD_COUNTER2  0x80
+#define PIT_CMD_READBACK  0xC0
+
+#define PIT_FREQ 1193182
+
+volatile uint32_t PIT_TICKS;
+
+void pit_init(void) {
+  uint32_t hz = 1000;
+  uint32_t div = PIT_FREQ / hz;
+  io_out8(PIT_CMD, PIT_CMD_BINARY | PIT_CMD_MODE3 | PIT_CMD_RW_BOTH | PIT_CMD_COUNTER0);
+  io_out8(PIT_COUNTER0, div);
+  io_out8(PIT_COUNTER0, div >> 8);
+}
+
+void pit_wait(uint32_t ms) {
+  uint32_t now = PIT_TICKS;
+  ++ms;
+  while (PIT_TICKS - now < ms);
+}