feat(pit): add pit functions

k/pic/pit.c

@@ -0,0 +1,24 @@
+#include "io.h"
+#include "pit.h"
+
+static uint64_t counter = 0;
+
+void pit_handler(void)
+{
+    counter++;
+}
+
+void init_pit(void)
+{
+    // write to control register
+    outb(PIT_CONTROL_REG, PIT_SET_COUNTER_0 | PIT_MODE_2 | PIT_RW_LSB_MSB);
+
+    // write frequency
+    outb(PIT_COUNTER_0, DIVIDER_LO);
+    outb(PIT_COUNTER_0, DIVIDER_HI);
+}
+
+uint64_t gettick(void)
+{
+    return counter * 10;
+}

k/pic/pit.h

@@ -0,0 +1,38 @@
+#ifndef PIT_H
+#define PIT_H
+
+#define BCD_SET 0x1
+
+#define PIT_MODE_0 (0x0 << 1)
+#define PIT_MODE_1 (0x1 << 1)
+#define PIT_MODE_2 (0x2 << 1)
+#define PIT_MODE_3 (0x3 << 1)
+#define PIT_MODE_4 (0x4 << 1)
+#define PIT_MODE_5 (0x5 << 1)
+
+#define PIT_RW_SPECIAL (0x0 << 4)
+#define PIT_RW_LSB     (0x1 << 4)
+#define PIT_RW_MSB     (0x2 << 4)
+#define PIT_RW_LSB_MSB (0x3 << 4)
+
+#define PIT_SET_COUNTER_0 (0x0 << 6)
+#define PIT_SET_COUNTER_1 (0x1 << 6)
+#define PIT_SET_COUNTER_2 (0x2 << 6)
+
+// port definition
+#define PIT_COUNTER_0   0x40
+#define PIT_COUNTER_1   0x41
+#define PIT_COUNTER_2   0x42
+#define PIT_CONTROL_REG 0x43
+
+// to get 100Hz
+#define DIVIDER_LO (11931 & 0xff)
+#define DIVIDER_HI (11931 >> 8)
+
+#include <stdint.h>
+
+void pit_handler(void);
+void init_pit(void);
+uint64_t gettick(void);
+
+#endif