1 files changed, 55 insertions, 0 deletions
diff --git a/kernel/drivers/pit.c b/kernel/drivers/pit.c
new file mode 100644
index 0000000..711883c
--- /dev/null
+++ b/kernel/drivers/pit.c
@@ -0,0 +1,55 @@
+#include "pit.h"
+
+#define PIT_IO_CHANNEL_0 0x40
+#define PIT_IO_MODE_COMMAND 0x43
+
+uint64_t clock_num_ms_ticks = 0;
+uint64_t pit_counter = 0;
+uint16_t hertz;
+
+uint64_t pit_num_ms(void) { return clock_num_ms_ticks; }
+
+uint16_t read_pit_count(void) {
+  uint16_t count = 0;
+
+  outb(PIT_IO_MODE_COMMAND, 0x0 /*0b00000000*/);
+
+  count = inb(PIT_IO_CHANNEL_0);
+  count |= inb(PIT_IO_CHANNEL_0) << 8;
+
+  return count;
+}
+
+void set_pit_count(uint16_t hertz) {
+  uint16_t divisor = 1193180 / hertz;
+
+  /*
+   * 0b00110110
+   *   ^^
+   * channel - 0
+   *     ^^
+   * r/w mode - LSB then MSB
+   *       ^^^
+   * mode - 3 Square Wave Mode
+   *          ^
+   * BCD - no
+   */
+  outb(PIT_IO_MODE_COMMAND, 0x36 /*0b00110110*/);
+  outb(PIT_IO_CHANNEL_0, divisor & 0xFF);
+  outb(PIT_IO_CHANNEL_0, (divisor & 0xFF00) >> 8);
+}
+
+__attribute__((interrupt)) void
+int_clock(__attribute__((unused)) struct interrupt_frame *frame) {
+  outb(0x20, 0x20);
+  pit_counter++;
+  if (pit_counter >= hertz / 1000) {
+    pit_counter = 0;
+    clock_num_ms_ticks++;
+  }
+  switch_task();
+}
+
+void pit_install(void) {
+  install_handler(int_clock, INT_32_INTERRUPT_GATE(0x0), 0x20);
+}