add PIT

src/pit.c

@@ -0,0 +1,37 @@
+#include "../include/pit.h"
+
+//https://wiki.osdev.org/Programmable_Interval_Timer
+
+/*
+Bit/s        Usage
+7            Output pin state
+6            Null count flags
+5 and 4      Access mode :
+                0 0 = Latch count value command
+                0 1 = Access mode: lobyte only
+                1 0 = Access mode: hibyte only
+                1 1 = Access mode: lobyte/hibyte
+3 to 1       Operating mode :
+                0 0 0 = Mode 0 (interrupt on terminal count)
+                0 0 1 = Mode 1 (hardware re-triggerable one-shot)
+                0 1 0 = Mode 2 (rate generator)
+                0 1 1 = Mode 3 (square wave generator)
+                1 0 0 = Mode 4 (software triggered strobe)
+                1 0 1 = Mode 5 (hardware triggered strobe)
+                1 1 0 = Mode 2 (rate generator, same as 010b)
+                1 1 1 = Mode 3 (square wave generator, same as 011b)
+0            BCD/Binary mode: 0 = 16-bit binary, 1 = four-digit BCD
+*/
+
+#define PIT_COMMAND_PORT 0x43
+#define PIT_DATA_PORT 0x40
+
+void pit_init() {
+    uint16_t frequency = 100;
+    uint8_t command = 0x36;//00110110 see above to get the idea wtf is this number
+
+    outb(PIT_COMMAND_PORT, command);
+
+    outb(PIT_DATA_PORT, (uint8_t)(frequency & 0xFF));
+    outb(PIT_DATA_PORT, (uint8_t)((frequency >> 8) & 0xFF));
+}