1 files changed, 46 insertions, 0 deletions
diff --git a/8253pit.c b/8253pit.c
new file mode 100644
index 0000000..0b82e29
--- /dev/null
+++ b/8253pit.c
@@ -0,0 +1,46 @@
+#include "types.h"
+#include "x86.h"
+#include "defs.h"
+#include "traps.h"
+
+// Register definitions for the Intel
+// 8253/8254/82C54 Programmable Interval Timer (PIT).
+
+#define	IO_TIMER1	0x040		/* 8253 Timer #1 */
+#define	IO_TIMER2	0x048		/* 8253 Timer #2 (EISA only) */
+
+//
+// Frequency of all three count-down timers; (TIMER_FREQ/freq) is the
+// appropriate count to generate a frequency of freq hz.
+
+#define	TIMER_FREQ	1193182
+#define TIMER_DIV(x)	((TIMER_FREQ+(x)/2)/(x))
+
+#define	TIMER_CNTR0	(IO_TIMER1 + 0)	/* timer 0 counter port */
+#define	TIMER_CNTR1	(IO_TIMER1 + 1)	/* timer 1 counter port */
+#define	TIMER_CNTR2	(IO_TIMER1 + 2)	/* timer 2 counter port */
+#define	TIMER_MODE	(IO_TIMER1 + 3)	/* timer mode port */
+#define		TIMER_SEL0	0x00	/* select counter 0 */
+#define		TIMER_SEL1	0x40	/* select counter 1 */
+#define		TIMER_SEL2	0x80	/* select counter 2 */
+#define		TIMER_INTTC	0x00	/* mode 0, intr on terminal cnt */
+#define		TIMER_ONESHOT	0x02	/* mode 1, one shot */
+#define		TIMER_RATEGEN	0x04	/* mode 2, rate generator */
+#define		TIMER_SQWAVE	0x06	/* mode 3, square wave */
+#define		TIMER_SWSTROBE	0x08	/* mode 4, s/w triggered strobe */
+#define		TIMER_HWSTROBE	0x0a	/* mode 5, h/w triggered strobe */
+#define		TIMER_LATCH	0x00	/* latch counter for reading */
+#define		TIMER_LSB	0x10	/* r/w counter LSB */
+#define		TIMER_MSB	0x20	/* r/w counter MSB */
+#define		TIMER_16BIT	0x30	/* r/w counter 16 bits, LSB first */
+#define		TIMER_BCD	0x01	/* count in BCD */
+
+void
+pit8253_timerinit(void)
+{
+  // initialize 8253 clock to interrupt 100 times/sec
+  outb(TIMER_MODE, TIMER_SEL0 | TIMER_RATEGEN | TIMER_16BIT);
+  outb(IO_TIMER1, TIMER_DIV(100) % 256);
+  outb(IO_TIMER1, TIMER_DIV(100) / 256);
+  irq_setmask_8259A(irq_mask_8259A & ~(1<<IRQ_TIMER));
+}