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authorrsc <rsc>2007-08-28 04:40:58 +0000
committerrsc <rsc>2007-08-28 04:40:58 +0000
commit9e82bfb04cc5644f32823fa9ec406261f05073b8 (patch)
treec1329bb47af7959a7ea3b483429529567f13f813 /timer.c
parenteae04163a758cf1fa8cc47c8668e1e769f289bc6 (diff)
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rename 8253pit.c to timer.c
Diffstat (limited to 'timer.c')
-rw-r--r--timer.c32
1 files changed, 32 insertions, 0 deletions
diff --git a/timer.c b/timer.c
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index 0000000..ba4e6c4
--- /dev/null
+++ b/timer.c
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+// Intel 8253/8254/82C54 Programmable Interval Timer (PIT).
+// Only used on uniprocessors;
+// SMP machines use the local APIC timer.
+
+#include "types.h"
+#include "defs.h"
+#include "traps.h"
+#include "x86.h"
+
+#define IO_TIMER1 0x040 // 8253 Timer #1
+
+// 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_MODE (IO_TIMER1 + 3) // timer mode port
+#define TIMER_SEL0 0x00 // select counter 0
+#define TIMER_RATEGEN 0x04 // mode 2, rate generator
+#define TIMER_16BIT 0x30 // r/w counter 16 bits, LSB first
+
+void
+timer_init(void)
+{
+ // 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_enable(IRQ_TIMER);
+}