2 * Copyright (c) 2008 Joshua Phillips. All rights reserved.
4 * Redistribution and use in source and binary forms, with or without
5 * modification, are permitted provided that the following conditions are
8 * 1. Redistributions of source code must retain the above copyright
9 * notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 * notice, this list of conditions and the following disclaimer in
12 * the documentation and/or other materials provided with the
15 * THIS SOFTWARE IS PROVIDED "AS IS" AND ANY EXPRESS OR IMPLIED
16 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
17 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
18 * DISCLAIMED. IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY
19 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
20 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE
21 * GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
22 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER
23 * IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
24 * OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN
25 * IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
31 #include "interrupt.h"
35 #define TIMER_FREQ 1000
41 static tick_t tick
= 0; // current tick number
42 static unsigned long freq
; // current timer frequency
49 static void timer_interrupt(int vector
, struct interrupt_stack
*is
)
52 if (preempt_on
&& (next_preempt
<= tick
)){
58 static void set_frequency(unsigned long new_freq
)
60 unsigned short divisor
;
61 divisor
= 1193180 / new_freq
;
62 freq
= (1193180LL << 32) / divisor
;
65 outb(CNT0
, divisor
>> 8);
68 void timer_sys_start(void)
71 // Timer's frequency is 1,193,180 Hz
73 outb(CNT1
, 18); // LSB only clock divisor (?)
75 set_interrupt(irq_to_int(TIMER_IRQ
), timer_interrupt
);
76 set_frequency(TIMER_FREQ
);
77 unmask_irq(TIMER_IRQ
);