kern
view src/timer.c @ 35:06172322fb76
- made interrupt number - irq mapping macros public in intr.h
- disabled the interrupts in various vga driver functions
| author | John Tsiombikas <nuclear@member.fsf.org> |
|---|---|
| date | Thu, 09 Jun 2011 05:09:49 +0300 |
| parents | 17433fcaa563 |
| children | 2c401f69128e |
line source
1 #include <stdio.h>
2 #include "intr.h"
3 #include "asmops.h"
4 #include "timer.h"
5 #include "config.h"
7 /* frequency of the oscillator driving the 8254 timer */
8 #define OSC_FREQ_HZ 1193182
10 /* macro to divide and round to the nearest integer */
11 #define DIV_ROUND(a, b) ((a) / (b) + ((a) % (b)) / ((b) / 2))
13 /* I/O ports connected to the 8254 */
14 #define PORT_DATA0 0x40
15 #define PORT_DATA1 0x41
16 #define PORT_DATA2 0x42
17 #define PORT_CMD 0x43
19 /* command bits */
20 #define CMD_CHAN0 0
21 #define CMD_CHAN1 (1 << 6)
22 #define CMD_CHAN2 (2 << 6)
23 #define CMD_RDBACK (3 << 6)
25 #define CMD_LATCH 0
26 #define CMD_ACCESS_LOW (1 << 4)
27 #define CMD_ACCESS_HIGH (2 << 4)
28 #define CMD_ACCESS_BOTH (3 << 4)
30 #define CMD_OP_INT_TERM 0
31 #define CMD_OP_ONESHOT (1 << 1)
32 #define CMD_OP_RATE (2 << 1)
33 #define CMD_OP_SQWAVE (3 << 1)
34 #define CMD_OP_SOFT_STROBE (4 << 1)
35 #define CMD_OP_HW_STROBE (5 << 1)
37 #define CMD_MODE_BIN 0
38 #define CMD_MODE_BCD 1
41 static void intr_handler();
44 void init_timer(void)
45 {
46 /* calculate the reload count: round(osc / freq) */
47 int reload_count = DIV_ROUND(OSC_FREQ_HZ, TICK_FREQ_HZ);
49 /* set the mode to square wave for channel 0, both low
50 * and high reload count bytes will follow...
51 */
52 outb(CMD_CHAN0 | CMD_ACCESS_BOTH | CMD_OP_SQWAVE, PORT_CMD);
54 /* write the low and high bytes of the reload count to the
55 * port for channel 0
56 */
57 outb(reload_count & 0xff, PORT_DATA0);
58 outb((reload_count >> 8) & 0xff, PORT_DATA0);
60 /* set the timer interrupt handler */
61 interrupt(IRQ_TO_INTR(0), intr_handler);
62 }
64 /* This will be called by the interrupt dispatcher approximately
65 * every 1/250th of a second, so it must be extremely fast.
66 * For now, just increasing a tick counter will suffice.
67 */
68 static void intr_handler()
69 {
70 nticks++;
72 if(nticks % TICK_FREQ_HZ == 0) {
73 printf("%lu sec\n", nticks / TICK_FREQ_HZ);
74 }
75 }