2 * arch/i386/core/i386_timer.c
4 * Use the "System Timer 2" to implement the udelay callback in
5 * the BIOS timer driver. Also used to calibrate the clock rate
6 * in the RTDSC timer driver.
8 * This program is free software; you can redistribute it and/or
9 * modify it under the terms of the GNU General Public License as
10 * published by the Free Software Foundation; either version 2, or (at
11 * your option) any later version.
15 #include <gpxe/timer2.h>
18 /* Timers tick over at this rate */
19 #define TIMER2_TICKS_PER_SEC 1193180U
21 /* Parallel Peripheral Controller Port B */
22 #define PPC_PORTB 0x61
24 /* Meaning of the port bits */
25 #define PPCB_T2OUT 0x20 /* Bit 5 */
26 #define PPCB_SPKR 0x02 /* Bit 1 */
27 #define PPCB_T2GATE 0x01 /* Bit 0 */
29 /* Ports for the 8254 timer chip */
30 #define TIMER2_PORT 0x42
31 #define TIMER_MODE_PORT 0x43
33 /* Meaning of the mode bits */
34 #define TIMER0_SEL 0x00
35 #define TIMER1_SEL 0x40
36 #define TIMER2_SEL 0x80
37 #define READBACK_SEL 0xC0
39 #define LATCH_COUNT 0x00
40 #define LOBYTE_ACCESS 0x10
41 #define HIBYTE_ACCESS 0x20
42 #define WORD_ACCESS 0x30
51 #define BINARY_COUNT 0x00
52 #define BCD_COUNT 0x01
54 static void load_timer2 ( unsigned int ticks ) {
56 * Now let's take care of PPC channel 2
58 * Set the Gate high, program PPC channel 2 for mode 0,
59 * (interrupt on terminal count mode), binary count,
60 * load 5 * LATCH count, (LSB and MSB) to begin countdown.
62 * Note some implementations have a bug where the high bits byte
63 * of channel 2 is ignored.
65 /* Set up the timer gate, turn off the speaker */
66 /* Set the Gate high, disable speaker */
67 outb((inb(PPC_PORTB) & ~PPCB_SPKR) | PPCB_T2GATE, PPC_PORTB);
68 /* binary, mode 0, LSB/MSB, Ch 2 */
69 outb(TIMER2_SEL|WORD_ACCESS|MODE0|BINARY_COUNT, TIMER_MODE_PORT);
71 outb(ticks & 0xFF, TIMER2_PORT);
73 outb(ticks >> 8, TIMER2_PORT);
76 static int timer2_running ( void ) {
77 return ((inb(PPC_PORTB) & PPCB_T2OUT) == 0);
80 void timer2_udelay ( unsigned long usecs ) {
81 load_timer2 ( ( usecs * TIMER2_TICKS_PER_SEC ) / ( 1000 * 1000 ) );
82 while (timer2_running()) {