1 /*
2 * arch/i386/core/i386_timer.c
3 *
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.
7 *
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.
12 */
13
14 FILE_LICENCE ( GPL2_OR_LATER );
15
16 #include <stddef.h>
17 #include <gpxe/timer2.h>
18 #include <gpxe/io.h>
19
20 /* Timers tick over at this rate */
21 #define TIMER2_TICKS_PER_SEC 1193180U
22
23 /* Parallel Peripheral Controller Port B */
24 #define PPC_PORTB 0x61
25
26 /* Meaning of the port bits */
27 #define PPCB_T2OUT 0x20 /* Bit 5 */
28 #define PPCB_SPKR 0x02 /* Bit 1 */
29 #define PPCB_T2GATE 0x01 /* Bit 0 */
30
31 /* Ports for the 8254 timer chip */
32 #define TIMER2_PORT 0x42
33 #define TIMER_MODE_PORT 0x43
34
35 /* Meaning of the mode bits */
36 #define TIMER0_SEL 0x00
37 #define TIMER1_SEL 0x40
38 #define TIMER2_SEL 0x80
39 #define READBACK_SEL 0xC0
40
41 #define LATCH_COUNT 0x00
42 #define LOBYTE_ACCESS 0x10
43 #define HIBYTE_ACCESS 0x20
44 #define WORD_ACCESS 0x30
45
46 #define MODE0 0x00
47 #define MODE1 0x02
48 #define MODE2 0x04
49 #define MODE3 0x06
50 #define MODE4 0x08
51 #define MODE5 0x0A
52
53 #define BINARY_COUNT 0x00
54 #define BCD_COUNT 0x01
55
load_timer2(unsigned int ticks)56 static void load_timer2 ( unsigned int ticks ) {
57 /*
58 * Now let's take care of PPC channel 2
59 *
60 * Set the Gate high, program PPC channel 2 for mode 0,
61 * (interrupt on terminal count mode), binary count,
62 * load 5 * LATCH count, (LSB and MSB) to begin countdown.
63 *
64 * Note some implementations have a bug where the high bits byte
65 * of channel 2 is ignored.
66 */
67 /* Set up the timer gate, turn off the speaker */
68 /* Set the Gate high, disable speaker */
69 outb((inb(PPC_PORTB) & ~PPCB_SPKR) | PPCB_T2GATE, PPC_PORTB);
70 /* binary, mode 0, LSB/MSB, Ch 2 */
71 outb(TIMER2_SEL|WORD_ACCESS|MODE0|BINARY_COUNT, TIMER_MODE_PORT);
72 /* LSB of ticks */
73 outb(ticks & 0xFF, TIMER2_PORT);
74 /* MSB of ticks */
75 outb(ticks >> 8, TIMER2_PORT);
76 }
77
timer2_running(void)78 static int timer2_running ( void ) {
79 return ((inb(PPC_PORTB) & PPCB_T2OUT) == 0);
80 }
81
timer2_udelay(unsigned long usecs)82 void timer2_udelay ( unsigned long usecs ) {
83 load_timer2 ( ( usecs * TIMER2_TICKS_PER_SEC ) / ( 1000 * 1000 ) );
84 while (timer2_running()) {
85 /* Do nothing */
86 }
87 }
88