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 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 78 static int timer2_running ( void ) { 79 return ((inb(PPC_PORTB) & PPCB_T2OUT) == 0); 80 } 81 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
