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103 lines
2.4 KiB
C
103 lines
2.4 KiB
C
/*
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* (C) Copyright 2002
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* Daniel Engström, Omicron Ceti AB, daniel@omicron.se.
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*
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* See file CREDITS for list of people who contributed to this
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* project.
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License as
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* published by the Free Software Foundation; either version 2 of
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* the License, or (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 59 Temple Place, Suite 330, Boston,
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* MA 02111-1307 USA
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*/
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#include <common.h>
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#include <asm/io.h>
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#include <asm/i8254.h>
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#include <asm/ibmpc.h>
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#define TIMER0_VALUE 0x04aa /* 1kHz 1.9318MHz / 1000 */
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#define TIMER2_VALUE 0x0a8e /* 440Hz */
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int timer_init(void)
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{
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/* initialize timer 0 and 2
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*
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* Timer 0 is used to increment system_tick 1000 times/sec
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* Timer 1 was used for DRAM refresh in early PC's
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* Timer 2 is used to drive the speaker
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* (to stasrt a beep: write 3 to port 0x61,
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* to stop it again: write 0)
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*/
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outb (PIT_CMD_CTR0 | PIT_CMD_BOTH | PIT_CMD_MODE2,
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PIT_BASE + PIT_COMMAND);
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outb (TIMER0_VALUE & 0xff, PIT_BASE + PIT_T0);
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outb (TIMER0_VALUE >> 8, PIT_BASE + PIT_T0);
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outb (PIT_CMD_CTR2 | PIT_CMD_BOTH | PIT_CMD_MODE3,
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PIT_BASE + PIT_COMMAND);
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outb (TIMER2_VALUE & 0xff, PIT_BASE + PIT_T2);
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outb (TIMER2_VALUE >> 8, PIT_BASE + PIT_T2);
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irq_install_handler (0, timer_isr, NULL);
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unmask_irq (0);
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return 0;
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}
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static u16 read_pit(void)
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{
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u8 low;
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outb (PIT_CMD_LATCH, PIT_BASE + PIT_COMMAND);
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low = inb (PIT_BASE + PIT_T0);
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return ((inb (PIT_BASE + PIT_T0) << 8) | low);
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}
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/* this is not very exact */
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void udelay (unsigned long usec)
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{
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int counter;
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int wraps;
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if (timer_init_done)
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{
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counter = read_pit ();
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wraps = usec / 1000;
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usec = usec % 1000;
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usec *= 1194;
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usec /= 1000;
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usec += counter;
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while (usec > 1194) {
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usec -= 1194;
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wraps++;
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}
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while (1) {
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int new_count = read_pit ();
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if (((new_count < usec) && !wraps) || wraps < 0)
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break;
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if (new_count > counter)
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wraps--;
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counter = new_count;
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}
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}
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}
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