timerreg.h

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/*-
 * Copyright (c) 1993 The Regents of the University of California.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *      This product includes software developed by the University of
 *      California, Berkeley and its contributors.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */
#ifndef __TIMERREG_H__
#define __TIMERREG_H__  1

/*
 * Register definitions for the Intel 8253 Programmable Interval Timer.
 *
 * This chip has three independent 16-bit down counters that can be
 * read on the fly.  There are three mode registers and three countdown
 * registers.  The countdown registers are addressed directly, via the
 * first three I/O ports.  The three mode registers are accessed via
 * the fourth I/O port, with two bits in the mode byte indicating the
 * register.  (Why are hardware interfaces always so braindead?).
 *
 * To write a value into the countdown register, the mode register
 * is first programmed with a command indicating the which byte of
 * the two byte register is to be modified.  The three possibilities
 * are load msb (TMR_MR_MSB), load lsb (TMR_MR_LSB), or load lsb then
 * msb (TMR_MR_BOTH).
 *
 * To read the current value ("on the fly") from the countdown register,
 * you write a "latch" command into the mode register, then read the stable
 * value from the corresponding I/O port.  For example, you write
 * TMR_MR_LATCH into the corresponding mode register.  Presumably,
 * after doing this, a write operation to the I/O port would result
 * in undefined behavior (but hopefully not fry the chip).
 * Reading in this manner has no side effects.
 *
 * The outputs of the three timers are connected as follows:
 *
 *       timer 0 -> irq 0
 *       timer 1 -> dma chan 0 (for dram refresh)
 *       timer 2 -> speaker (via keyboard controller)
 *
 * Timer 0 is used to call hardclock.
 * Timer 2 is used to generate console beeps.
 */


/*
 * Frequency of all three count-down timers; (TIMER_FREQ/freq) is the
 * appropriate count to generate a frequency of freq hz.
 */
#ifndef TIMER_FREQ
#define TIMER_FREQ      1193182
#endif
#define TIMER_DIV(x) ((TIMER_FREQ+(x)/2)/(x))

/*
 * Macros for specifying values to be written into a mode register.
 */
#define TIMER_CNTR0     (IO_TIMER1 + 0) /* timer 0 counter port */
#define TIMER_CNTR1     (IO_TIMER1 + 1) /* timer 1 counter port */
#define TIMER_CNTR2     (IO_TIMER1 + 2) /* timer 2 counter port */
#define TIMER_MODE      (IO_TIMER1 + 3) /* timer mode port */
#define         TIMER_SEL0      0x00    /* select counter 0 */
#define         TIMER_SEL1      0x40    /* select counter 1 */
#define         TIMER_SEL2      0x80    /* select counter 2 */
#define         TIMER_INTTC     0x00    /* mode 0, intr on terminal cnt */
#define         TIMER_ONESHOT   0x02    /* mode 1, one shot */
#define         TIMER_RATEGEN   0x04    /* mode 2, rate generator */
#define         TIMER_SQWAVE    0x06    /* mode 3, square wave */
#define         TIMER_SWSTROBE  0x08    /* mode 4, s/w triggered strobe */
#define         TIMER_HWSTROBE  0x0a    /* mode 5, h/w triggered strobe */
#define         TIMER_LATCH     0x00    /* latch counter for reading */
#define         TIMER_LSB       0x10    /* r/w counter LSB */
#define         TIMER_MSB       0x20    /* r/w counter MSB */
#define         TIMER_16BIT     0x30    /* r/w counter 16 bits, LSB first */
#define         TIMER_BCD       0x01    /* count in BCD */

#endif

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