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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.
* 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.
*
* from: Header: timerreg.h,v 1.2 93/02/28 15:08:58 mccanne Exp
* $FreeBSD$
*/
/*
* 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.
*/
/*
* Macros for specifying values to be written into a mode register.
*/
#define TIMER_REG_CNTR0 0 /* timer 0 counter port */
#define TIMER_REG_CNTR1 1 /* timer 1 counter port */
#define TIMER_REG_CNTR2 2 /* timer 2 counter port */
#define TIMER_REG_MODE 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 */
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