79 lines
3.9 KiB
C
79 lines
3.9 KiB
C
/*-
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* Copyright (c) 1993 The Regents of the University of California.
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 4. Neither the name of the University nor the names of its contributors
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* may be used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*
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* from: Header: timerreg.h,v 1.2 93/02/28 15:08:58 mccanne Exp
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* $FreeBSD$
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*/
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/*
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* Register definitions for the Intel 8253 Programmable Interval Timer.
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*
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* This chip has three independent 16-bit down counters that can be
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* read on the fly. There are three mode registers and three countdown
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* registers. The countdown registers are addressed directly, via the
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* first three I/O ports. The three mode registers are accessed via
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* the fourth I/O port, with two bits in the mode byte indicating the
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* register. (Why are hardware interfaces always so braindead?).
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*
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* To write a value into the countdown register, the mode register
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* is first programmed with a command indicating the which byte of
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* the two byte register is to be modified. The three possibilities
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* are load msb (TMR_MR_MSB), load lsb (TMR_MR_LSB), or load lsb then
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* msb (TMR_MR_BOTH).
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*
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* To read the current value ("on the fly") from the countdown register,
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* you write a "latch" command into the mode register, then read the stable
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* value from the corresponding I/O port. For example, you write
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* TMR_MR_LATCH into the corresponding mode register. Presumably,
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* after doing this, a write operation to the I/O port would result
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* in undefined behavior (but hopefully not fry the chip).
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* Reading in this manner has no side effects.
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*/
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/*
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* Macros for specifying values to be written into a mode register.
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*/
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#define TIMER_REG_CNTR0 0 /* timer 0 counter port */
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#define TIMER_REG_CNTR1 1 /* timer 1 counter port */
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#define TIMER_REG_CNTR2 2 /* timer 2 counter port */
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#define TIMER_REG_MODE 3 /* timer mode port */
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#define TIMER_SEL0 0x00 /* select counter 0 */
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#define TIMER_SEL1 0x40 /* select counter 1 */
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#define TIMER_SEL2 0x80 /* select counter 2 */
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#define TIMER_INTTC 0x00 /* mode 0, intr on terminal cnt */
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#define TIMER_ONESHOT 0x02 /* mode 1, one shot */
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#define TIMER_RATEGEN 0x04 /* mode 2, rate generator */
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#define TIMER_SQWAVE 0x06 /* mode 3, square wave */
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#define TIMER_SWSTROBE 0x08 /* mode 4, s/w triggered strobe */
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#define TIMER_HWSTROBE 0x0a /* mode 5, h/w triggered strobe */
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#define TIMER_LATCH 0x00 /* latch counter for reading */
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#define TIMER_LSB 0x10 /* r/w counter LSB */
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#define TIMER_MSB 0x20 /* r/w counter MSB */
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#define TIMER_16BIT 0x30 /* r/w counter 16 bits, LSB first */
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#define TIMER_BCD 0x01 /* count in BCD */
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