/*- * SPDX-License-Identifier: BSD-3-Clause * * 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. 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 */ /* * 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 */
