The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)


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FreeBSD/Linux Kernel Cross Reference
sys/dev/ic/i8253reg.h

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    1 /*-
    2  * Copyright (c) 1993 The Regents of the University of California.
    3  * All rights reserved.
    4  *
    5  * Redistribution and use in source and binary forms, with or without
    6  * modification, are permitted provided that the following conditions
    7  * are met:
    8  * 1. Redistributions of source code must retain the above copyright
    9  *    notice, this list of conditions and the following disclaimer.
   10  * 2. Redistributions in binary form must reproduce the above copyright
   11  *    notice, this list of conditions and the following disclaimer in the
   12  *    documentation and/or other materials provided with the distribution.
   13  * 4. Neither the name of the University nor the names of its contributors
   14  *    may be used to endorse or promote products derived from this software
   15  *    without specific prior written permission.
   16  *
   17  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
   18  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   19  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   20  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   21  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   22  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   23  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   24  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   25  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   26  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   27  * SUCH DAMAGE.
   28  *
   29  *      from: Header: timerreg.h,v 1.2 93/02/28 15:08:58 mccanne Exp
   30  * $FreeBSD: releng/6.2/sys/dev/ic/i8253reg.h 146215 2005-05-14 10:26:31Z nyan $
   31  */
   32 
   33 /*
   34  * Register definitions for the Intel 8253 Programmable Interval Timer.
   35  *
   36  * This chip has three independent 16-bit down counters that can be
   37  * read on the fly.  There are three mode registers and three countdown
   38  * registers.  The countdown registers are addressed directly, via the
   39  * first three I/O ports.  The three mode registers are accessed via
   40  * the fourth I/O port, with two bits in the mode byte indicating the
   41  * register.  (Why are hardware interfaces always so braindead?).
   42  *
   43  * To write a value into the countdown register, the mode register
   44  * is first programmed with a command indicating the which byte of
   45  * the two byte register is to be modified.  The three possibilities
   46  * are load msb (TMR_MR_MSB), load lsb (TMR_MR_LSB), or load lsb then
   47  * msb (TMR_MR_BOTH).
   48  *
   49  * To read the current value ("on the fly") from the countdown register,
   50  * you write a "latch" command into the mode register, then read the stable
   51  * value from the corresponding I/O port.  For example, you write
   52  * TMR_MR_LATCH into the corresponding mode register.  Presumably,
   53  * after doing this, a write operation to the I/O port would result
   54  * in undefined behavior (but hopefully not fry the chip).
   55  * Reading in this manner has no side effects.
   56  */
   57 
   58 /*
   59  * Macros for specifying values to be written into a mode register.
   60  */
   61 #define TIMER_REG_CNTR0 0       /* timer 0 counter port */
   62 #define TIMER_REG_CNTR1 1       /* timer 1 counter port */
   63 #define TIMER_REG_CNTR2 2       /* timer 2 counter port */
   64 #define TIMER_REG_MODE  3       /* timer mode port */
   65 #define         TIMER_SEL0      0x00    /* select counter 0 */
   66 #define         TIMER_SEL1      0x40    /* select counter 1 */
   67 #define         TIMER_SEL2      0x80    /* select counter 2 */
   68 #define         TIMER_INTTC     0x00    /* mode 0, intr on terminal cnt */
   69 #define         TIMER_ONESHOT   0x02    /* mode 1, one shot */
   70 #define         TIMER_RATEGEN   0x04    /* mode 2, rate generator */
   71 #define         TIMER_SQWAVE    0x06    /* mode 3, square wave */
   72 #define         TIMER_SWSTROBE  0x08    /* mode 4, s/w triggered strobe */
   73 #define         TIMER_HWSTROBE  0x0a    /* mode 5, h/w triggered strobe */
   74 #define         TIMER_LATCH     0x00    /* latch counter for reading */
   75 #define         TIMER_LSB       0x10    /* r/w counter LSB */
   76 #define         TIMER_MSB       0x20    /* r/w counter MSB */
   77 #define         TIMER_16BIT     0x30    /* r/w counter 16 bits, LSB first */
   78 #define         TIMER_BCD       0x01    /* count in BCD */

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