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Annotation of Net2/arch/i386/isa/timerreg.h, revision 1.1

1.1     ! root        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:  * 3. All advertising materials mentioning features or use of this software
        !            14:  *    must display the following acknowledgement:
        !            15:  *      This product includes software developed by the University of
        !            16:  *      California, Berkeley and its contributors.
        !            17:  * 4. Neither the name of the University nor the names of its contributors
        !            18:  *    may be used to endorse or promote products derived from this software
        !            19:  *    without specific prior written permission.
        !            20:  *
        !            21:  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
        !            22:  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
        !            23:  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
        !            24:  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
        !            25:  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
        !            26:  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
        !            27:  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
        !            28:  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
        !            29:  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
        !            30:  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
        !            31:  * SUCH DAMAGE.
        !            32:  *
        !            33:  * $Header: /cvsroot/src/sys/arch/i386/isa/Attic/timerreg.h,v 1.1 1993/03/23 08:12:25 cgd Exp $
        !            34:  *
        !            35:  * Register definitions for the Intel 8253 Programmable Interval Timer.
        !            36:  *
        !            37:  * This chip has three independent 16-bit down counters that can be
        !            38:  * read on the fly.  There are three mode registers and three countdown
        !            39:  * registers.  The countdown registers are addressed directly, via the
        !            40:  * first three I/O ports.  The three mode registers are accessed via
        !            41:  * the fourth I/O port, with two bits in the mode byte indicating the
        !            42:  * register.  (Why are hardware interfaces always so braindead?).
        !            43:  *
        !            44:  * To write a value into the countdown register, the mode register
        !            45:  * is first programmed with a command indicating the which byte of
        !            46:  * the two byte register is to be modified.  The three possibilities
        !            47:  * are load msb (TMR_MR_MSB), load lsb (TMR_MR_LSB), or load lsb then
        !            48:  * msb (TMR_MR_BOTH).
        !            49:  *
        !            50:  * To read the current value ("on the fly") from the countdown register,
        !            51:  * you write a "latch" command into the mode register, then read the stable
        !            52:  * value from the corresponding I/O port.  For example, you write
        !            53:  * TMR_MR_LATCH into the corresponding mode register.  Presumably,
        !            54:  * after doing this, a write operation to the I/O port would result
        !            55:  * in undefined behavior (but hopefully not fry the chip).
        !            56:  * Reading in this manner has no side effects.
        !            57:  *
        !            58:  * The outputs of the three timers are connected as follows:
        !            59:  *
        !            60:  *      timer 0 -> irq 0
        !            61:  *      timer 1 -> dma chan 0 (for dram refresh)
        !            62:  *      timer 2 -> speaker (via keyboard controller)
        !            63:  *
        !            64:  * Timer 0 is used to call hardclock.
        !            65:  * Timer 2 is used to generate console beeps.
        !            66:  */
        !            67: 
        !            68: /*
        !            69:  * Macros for specifying values to be written into a mode register.
        !            70:  */
        !            71: #define        TIMER_CNTR0     (IO_TIMER1 + 0) /* timer 0 counter port */
        !            72: #define        TIMER_CNTR1     (IO_TIMER1 + 1) /* timer 1 counter port */
        !            73: #define        TIMER_CNTR2     (IO_TIMER1 + 2) /* timer 2 counter port */
        !            74: #define        TIMER_MODE      (IO_TIMER1 + 3) /* timer mode port */
        !            75: #define                TIMER_SEL0      0x00    /* select counter 0 */
        !            76: #define                TIMER_SEL1      0x40    /* select counter 1 */
        !            77: #define                TIMER_SEL2      0x80    /* select counter 2 */
        !            78: #define                TIMER_INTTC     0x00    /* mode 0, intr on terminal cnt */
        !            79: #define                TIMER_ONESHOT   0x02    /* mode 1, one shot */
        !            80: #define                TIMER_RATEGEN   0x04    /* mode 2, rate generator */
        !            81: #define                TIMER_SQWAVE    0x06    /* mode 3, square wave */
        !            82: #define                TIMER_SWSTROBE  0x08    /* mode 4, s/w triggered strobe */
        !            83: #define                TIMER_HWSTROBE  0x0a    /* mode 5, h/w triggered strobe */
        !            84: #define                TIMER_LATCH     0x00    /* latch counter for reading */
        !            85: #define                TIMER_LSB       0x10    /* r/w counter LSB */
        !            86: #define                TIMER_MSB       0x20    /* r/w counter MSB */
        !            87: #define                TIMER_16BIT     0x30    /* r/w counter 16 bits, LSB first */
        !            88: #define                TIMER_BCD       0x01    /* count in BCD */
        !            89: 

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