FreeBSD/Linux Kernel Cross Reference
sys/dev/ic/i8253reg.h
1 /* $OpenBSD: i8253reg.h,v 1.3 2003/06/02 23:28:02 millert Exp $ */
2 /* $NetBSD: i8253reg.h,v 1.5 1998/01/19 11:38:00 drochner Exp $ */
3
4 /*-
5 * Copyright (c) 1993 The Regents of the University of California.
6 * All rights reserved.
7 *
8 * Redistribution and use in source and binary forms, with or without
9 * modification, are permitted provided that the following conditions
10 * are met:
11 * 1. Redistributions of source code must retain the above copyright
12 * notice, this list of conditions and the following disclaimer.
13 * 2. Redistributions in binary form must reproduce the above copyright
14 * notice, this list of conditions and the following disclaimer in the
15 * documentation and/or other materials provided with the distribution.
16 * 3. Neither the name of the University nor the names of its contributors
17 * may be used to endorse or promote products derived from this software
18 * without specific prior written permission.
19 *
20 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
21 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
22 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
23 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
24 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
25 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
26 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
27 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
28 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
29 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
30 * SUCH DAMAGE.
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 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 * The outputs of the three timers are connected as follows:
58 *
59 * timer 0 -> irq 0
60 * timer 1 -> dma chan 0 (for dram refresh)
61 * timer 2 -> speaker (via keyboard controller)
62 *
63 * Timer 0 is used to call hardclock.
64 * Timer 2 is used to generate console beeps.
65 */
66
67 /*
68 * Frequency of all three count-down timers; (TIMER_FREQ/freq) is the
69 * appropriate count to generate a frequency of freq hz.
70 */
71 #ifndef TIMER_FREQ
72 #define TIMER_FREQ 1193182
73 #endif
74 #define TIMER_DIV(x) ((TIMER_FREQ+(x)/2)/(x))
75
76 /*
77 * Macros for specifying values to be written into a mode register.
78 */
79 #define TIMER_CNTR0 0 /* timer 0 counter port */
80 #define TIMER_CNTR1 1 /* timer 1 counter port */
81 #define TIMER_CNTR2 2 /* timer 2 counter port */
82 #define TIMER_MODE 3 /* timer mode port */
83 #define TIMER_SEL0 0x00 /* select counter 0 */
84 #define TIMER_SEL1 0x40 /* select counter 1 */
85 #define TIMER_SEL2 0x80 /* select counter 2 */
86 #define TIMER_INTTC 0x00 /* mode 0, intr on terminal cnt */
87 #define TIMER_ONESHOT 0x02 /* mode 1, one shot */
88 #define TIMER_RATEGEN 0x04 /* mode 2, rate generator */
89 #define TIMER_SQWAVE 0x06 /* mode 3, square wave */
90 #define TIMER_SWSTROBE 0x08 /* mode 4, s/w triggered strobe */
91 #define TIMER_HWSTROBE 0x0a /* mode 5, h/w triggered strobe */
92 #define TIMER_LATCH 0x00 /* latch counter for reading */
93 #define TIMER_LSB 0x10 /* r/w counter LSB */
94 #define TIMER_MSB 0x20 /* r/w counter MSB */
95 #define TIMER_16BIT 0x30 /* r/w counter 16 bits, LSB first */
96 #define TIMER_BCD 0x01 /* count in BCD */
97
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