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Diffstat (limited to 'sys/isa/timerreg.h')
| -rw-r--r-- | sys/isa/timerreg.h | 89 |
1 files changed, 89 insertions, 0 deletions
diff --git a/sys/isa/timerreg.h b/sys/isa/timerreg.h new file mode 100644 index 0000000..72c7022 --- /dev/null +++ b/sys/isa/timerreg.h @@ -0,0 +1,89 @@ +/*- + * 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. All advertising materials mentioning features or use of this software + * must display the following acknowledgement: + * This product includes software developed by the University of + * California, Berkeley and its contributors. + * 4. 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. + * + * $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. + * + * The outputs of the three timers are connected as follows: + * + * timer 0 -> irq 0 + * timer 1 -> dma chan 0 (for dram refresh) + * timer 2 -> speaker (via keyboard controller) + * + * Timer 0 is used to call hardclock. + * Timer 2 is used to generate console beeps. + */ + +/* + * Macros for specifying values to be written into a mode register. + */ +#define TIMER_CNTR0 (IO_TIMER1 + 0) /* timer 0 counter port */ +#define TIMER_CNTR1 (IO_TIMER1 + 1) /* timer 1 counter port */ +#define TIMER_CNTR2 (IO_TIMER1 + 2) /* timer 2 counter port */ +#define TIMER_MODE (IO_TIMER1 + 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 */ + |
