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[timer] Rewrite the 8254 Programmable Interval Timer support
The 8254 timer code (used to implement udelay()) has an unknown provenance. Rewrite this code to avoid potential licensing uncertainty. Signed-off-by: Michael Brown <mcb30@ipxe.org>
This commit is contained in:
Michael Brown
66
src/arch/x86/core/pit8254.c
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66
src/arch/x86/core/pit8254.c
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/*
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* Copyright (C) 2015 Michael Brown <mbrown@fensystems.co.uk>.
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License as
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* published by the Free Software Foundation; either version 2 of the
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* License, or (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful, but
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* WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
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* 02110-1301, USA.
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*/
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FILE_LICENCE ( GPL2_OR_LATER );
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#include <assert.h>
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#include <ipxe/io.h>
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#include <ipxe/pit8254.h>
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/** @file
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*
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* 8254 Programmable Interval Timer
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*
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*/
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/**
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* Delay for a fixed number of timer ticks using the speaker channel
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*
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* @v ticks Number of timer ticks for which to delay
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*/
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void pit8254_speaker_delay ( unsigned int ticks ) {
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uint8_t spkr;
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uint8_t cmd;
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uint8_t low;
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uint8_t high;
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/* Sanity check */
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assert ( ticks <= 0xffff );
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/* Disable speaker, set speaker channel gate input high */
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spkr = inb ( PIT8254_SPKR );
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spkr &= ~PIT8254_SPKR_ENABLE;
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spkr |= PIT8254_SPKR_GATE;
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outb ( spkr, PIT8254_SPKR );
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/* Program speaker channel to "interrupt" on terminal count */
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cmd = ( PIT8254_CMD_CHANNEL ( PIT8254_CH_SPKR ) |
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PIT8254_CMD_ACCESS_LOHI | PIT8254_CMD_OP_TERMINAL |
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PIT8254_CMD_BINARY );
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low = ( ( ticks >> 0 ) & 0xff );
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high = ( ( ticks >> 8 ) & 0xff );
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outb ( cmd, PIT8254_CMD );
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outb ( low, PIT8254_DATA ( PIT8254_CH_SPKR ) );
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outb ( high, PIT8254_DATA ( PIT8254_CH_SPKR ) );
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/* Wait for channel to "interrupt" */
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do {
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spkr = inb ( PIT8254_SPKR );
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} while ( ! ( spkr & PIT8254_SPKR_OUT ) );
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}
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81
src/arch/x86/include/ipxe/pit8254.h
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81
src/arch/x86/include/ipxe/pit8254.h
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#ifndef _IPXE_PIT8254_H
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#define _IPXE_PIT8254_H
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/** @file
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*
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* 8254 Programmable Interval Timer
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*
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*/
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FILE_LICENCE ( GPL2_OR_LATER );
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/** IRQ0 channel */
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#define PIT8254_CH_IRQ0 0
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/** PC speaker channel */
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#define PIT8254_CH_SPKR 2
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/** Timer frequency (1.193182MHz) */
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#define PIT8254_HZ 1193182UL
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/** Data port */
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#define PIT8254_DATA(channel) ( 0x40 + (channel) )
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/** Mode/command register */
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#define PIT8254_CMD 0x43
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/** Select channel */
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#define PIT8254_CMD_CHANNEL(channel) ( (channel) << 6 )
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/** Access modes */
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#define PIT8254_CMD_ACCESS_LATCH 0x00 /**< Latch count value command */
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#define PIT8254_CMD_ACCESS_LO 0x10 /**< Low byte only */
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#define PIT8254_CMD_ACCESS_HI 0x20 /**< High byte only */
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#define PIT8254_CMD_ACCESS_LOHI 0x30 /**< Low-byte, high-byte pair */
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/* Operating modes */
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#define PIT8254_CMD_OP_TERMINAL 0x00 /**< Interrupt on terminal count */
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#define PIT8254_CMD_OP_ONESHOT 0x02 /**< Hardware re-triggerable one-shot */
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#define PIT8254_CMD_OP_RATE 0x04 /**< Rate generator */
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#define PIT8254_CMD_OP_SQUARE 0x06 /**< Square wave generator */
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#define PIT8254_CMD_OP_SWSTROBE 0x08 /**< Software triggered strobe */
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#define PIT8254_CMD_OP_HWSTROBE 0x0a /**< Hardware triggered strobe */
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#define PIT8254_CMD_OP_RATE2 0x0c /**< Rate generator (duplicate) */
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#define PIT8254_CMD_OP_SQUARE2 0x0e /**< Square wave generator (duplicate)*/
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/** Binary mode */
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#define PIT8254_CMD_BINARY 0x00
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/** BCD mode */
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#define PIT8254_CMD_BCD 0x01
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/** PC speaker control register */
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#define PIT8254_SPKR 0x61
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/** PC speaker channel gate */
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#define PIT8254_SPKR_GATE 0x01
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/** PC speaker enabled */
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#define PIT8254_SPKR_ENABLE 0x02
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/** PC speaker channel output */
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#define PIT8254_SPKR_OUT 0x20
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extern void pit8254_speaker_delay ( unsigned int ticks );
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/**
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* Delay for a fixed number of microseconds
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*
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* @v usecs Number of microseconds for which to delay
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*/
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static inline __attribute__ (( always_inline )) void
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pit8254_udelay ( unsigned long usecs ) {
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/* Delays are invariably compile-time constants; force the
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* multiplication and division to take place at compilation
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* time rather than runtime.
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*/
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pit8254_speaker_delay ( ( usecs * PIT8254_HZ ) / 1000000 );
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}
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#endif /* _IPXE_PIT8254_H */
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