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[timer] Rewrite the 8254 Programmable Interval Timer support

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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
2015-02-17 16:24:02 +00:00
parent 320e786d3d
commit 08189df4e0
6 changed files with 153 additions and 107 deletions
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66
src/arch/x86/core/pit8254.c Normal file
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/*
* Copyright (C) 2015 Michael Brown <mbrown@fensystems.co.uk>.
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License as
* published by the Free Software Foundation; either version 2 of the
* License, or (at your option) any later version.
*
* This program is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
* 02110-1301, USA.
*/
FILE_LICENCE ( GPL2_OR_LATER );
#include <assert.h>
#include <ipxe/io.h>
#include <ipxe/pit8254.h>
/** @file
*
* 8254 Programmable Interval Timer
*
*/
/**
* Delay for a fixed number of timer ticks using the speaker channel
*
* @v ticks Number of timer ticks for which to delay
*/
void pit8254_speaker_delay ( unsigned int ticks ) {
uint8_t spkr;
uint8_t cmd;
uint8_t low;
uint8_t high;
/* Sanity check */
assert ( ticks <= 0xffff );
/* Disable speaker, set speaker channel gate input high */
spkr = inb ( PIT8254_SPKR );
spkr &= ~PIT8254_SPKR_ENABLE;
spkr |= PIT8254_SPKR_GATE;
outb ( spkr, PIT8254_SPKR );
/* Program speaker channel to "interrupt" on terminal count */
cmd = ( PIT8254_CMD_CHANNEL ( PIT8254_CH_SPKR ) |
PIT8254_CMD_ACCESS_LOHI | PIT8254_CMD_OP_TERMINAL |
PIT8254_CMD_BINARY );
low = ( ( ticks >> 0 ) & 0xff );
high = ( ( ticks >> 8 ) & 0xff );
outb ( cmd, PIT8254_CMD );
outb ( low, PIT8254_DATA ( PIT8254_CH_SPKR ) );
outb ( high, PIT8254_DATA ( PIT8254_CH_SPKR ) );
/* Wait for channel to "interrupt" */
do {
spkr = inb ( PIT8254_SPKR );
} while ( ! ( spkr & PIT8254_SPKR_OUT ) );
}