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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 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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6
src/arch/i386/core/rdtsc_timer.c
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@ -27,7 +27,7 @@ FILE_LICENCE ( GPL2_OR_LATER );
#include <assert.h>
#include <ipxe/timer.h>
#include <ipxe/timer2.h>
#include <ipxe/pit8254.h>
/**
* Number of TSC ticks per microsecond
@ -56,10 +56,10 @@ static void rdtsc_udelay ( unsigned long usecs ) {
elapsed = ( currticks() - start );
} while ( elapsed < ( usecs * rdtsc_ticks_per_usec ) );
} else {
/* Not yet calibrated; use timer2 and calibrate
/* Not yet calibrated; use 8254 PIT and calibrate
* based on result.
*/
timer2_udelay ( usecs );
pit8254_udelay ( usecs );
elapsed = ( currticks() - start );
rdtsc_ticks_per_usec = ( elapsed / usecs );
DBG ( "RDTSC timer calibrated: %ld ticks in %ld usecs "

87
src/arch/i386/core/timer2.c
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@ -1,87 +0,0 @@
/*
* arch/i386/core/i386_timer.c
*
* Use the "System Timer 2" to implement the udelay callback in
* the BIOS timer driver. Also used to calibrate the clock rate
* in the RTDSC timer driver.
*
* 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, or (at
* your option) any later version.
*/
FILE_LICENCE ( GPL2_OR_LATER );
#include <stddef.h>
#include <ipxe/timer2.h>
#include <ipxe/io.h>
/* Timers tick over at this rate */
#define TIMER2_TICKS_PER_SEC 1193180U
/* Parallel Peripheral Controller Port B */
#define PPC_PORTB 0x61
/* Meaning of the port bits */
#define PPCB_T2OUT 0x20 /* Bit 5 */
#define PPCB_SPKR 0x02 /* Bit 1 */
#define PPCB_T2GATE 0x01 /* Bit 0 */
/* Ports for the 8254 timer chip */
#define TIMER2_PORT 0x42
#define TIMER_MODE_PORT 0x43
/* Meaning of the mode bits */
#define TIMER0_SEL 0x00
#define TIMER1_SEL 0x40
#define TIMER2_SEL 0x80
#define READBACK_SEL 0xC0
#define LATCH_COUNT 0x00
#define LOBYTE_ACCESS 0x10
#define HIBYTE_ACCESS 0x20
#define WORD_ACCESS 0x30
#define MODE0 0x00
#define MODE1 0x02
#define MODE2 0x04
#define MODE3 0x06
#define MODE4 0x08
#define MODE5 0x0A
#define BINARY_COUNT 0x00
#define BCD_COUNT 0x01
static void load_timer2 ( unsigned int ticks ) {
/*
* Now let's take care of PPC channel 2
*
* Set the Gate high, program PPC channel 2 for mode 0,
* (interrupt on terminal count mode), binary count,
* load 5 * LATCH count, (LSB and MSB) to begin countdown.
*
* Note some implementations have a bug where the high bits byte
* of channel 2 is ignored.
*/
/* Set up the timer gate, turn off the speaker */
/* Set the Gate high, disable speaker */
outb((inb(PPC_PORTB) & ~PPCB_SPKR) | PPCB_T2GATE, PPC_PORTB);
/* binary, mode 0, LSB/MSB, Ch 2 */
outb(TIMER2_SEL|WORD_ACCESS|MODE0|BINARY_COUNT, TIMER_MODE_PORT);
/* LSB of ticks */
outb(ticks & 0xFF, TIMER2_PORT);
/* MSB of ticks */
outb(ticks >> 8, TIMER2_PORT);
}
static int timer2_running ( void ) {
return ((inb(PPC_PORTB) & PPCB_T2OUT) == 0);
}
void timer2_udelay ( unsigned long usecs ) {
load_timer2 ( ( usecs * TIMER2_TICKS_PER_SEC ) / ( 1000 * 1000 ) );
while (timer2_running()) {
/* Do nothing */
}
}

6
src/arch/i386/include/ipxe/bios_timer.h
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@ -15,7 +15,7 @@ FILE_LICENCE ( GPL2_OR_LATER );
#define TIMER_PREFIX_pcbios __pcbios_
#endif
#include <ipxe/timer2.h>
#include <ipxe/pit8254.h>
/**
* Delay for a fixed number of microseconds
@ -25,9 +25,9 @@ FILE_LICENCE ( GPL2_OR_LATER );
static inline __always_inline void
TIMER_INLINE ( pcbios, udelay ) ( unsigned long usecs ) {
/* BIOS timer is not high-resolution enough for udelay(), so
* we use timer2
* we use the 8254 Programmable Interval Timer.
*/
timer2_udelay ( usecs );
pit8254_udelay ( usecs );
}
/**

14
src/arch/i386/include/ipxe/timer2.h
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@ -1,14 +0,0 @@
#ifndef _IPXE_TIMER2_H
#define _IPXE_TIMER2_H
/** @file
*
* Timer chip control
*
*/
FILE_LICENCE ( GPL2_OR_LATER );
extern void timer2_udelay ( unsigned long usecs );
#endif /* _IPXE_TIMER2_H */

66
src/arch/x86/core/pit8254.c Normal file
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@ -0,0 +1,66 @@
/*
* 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 ) );
}

81
src/arch/x86/include/ipxe/pit8254.h Normal file
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@ -0,0 +1,81 @@
#ifndef _IPXE_PIT8254_H
#define _IPXE_PIT8254_H
/** @file
*
* 8254 Programmable Interval Timer
*
*/
FILE_LICENCE ( GPL2_OR_LATER );
/** IRQ0 channel */
#define PIT8254_CH_IRQ0 0
/** PC speaker channel */
#define PIT8254_CH_SPKR 2
/** Timer frequency (1.193182MHz) */
#define PIT8254_HZ 1193182UL
/** Data port */
#define PIT8254_DATA(channel) ( 0x40 + (channel) )
/** Mode/command register */
#define PIT8254_CMD 0x43
/** Select channel */
#define PIT8254_CMD_CHANNEL(channel) ( (channel) << 6 )
/** Access modes */
#define PIT8254_CMD_ACCESS_LATCH 0x00 /**< Latch count value command */
#define PIT8254_CMD_ACCESS_LO 0x10 /**< Low byte only */
#define PIT8254_CMD_ACCESS_HI 0x20 /**< High byte only */
#define PIT8254_CMD_ACCESS_LOHI 0x30 /**< Low-byte, high-byte pair */
/* Operating modes */
#define PIT8254_CMD_OP_TERMINAL 0x00 /**< Interrupt on terminal count */
#define PIT8254_CMD_OP_ONESHOT 0x02 /**< Hardware re-triggerable one-shot */
#define PIT8254_CMD_OP_RATE 0x04 /**< Rate generator */
#define PIT8254_CMD_OP_SQUARE 0x06 /**< Square wave generator */
#define PIT8254_CMD_OP_SWSTROBE 0x08 /**< Software triggered strobe */
#define PIT8254_CMD_OP_HWSTROBE 0x0a /**< Hardware triggered strobe */
#define PIT8254_CMD_OP_RATE2 0x0c /**< Rate generator (duplicate) */
#define PIT8254_CMD_OP_SQUARE2 0x0e /**< Square wave generator (duplicate)*/
/** Binary mode */
#define PIT8254_CMD_BINARY 0x00
/** BCD mode */
#define PIT8254_CMD_BCD 0x01
/** PC speaker control register */
#define PIT8254_SPKR 0x61
/** PC speaker channel gate */
#define PIT8254_SPKR_GATE 0x01
/** PC speaker enabled */
#define PIT8254_SPKR_ENABLE 0x02
/** PC speaker channel output */
#define PIT8254_SPKR_OUT 0x20
extern void pit8254_speaker_delay ( unsigned int ticks );
/**
* Delay for a fixed number of microseconds
*
* @v usecs Number of microseconds for which to delay
*/
static inline __attribute__ (( always_inline )) void
pit8254_udelay ( unsigned long usecs ) {
/* Delays are invariably compile-time constants; force the
* multiplication and division to take place at compilation
* time rather than runtime.
*/
pit8254_speaker_delay ( ( usecs * PIT8254_HZ ) / 1000000 );
}
#endif /* _IPXE_PIT8254_H */