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/*
* Copyright (C) 2008 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 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., 675 Mass Ave, Cambridge, MA 02139, USA.
*/
FILE_LICENCE ( GPL2_OR_LATER );
/** @file
*
* RDTSC timer
*
*/
#include <assert.h>
#include <gpxe/timer.h>
#include <gpxe/timer2.h>
/**
* Number of TSC ticks per microsecond
*
* This is calibrated on the first use of the timer.
*/
static unsigned long rdtsc_ticks_per_usec;
/**
* Delay for a fixed number of microseconds
*
* @v usecs Number of microseconds for which to delay
*/
static void rdtsc_udelay ( unsigned long usecs ) {
unsigned long start;
unsigned long elapsed;
/* Sanity guard, since we may divide by this */
if ( ! usecs )
usecs = 1;
start = currticks();
if ( rdtsc_ticks_per_usec ) {
/* Already calibrated; busy-wait until done */
do {
elapsed = ( currticks() - start );
} while ( elapsed < ( usecs * rdtsc_ticks_per_usec ) );
} else {
/* Not yet calibrated; use timer2 and calibrate
* based on result.
*/
timer2_udelay ( usecs );
elapsed = ( currticks() - start );
rdtsc_ticks_per_usec = ( elapsed / usecs );
DBG ( "RDTSC timer calibrated: %ld ticks in %ld usecs "
"(%ld MHz)\n", elapsed, usecs,
( rdtsc_ticks_per_usec << TSC_SHIFT ) );
}
}
/**
* Get number of ticks per second
*
* @ret ticks_per_sec Number of ticks per second
*/
static unsigned long rdtsc_ticks_per_sec ( void ) {
/* Calibrate timer, if not already done */
if ( ! rdtsc_ticks_per_usec )
udelay ( 1 );
/* Sanity check */
assert ( rdtsc_ticks_per_usec != 0 );
return ( rdtsc_ticks_per_usec * 1000 * 1000 );
}
PROVIDE_TIMER ( rdtsc, udelay, rdtsc_udelay );
PROVIDE_TIMER_INLINE ( rdtsc, currticks );
PROVIDE_TIMER ( rdtsc, ticks_per_sec, rdtsc_ticks_per_sec );
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