rdtsc_timer.c

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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 );