src/arch/i386/core/rdtsc_timer.c

   1 /*
   2  * Copyright (C) 2008 Michael Brown <mbrown@fensystems.co.uk>.
   3  *
   4  * This program is free software; you can redistribute it and/or
   5  * modify it under the terms of the GNU General Public License as
   6  * published by the Free Software Foundation; either version 2 of the
   7  * License, or any later version.
   8  *
   9  * This program is distributed in the hope that it will be useful, but
  10  * WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12  * General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU General Public License
  15  * along with this program; if not, write to the Free Software
  16  * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  17  */
  18
  19 FILE_LICENCE ( GPL2_OR_LATER );
  20
  21 /** @file
  22  *
  23  * RDTSC timer
  24  *
  25  */
  26
  27 #include <assert.h>
  28 #include <gpxe/timer.h>
  29 #include <gpxe/timer2.h>
  30
  31 /**
  32  * Number of TSC ticks per microsecond
  33  *
  34  * This is calibrated on the first use of the timer.
  35  */
  36 static unsigned long rdtsc_ticks_per_usec;
  37
  38 /**
  39  * Delay for a fixed number of microseconds
  40  *
  41  * @v usecs             Number of microseconds for which to delay
  42  */
  43 static void rdtsc_udelay ( unsigned long usecs ) {
  44         unsigned long start;
  45         unsigned long elapsed;
  46
  47         /* Sanity guard, since we may divide by this */
  48         if ( ! usecs )
  49                 usecs = 1;
  50
  51         start = currticks();
  52         if ( rdtsc_ticks_per_usec ) {
  53                 /* Already calibrated; busy-wait until done */
  54                 do {
  55                         elapsed = ( currticks() - start );
  56                 } while ( elapsed < ( usecs * rdtsc_ticks_per_usec ) );
  57         } else {
  58                 /* Not yet calibrated; use timer2 and calibrate
  59                  * based on result.
  60                  */
  61                 timer2_udelay ( usecs );
  62                 elapsed = ( currticks() - start );
  63                 rdtsc_ticks_per_usec = ( elapsed / usecs );
  64                 DBG ( "RDTSC timer calibrated: %ld ticks in %ld usecs "
  65                       "(%ld MHz)\n", elapsed, usecs,
  66                       ( rdtsc_ticks_per_usec << TSC_SHIFT ) );
  67         }
  68 }
  69
  70 /**
  71  * Get number of ticks per second
  72  *
  73  * @ret ticks_per_sec   Number of ticks per second
  74  */
  75 static unsigned long rdtsc_ticks_per_sec ( void ) {
  76
  77         /* Calibrate timer, if not already done */
  78         if ( ! rdtsc_ticks_per_usec )
  79                 udelay ( 1 );
  80
  81         /* Sanity check */
  82         assert ( rdtsc_ticks_per_usec != 0 );
  83
  84         return ( rdtsc_ticks_per_usec * 1000 * 1000 );
  85 }
  86
  87 PROVIDE_TIMER ( rdtsc, udelay, rdtsc_udelay );
  88 PROVIDE_TIMER_INLINE ( rdtsc, currticks );
  89 PROVIDE_TIMER ( rdtsc, ticks_per_sec, rdtsc_ticks_per_sec );