2 * Copyright (C) 2008 Michael Brown <mbrown@fensystems.co.uk>.
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.
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.
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., 51 Franklin Street, Fifth Floor, Boston, MA
20 FILE_LICENCE ( GPL2_OR_LATER );
29 #include <ipxe/timer.h>
30 #include <ipxe/timer2.h>
33 * Number of TSC ticks per microsecond
35 * This is calibrated on the first use of the timer.
37 static unsigned long rdtsc_ticks_per_usec;
40 * Delay for a fixed number of microseconds
42 * @v usecs Number of microseconds for which to delay
44 static void rdtsc_udelay ( unsigned long usecs ) {
46 unsigned long elapsed;
48 /* Sanity guard, since we may divide by this */
53 if ( rdtsc_ticks_per_usec ) {
54 /* Already calibrated; busy-wait until done */
56 elapsed = ( currticks() - start );
57 } while ( elapsed < ( usecs * rdtsc_ticks_per_usec ) );
59 /* Not yet calibrated; use timer2 and calibrate
62 timer2_udelay ( usecs );
63 elapsed = ( currticks() - start );
64 rdtsc_ticks_per_usec = ( elapsed / usecs );
65 DBG ( "RDTSC timer calibrated: %ld ticks in %ld usecs "
66 "(%ld MHz)\n", elapsed, usecs,
67 ( rdtsc_ticks_per_usec << TSC_SHIFT ) );
72 * Get number of ticks per second
74 * @ret ticks_per_sec Number of ticks per second
76 static unsigned long rdtsc_ticks_per_sec ( void ) {
78 /* Calibrate timer, if not already done */
79 if ( ! rdtsc_ticks_per_usec )
83 assert ( rdtsc_ticks_per_usec != 0 );
85 return ( rdtsc_ticks_per_usec * 1000 * 1000 );
88 PROVIDE_TIMER ( rdtsc, udelay, rdtsc_udelay );
89 PROVIDE_TIMER_INLINE ( rdtsc, currticks );
90 PROVIDE_TIMER ( rdtsc, ticks_per_sec, rdtsc_ticks_per_sec );