freebsd-dev/sys/amd64/include/clock.h
Garrett Wollman e2d4b1f051 Reduce jitter of Pentium microtime() implementation by letting the counter
free-run and doing a subtract in microtime() rather than resetting the
counter to zero at every clock tick.  In combination with the changes to
kern_clock.c, this should eliminate all the immediately obvious sources
of systematic jitter in timekeeping on Pentium machines.
1995-10-12 20:39:49 +00:00

100 lines
2.3 KiB
C

/*
* Kernel interface to machine-dependent clock driver.
* Garrett Wollman, September 1994.
* This file is in the public domain.
*/
#ifndef _MACHINE_CLOCK_H_
#define _MACHINE_CLOCK_H_
#ifdef I586_CPU
#define I586_CYCLECTR(x) \
__asm __volatile(".byte 0x0f, 0x31" : "=A" (x))
/*
* When we update the clock, we also update this bias value which is
* automatically subtracted in microtime(). We assume that CPU_THISTICKLEN()
* has been called at some point in the past, so that an appropriate value is
* set up in i586_last_tick. (This works even if we are not being called
* from hardclock because hardclock will have run before and will made the
* call.)
*/
#define CPU_CLOCKUPDATE(otime, ntime) \
do { \
if(pentium_mhz) { \
disable_intr(); \
i586_ctr_bias = i586_last_tick; \
*(otime) = *(ntime); \
enable_intr(); \
} else { \
*(otime) = *(ntime); \
} \
} while(0)
#define CPU_THISTICKLEN(dflt) cpu_thisticklen(dflt)
#else
#define CPU_CLOCKUPDATE(otime, ntime) \
(*(otime) = *(ntime))
#define CPU_THISTICKLEN(dflt) dflt
#endif
#if defined(KERNEL) && !defined(LOCORE)
#include <sys/cdefs.h>
#include <machine/frame.h>
/*
* i386 to clock driver interface.
* XXX almost all of it is misplaced. i586 stuff is done in isa/clock.c
* and isa stuff is done in i386/microtime.s and i386/support.s.
*/
extern int adjkerntz;
extern int disable_rtc_set;
#ifdef I586_CPU
extern int pentium_mhz;
extern long long i586_last_tick;
extern long long i586_ctr_bias;
#endif
extern int timer0_max_count;
extern u_int timer0_overflow_threshold;
extern u_int timer0_prescaler_count;
#ifdef I586_CPU
void calibrate_cyclecounter __P((void));
#endif
void clkintr __P((struct clockframe frame));
void rtcintr __P((struct clockframe frame));
#ifdef I586_CPU
static __inline u_long
cpu_thisticklen(u_long dflt)
{
long long old;
long rv;
if (pentium_mhz) {
old = i586_last_tick;
I586_CYCLECTR(i586_last_tick);
rv = (i586_last_tick - old) / pentium_mhz;
} else {
rv = dflt;
}
return rv;
}
#endif
/*
* Driver to clock driver interface.
*/
void DELAY __P((int usec));
int acquire_timer0 __P((int rate,
void (*function)(struct clockframe *frame)));
int acquire_timer2 __P((int mode));
int release_timer0 __P((void));
int release_timer2 __P((void));
int sysbeep __P((int pitch, int period));
#endif /* KERNEL && !LOCORE */
#endif /* !_MACHINE_CLOCK_H_ */