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e2d4b1f051
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.
100 lines
2.3 KiB
C
100 lines
2.3 KiB
C
/*
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* Kernel interface to machine-dependent clock driver.
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* Garrett Wollman, September 1994.
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* This file is in the public domain.
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*/
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#ifndef _MACHINE_CLOCK_H_
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#define _MACHINE_CLOCK_H_
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#ifdef I586_CPU
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#define I586_CYCLECTR(x) \
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__asm __volatile(".byte 0x0f, 0x31" : "=A" (x))
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/*
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* When we update the clock, we also update this bias value which is
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* automatically subtracted in microtime(). We assume that CPU_THISTICKLEN()
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* has been called at some point in the past, so that an appropriate value is
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* set up in i586_last_tick. (This works even if we are not being called
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* from hardclock because hardclock will have run before and will made the
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* call.)
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*/
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#define CPU_CLOCKUPDATE(otime, ntime) \
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do { \
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if(pentium_mhz) { \
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disable_intr(); \
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i586_ctr_bias = i586_last_tick; \
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*(otime) = *(ntime); \
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enable_intr(); \
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} else { \
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*(otime) = *(ntime); \
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} \
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} while(0)
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#define CPU_THISTICKLEN(dflt) cpu_thisticklen(dflt)
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#else
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#define CPU_CLOCKUPDATE(otime, ntime) \
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(*(otime) = *(ntime))
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#define CPU_THISTICKLEN(dflt) dflt
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#endif
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#if defined(KERNEL) && !defined(LOCORE)
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#include <sys/cdefs.h>
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#include <machine/frame.h>
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/*
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* i386 to clock driver interface.
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* XXX almost all of it is misplaced. i586 stuff is done in isa/clock.c
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* and isa stuff is done in i386/microtime.s and i386/support.s.
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*/
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extern int adjkerntz;
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extern int disable_rtc_set;
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#ifdef I586_CPU
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extern int pentium_mhz;
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extern long long i586_last_tick;
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extern long long i586_ctr_bias;
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#endif
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extern int timer0_max_count;
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extern u_int timer0_overflow_threshold;
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extern u_int timer0_prescaler_count;
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#ifdef I586_CPU
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void calibrate_cyclecounter __P((void));
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#endif
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void clkintr __P((struct clockframe frame));
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void rtcintr __P((struct clockframe frame));
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#ifdef I586_CPU
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static __inline u_long
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cpu_thisticklen(u_long dflt)
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{
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long long old;
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long rv;
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if (pentium_mhz) {
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old = i586_last_tick;
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I586_CYCLECTR(i586_last_tick);
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rv = (i586_last_tick - old) / pentium_mhz;
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} else {
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rv = dflt;
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}
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return rv;
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}
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#endif
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/*
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* Driver to clock driver interface.
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*/
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void DELAY __P((int usec));
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int acquire_timer0 __P((int rate,
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void (*function)(struct clockframe *frame)));
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int acquire_timer2 __P((int mode));
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int release_timer0 __P((void));
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int release_timer2 __P((void));
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int sysbeep __P((int pitch, int period));
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#endif /* KERNEL && !LOCORE */
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#endif /* !_MACHINE_CLOCK_H_ */
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