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[PATCH] ntp: prescale time_offset 

This converts time_offset into a scaled per tick value.  This avoids now
completely the crude compensation in second_overflow().

Signed-off-by: Roman Zippel <zippel@linux-m68k.org>
Cc: john stultz <johnstul@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Roman Zippel 2006-09-30 23:28:25 -07:00 committed by Linus Torvalds
parent dc6a43e46f
commit 3d3675cc3d
2 changed files with 17 additions and 49 deletions
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2
include/linux/timex.h
View File

@ -89,7 +89,7 @@
* FINENSEC is 1 ns in SHIFT_UPDATE units of the time_phase variable.
*/
#define SHIFT_SCALE 22 /* phase scale (shift) */
#define SHIFT_UPDATE (SHIFT_KG + MAXTC) /* time offset scale (shift) */
#define SHIFT_UPDATE (SHIFT_HZ + 1) /* time offset scale (shift) */
#define SHIFT_USEC 16 /* frequency offset scale (shift) */
#define FINENSEC (1L << (SHIFT_SCALE - 10)) /* ~1 ns in phase units */

64
kernel/time/ntp.c
View File

@ -31,7 +31,7 @@ int tickadj = 500/HZ ? : 1; /* microsecs */
/* TIME_ERROR prevents overwriting the CMOS clock */
int time_state = TIME_OK; /* clock synchronization status */
int time_status = STA_UNSYNC; /* clock status bits */
long time_offset; /* time adjustment (us) */
long time_offset; /* time adjustment (ns) */
long time_constant = 2; /* pll time constant */
long time_tolerance = MAXFREQ; /* frequency tolerance (ppm) */
long time_precision = 1; /* clock precision (us) */
@ -57,6 +57,7 @@ void ntp_clear(void)
ntp_update_frequency();
tick_length = tick_length_base;
time_offset = 0;
}
#define CLOCK_TICK_OVERFLOW (LATCH * HZ - CLOCK_TICK_RATE)
@ -83,7 +84,7 @@ void ntp_update_frequency(void)
*/
void second_overflow(void)
{
long ltemp, time_adj;
long time_adj;
/* Bump the maxerror field */
time_maxerror += time_tolerance >> SHIFT_USEC;
@ -151,42 +152,14 @@ void second_overflow(void)
* adjustment for each second is clamped so as to spread the adjustment
* over not more than the number of seconds between updates.
*/
ltemp = time_offset;
if (!(time_status & STA_FLL))
ltemp = shift_right(ltemp, SHIFT_KG + time_constant);
ltemp = min(ltemp, (MAXPHASE / MINSEC) << SHIFT_UPDATE);
ltemp = max(ltemp, -(MAXPHASE / MINSEC) << SHIFT_UPDATE);
time_offset -= ltemp;
time_adj = ltemp << (SHIFT_SCALE - SHIFT_HZ - SHIFT_UPDATE);
/*
* Compute the frequency estimate and additional phase adjustment due
* to frequency error for the next second.
*/
#if HZ == 100
/*
* Compensate for (HZ==100) != (1 << SHIFT_HZ). Add 25% and 3.125% to
* get 128.125; => only 0.125% error (p. 14)
*/
time_adj += shift_right(time_adj, 2) + shift_right(time_adj, 5);
#endif
#if HZ == 250
/*
* Compensate for (HZ==250) != (1 << SHIFT_HZ). Add 1.5625% and
* 0.78125% to get 255.85938; => only 0.05% error (p. 14)
*/
time_adj += shift_right(time_adj, 6) + shift_right(time_adj, 7);
#endif
#if HZ == 1000
/*
* Compensate for (HZ==1000) != (1 << SHIFT_HZ). Add 1.5625% and
* 0.78125% to get 1023.4375; => only 0.05% error (p. 14)
*/
time_adj += shift_right(time_adj, 6) + shift_right(time_adj, 7);
#endif
tick_length = tick_length_base;
tick_length += (s64)time_adj << (TICK_LENGTH_SHIFT - (SHIFT_SCALE - 10));
time_adj = time_offset;
if (!(time_status & STA_FLL))
time_adj = shift_right(time_adj, SHIFT_KG + time_constant);
time_adj = min(time_adj, -((MAXPHASE / HZ) << SHIFT_UPDATE) / MINSEC);
time_adj = max(time_adj, ((MAXPHASE / HZ) << SHIFT_UPDATE) / MINSEC);
time_offset -= time_adj;
tick_length += (s64)time_adj << (TICK_LENGTH_SHIFT - SHIFT_UPDATE);
}
/*
@ -347,12 +320,8 @@ int do_adjtimex(struct timex *txc)
* Scale the phase adjustment and
* clamp to the operating range.
*/
if (ltemp > MAXPHASE)
time_offset = MAXPHASE << SHIFT_UPDATE;
else if (ltemp < -MAXPHASE)
time_offset = -(MAXPHASE << SHIFT_UPDATE);
else
time_offset = ltemp << SHIFT_UPDATE;
time_offset = min(ltemp, MAXPHASE);
time_offset = max(time_offset, -MAXPHASE);
/*
* Select whether the frequency is to be controlled
@ -366,8 +335,7 @@ int do_adjtimex(struct timex *txc)
time_reftime = xtime.tv_sec;
if (time_status & STA_FLL) {
if (mtemp >= MINSEC) {
ltemp = (time_offset / mtemp) << (SHIFT_USEC -
SHIFT_UPDATE);
ltemp = ((time_offset << 12) / mtemp) << (SHIFT_USEC - 12);
time_freq += shift_right(ltemp, SHIFT_KH);
} else /* calibration interval too short (p. 12) */
result = TIME_ERROR;
@ -382,6 +350,7 @@ int do_adjtimex(struct timex *txc)
}
time_freq = min(time_freq, time_tolerance);
time_freq = max(time_freq, -time_tolerance);
time_offset = (time_offset * NSEC_PER_USEC / HZ) << SHIFT_UPDATE;
} /* STA_PLL */
} /* txc->modes & ADJ_OFFSET */
if (txc->modes & ADJ_TICK)
@ -395,9 +364,8 @@ leave: if ((time_status & (STA_UNSYNC|STA_CLOCKERR)) != 0)
if ((txc->modes & ADJ_OFFSET_SINGLESHOT) == ADJ_OFFSET_SINGLESHOT)
txc->offset = save_adjust;
else {
txc->offset = shift_right(time_offset, SHIFT_UPDATE);
}
else
txc->offset = shift_right(time_offset, SHIFT_UPDATE) * HZ / 1000;
txc->freq = time_freq;
txc->maxerror = time_maxerror;
txc->esterror = time_esterror;