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Subject[NTP 4/9] 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>
---
include/linux/timex.h | 2 -
kernel/time/ntp.c | 64 ++++++++++++--------------------------------------
2 files changed, 17 insertions(+), 49 deletions(-)
Index: linux-2.6-mm/include/linux/timex.h
===================================================================
--- linux-2.6-mm.orig/include/linux/timex.h
+++ linux-2.6-mm/include/linux/timex.h
@@ -90,7 +90,7 @@
* 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 */

Index: linux-2.6-mm/kernel/time/ntp.c
===================================================================
--- linux-2.6-mm.orig/kernel/time/ntp.c
+++ linux-2.6-mm/kernel/time/ntp.c
@@ -37,7 +37,7 @@ int tickadj = 500/HZ ? : 1; /* microsec
/* 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) */
@@ -63,6 +63,7 @@ void ntp_clear(void)
ntp_update_frequency();

tick_length = tick_length_base;
+ time_offset = 0;
}

#define CLOCK_TICK_OVERFLOW (LATCH * HZ - CLOCK_TICK_RATE)
@@ -89,7 +90,7 @@ 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;
@@ -157,42 +158,14 @@ 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);
}

/*
@@ -353,12 +326,8 @@ 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
@@ -372,8 +341,7 @@ 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;
@@ -388,6 +356,7 @@ 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)
@@ -401,9 +370,8 @@ leave: if ((time_status & (STA_UNSYNC|ST

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;
--

-
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