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Add corrtimeratio directive

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The corrtimeratio directive controls the ratio between the
duration in which the clock is slewed for an average correction
according to the source history and the interval in which the
corrections are done (usually the NTP polling interval).  Corrections
larger than the average take less time and smaller corrections take
more time, the amount of the correction and the correction time are
inversely proportional.

Increasing corrtimeratio makes the overall frequency error of
the system clock smaller, but increases the overall time error as
the corrections will take longer.

By default, the ratio is 1, which means the duration of an average
correction will be close to the update interval.
This commit is contained in:
Miroslav Lichvar
2011-11-15 12:24:50 +01:00
parent 1b8deaf354
commit 9a01ccc07f
4 changed files with 60 additions and 3 deletions
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11
reference.c
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@@ -56,6 +56,8 @@ static double our_root_dispersion;
static double max_update_skew;
static double correction_time_ratio;
/* Flag indicating that we are initialised */
static int initialised = 0;
@@ -181,6 +183,8 @@ REF_Initialise(void)
max_update_skew = fabs(CNF_GetMaxUpdateSkew()) * 1.0e-6;
correction_time_ratio = CNF_GetCorrectionTimeRatio();
enable_local_stratum = CNF_AllowLocalReference(&local_stratum);
CNF_GetMakeStep(&make_step_limit, &make_step_threshold);
@@ -619,13 +623,14 @@ REF_SetReference(int stratum,
Define correction rate as the area of the region bounded by the graph of
offset corrected in time. Set the rate so that the time needed to correct
an offset equal to the current sourcestats stddev will be equal to the
update interval (assuming linear adjustment). The offset and the
time needed to make the correction are inversely proportional.
update interval multiplied by the correction time ratio (assuming linear
adjustment). The offset and the time needed to make the correction are
inversely proportional.
This is only a suggestion and it's up to the system driver how the
adjustment will be executed. */
correction_rate = 0.5 * offset_sd * update_interval;
correction_rate = correction_time_ratio * 0.5 * offset_sd * update_interval;
/* Eliminate updates that are based on totally unreliable frequency
information */