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Introduce offset correction rate

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We want to correct the offset quickly, but we also want to keep the
frequency error caused by the correction itself low.

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.

This is only a suggestion and it's up to the system driver how the
adjustment will be executed.
This commit is contained in:
Miroslav Lichvar
2011-09-05 15:45:32 +02:00
parent 79e5f2be13
commit c7d0232bb1
13 changed files with 40 additions and 20 deletions
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22
reference.c
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@@ -541,6 +541,7 @@ REF_SetReference(int stratum,
IPAddr *ref_ip,
struct timeval *ref_time,
double offset,
double offset_sd,
double frequency,
double skew,
double root_delay,
@@ -556,6 +557,7 @@ REF_SetReference(int stratum,
double abs_freq_ppm;
double update_interval;
double elapsed;
double correction_rate;
struct timeval now;
assert(initialised);
@@ -611,6 +613,20 @@ REF_SetReference(int stratum,
}
last_ref_update = now;
/* We want to correct the offset quickly, but we also want to keep the
frequency error caused by the correction itself low.
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.
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;
/* Eliminate updates that are based on totally unreliable frequency
information */
@@ -645,7 +661,7 @@ REF_SetReference(int stratum,
our_residual_freq = new_freq - our_frequency;
maybe_log_offset(our_offset);
LCL_AccumulateFrequencyAndOffset(our_frequency, our_offset);
LCL_AccumulateFrequencyAndOffset(our_frequency, our_offset, correction_rate);
} else {
@@ -653,7 +669,7 @@ REF_SetReference(int stratum,
LOG(LOGS_INFO, LOGF_Reference, "Skew %f too large to track, offset=%f", skew, our_offset);
#endif
maybe_log_offset(our_offset);
LCL_AccumulateOffset(our_offset);
LCL_AccumulateOffset(our_offset, correction_rate);
our_residual_freq = frequency;
}
@@ -714,7 +730,7 @@ REF_SetManualReference
our_residual_freq = 0.0;
maybe_log_offset(offset);
LCL_AccumulateFrequencyAndOffset(frequency, offset);
LCL_AccumulateFrequencyAndOffset(frequency, offset, 0.0);
maybe_make_step();
abs_freq_ppm = LCL_ReadAbsoluteFrequency();