Most PHC drivers implement stepping (ADJ_SETOFFSET) by reading the
clock, adjusting the value by the offset and writing it back. This is
not perfectly accurate and if the operation is slow (e.g. due to PCIe
latencies), the error can be in microseconds.
Increase the default first step threshold from 100 nanoseconds to 20
microseconds to step only when the initial offset is larger than
the error in the step.
Signed-off-by: Miroslav Lichvar <mlichvar@redhat.com>
With the new linreg servo the frequency offset and time offset are
controlled separately. The ratio between master's frequency and the
current frequency of the local clock is known and can be used when
calculating delay or peer delay to improve their accuracy.
This greatly improves the stability of the delay when the servo is
correcting a large offset.
Signed-off-by: Miroslav Lichvar <mlichvar@redhat.com>
This servo uses linear regression to estimate current time and
frequency error. The number of points used in the regression is
variable (from 4 to 64 in powers of 2) and is selected by a long-term
statistic of the prediction error.
Future improvements could include tracking of sudden frequency changes
(e.g. due to temperature variations), better stability of the error
statistic when a large offset is corrected, options to set the speed of
the adaptation, minimum and maximum number of points, or an option to
prefer frequency accuracy over time accuracy.
Signed-off-by: Miroslav Lichvar <mlichvar@redhat.com>
These settings will be useful for all implemented servos, so move them
to the common servo code to avoid duplication. The configuration options
are renamed, but the they can be still set by their old names.
Signed-off-by: Miroslav Lichvar <mlichvar@redhat.com>
This patch adds a new servo method to let the algorithm know about the
master clock's reported sync message interval. This information can be
used by the servo to adapt its synchronization parameters.
Signed-off-by: Richard Cochran <richardcochran@gmail.com>
Current date stored in nanoseconds doesn't fit in 64-bit double format.
Keep the offset and the time stamp in integer nanoseconds.
Signed-off-by: Miroslav Lichvar <mlichvar@redhat.com>
passing a string as the servo type seems ugly when there are only a few
choices. This patch modifies the servo_create to take an enum instead.
Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
If software time stamping is to be used, then the servo will want to
have appropriate filtering.
Signed-off-by: Richard Cochran <richardcochran@gmail.com>
Miroslav Lichvar
Richard Cochran
Jacob Keller