Messages in this thread | | | From | "Ulrich Windl" <> | Date | Thu, 16 Sep 2004 09:02:03 +0200 | Subject | Re: [RFC][PATCH] new timeofday core subsystem (v.A0) |
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On 15 Sep 2004 at 11:48, john stultz wrote:
> NTP adjustments need to be applied smoothly and consistently as time > progresses. Adjustment to the NTP parameters occur at do_adjtimex and at
Actually I think (constant) NTP adjustments need to be applied any time. That's why I even tried to correct the TSC interpolation between ticks (If you visit the PPSkit patch, that's the "nanoscale" thing). The "constant adjustment values" are updated regularly also (per tick, per second, per NTP update).
The basic thought was: If the time between two ticks is not 1/HZ the TSC interpolation (that is calibrated against the timer ticks) also will not interpolate between 1/HZ ticks. I assumed the TSC interpolations is wrong by the same percentage the timer interrupts are. Thus I tried to reversely apply the frequency error learnt through NTP even to the TSC interpolation (in addition to the time increments every tick). My code however has the problem that I ran out of significant bits during several muliplies and divides, while supporting that maximum imaginable frequency range for TSC. Even with the best oscillator, it won't reach single nanosecond precision as I don't have enough bits for them.
Regards, Ulrich
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