42 lines
1.4 KiB
Text
42 lines
1.4 KiB
Text
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Time Interpolators
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------------------
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Time interpolators are a base of time calculation between timer ticks and
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allow an accurate determination of time down to the accuracy of the time
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source in nanoseconds.
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The architecture specific code typically provides gettimeofday and
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settimeofday under Linux. The time interpolator provides both if an arch
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defines CONFIG_TIME_INTERPOLATION. The arch still must set up timer tick
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operations and call the necessary functions to advance the clock.
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With the time interpolator a standardized interface exists for time
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interpolation between ticks. The provided logic is highly scalable
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and has been tested in SMP situations of up to 512 CPUs.
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If CONFIG_TIME_INTERPOLATION is defined then the architecture specific code
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(or the device drivers - like HPET) may register time interpolators.
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These are typically defined in the following way:
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static struct time_interpolator my_interpolator {
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.frequency = MY_FREQUENCY,
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.source = TIME_SOURCE_MMIO32,
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.shift = 8, /* scaling for higher accuracy */
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.drift = -1, /* Unknown drift */
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.jitter = 0 /* time source is stable */
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};
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void time_init(void)
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{
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....
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/* Initialization of the timer *.
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my_interpolator.address = &my_timer;
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register_time_interpolator(&my_interpolator);
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....
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}
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For more details see include/linux/timex.h and kernel/timer.c.
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Christoph Lameter <christoph@lameter.com>, October 31, 2004
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