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1 | Time Interpolators | ||
2 | ------------------ | ||
3 | |||
4 | Time interpolators are a base of time calculation between timer ticks and | ||
5 | allow an accurate determination of time down to the accuracy of the time | ||
6 | source in nanoseconds. | ||
7 | |||
8 | The architecture specific code typically provides gettimeofday and | ||
9 | settimeofday under Linux. The time interpolator provides both if an arch | ||
10 | defines CONFIG_TIME_INTERPOLATION. The arch still must set up timer tick | ||
11 | operations and call the necessary functions to advance the clock. | ||
12 | |||
13 | With the time interpolator a standardized interface exists for time | ||
14 | interpolation between ticks. The provided logic is highly scalable | ||
15 | and has been tested in SMP situations of up to 512 CPUs. | ||
16 | |||
17 | If CONFIG_TIME_INTERPOLATION is defined then the architecture specific code | ||
18 | (or the device drivers - like HPET) may register time interpolators. | ||
19 | These are typically defined in the following way: | ||
20 | |||
21 | static struct time_interpolator my_interpolator { | ||
22 | .frequency = MY_FREQUENCY, | ||
23 | .source = TIME_SOURCE_MMIO32, | ||
24 | .shift = 8, /* scaling for higher accuracy */ | ||
25 | .drift = -1, /* Unknown drift */ | ||
26 | .jitter = 0 /* time source is stable */ | ||
27 | }; | ||
28 | |||
29 | void time_init(void) | ||
30 | { | ||
31 | .... | ||
32 | /* Initialization of the timer *. | ||
33 | my_interpolator.address = &my_timer; | ||
34 | register_time_interpolator(&my_interpolator); | ||
35 | .... | ||
36 | } | ||
37 | |||
38 | For more details see include/linux/timex.h and kernel/timer.c. | ||
39 | |||
40 | Christoph Lameter <christoph@lameter.com>, October 31, 2004 | ||
41 | |||