Commit | Line | Data |
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1da177e4 LT |
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 |