56 lines
1.9 KiB
C
56 lines
1.9 KiB
C
#ifndef __MONOTONIC_H
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#define __MONOTONIC_H
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/* The monotonic clock is an always increasing clock source. It is unrelated to
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* the actual time of day and should only be used for relative timings. The
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* monotonic clock is also not guaranteed to be chronologically precise; there
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* may be slight skew/shift from a precise clock.
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*
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* Depending on system architecture, the monotonic time may be able to be
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* retrieved much faster than a normal clock source by using an instruction
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* counter on the CPU. On x86 architectures (for example), the RDTSC
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* instruction is a very fast clock source for this purpose.
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*/
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#include "fmacros.h"
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#include <stdint.h>
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#include <unistd.h>
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/* A counter in micro-seconds. The 'monotime' type is provided for variables
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* holding a monotonic time. This will help distinguish & document that the
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* variable is associated with the monotonic clock and should not be confused
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* with other types of time.*/
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typedef uint64_t monotime;
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/* Retrieve counter of micro-seconds relative to an arbitrary point in time. */
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extern monotime (*getMonotonicUs)(void);
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/* Call once at startup to initialize the monotonic clock. Though this only
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* needs to be called once, it may be called additional times without impact.
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* Returns a printable string indicating the type of clock initialized.
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* (The returned string is static and doesn't need to be freed.) */
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#ifdef __cplusplus
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extern "C"
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#endif
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const char * monotonicInit();
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/* Functions to measure elapsed time. Example:
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* monotime myTimer;
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* elapsedStart(&myTimer);
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* while (elapsedMs(myTimer) < 10) {} // loops for 10ms
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*/
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static inline void elapsedStart(monotime *start_time) {
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*start_time = getMonotonicUs();
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}
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static inline uint64_t elapsedUs(monotime start_time) {
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return getMonotonicUs() - start_time;
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}
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static inline uint64_t elapsedMs(monotime start_time) {
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return elapsedUs(start_time) / 1000;
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}
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#endif
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