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