MICROTIME(9)

MICROTIME(9) | Kernel Developer's Manual | MICROTIME(9)

# NAME

bintime, getbintime, microtime, getmicrotime, nanotime, getnanotime — get the current time

# SYNOPSIS

#include <sys/time.h>

void
bintime(struct bintime *bt);

void
getbintime(struct bintime *bt);

void
microtime(struct timeval *tv);

void
getmicrotime(struct timeval *tv);

void
nanotime(struct timespec *tsp);

void
getnanotime(struct timespec *tsp);

# DESCRIPTION

The bintime() and getbintime() functions store the system time as a struct bintime at the addresses specified by bt. The microtime() and getmicrotime() functions perform the same utility, but record the time as a struct timeval instead. Similarly the nanotime() and getnanotime() functions store the time as a struct timespec. The structures are described in timeval(3).

The bintime(), microtime(), and nanotime() functions always query the timecounter to return the current time as precisely as possible. Whereas getbintime(), getmicrotime(), and getnanotime() functions are abstractions which return a less precise, but faster to obtain, time.

The intent of the getbintime(), getmicrotime(), and getnanotime() functions is to enforce the user's preference for timer accuracy versus execution time. They should be used where a precision of 1/HZ (e.g., 10 msec on a 100HZ machine, see hz(9)) is acceptable or where performance is priority.

The system realtime clock is guaranteed to be monotonically increasing at all times. As such, all calls to these functions are guaranteed to return a system time greater than or equal to the system time returned in any previous calls. Comparable functions exist to retrieve the time elapsed since boot; see microuptime(9).

# CODE REFERENCES

The implementation of the microtime() family of functions is in sys/kern/kern_tc.c as a part of the timecounter(9) framework.

The implementation of the time counter sources used by the timecounter(9) is machine dependent, hence its location in the source code tree varies from architecture to architecture.

# SEE ALSO

settimeofday(2), bintime_add(9), inittodr(9), time_second(9), tvtohz(9)

# AUTHORS

This manual page was written by Jeremy Cooper and Kelly Yancey <kbyanc@posi.net>.

# CAVEATS

Despite the guarantee that the system realtime clock will always be monotonically increasing, it is always possible for the system clock to be manually reset by the system administrator to any date.

May 13, 2013 | NetBSD 7.1