getnanotime(9) - NetBSD Manual Pages

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MICROTIME(9)           NetBSD 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 abstrac-
     tions which return a less precise, but faster to obtain, time.

     The intent of the getbintime(), getmicrotime(), and getnanotime() func-
     tions is to enforce the user's preference for timer accuracy versus exe-
     cution 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 mono-
     tonically increasing, it is always possible for the system clock to be
     manually reset by the system administrator to any date.

NetBSD 8.2                       May 13, 2013                       NetBSD 8.2