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timecounter(9) [netbsd man page]

TIMECOUNTER(9)						   BSD Kernel Developer's Manual					    TIMECOUNTER(9)

timecounter, tc_init -- machine-independent binary timescale SYNOPSIS
#include <sys/timetc.h> void tc_init(struct timecounter *tc); DESCRIPTION
The timecounter interface is a machine-independent implementation of a binary timescale using whatever hardware support is at hand for track- ing time. A timecounter is a binary counter which has two properties: o it runs at a fixed, known frequency; and o it has sufficient bits to not roll over in less than approximately max(2 msec, 2/HZ seconds) (the value 2 here is really 1 + delta, for some indeterminate value of delta). The interface between the hardware which implements a timecounter and the machine-independent code which uses this to keep track of time is a timecounter structure: struct timecounter { timecounter_get_t *tc_get_timecount; timecounter_pps_t *tc_poll_pps; u_int tc_counter_mask; u_int64_t tc_frequency; const char *tc_name; int tc_quality; void *tc_priv; struct timecounter *tc_next; } The fields of the timecounter structure are described below. u_int (*tc_get_timecount)(struct timecounter *) This function reads the counter. It is not required to mask any unimplemented bits out, as long as they are constant. void (*tc_poll_pps)(struct timecounter *) This function is optional and can be set to NULL. It will be called whenever the timecounter is rewound, and is intended to check for PPS events. Normal hardware does not need it but timecounters which latch PPS in hardware do. tc_counter_mask This mask should mask off any unimplemented bits. tc_frequency Frequency of the counter in Hz. tc_name Name of the timecounter. Can be any NUL-terminated string. tc_quality Used to determine if this timecounter is better than another timecounter - higher means better. Negative means ``only use at explicit request''. tc_priv Pointer to the timecounter's private parts. tc_next For internal use. To register a new timecounter, the hardware device driver should fill a timecounter structure with appropriate values and call the tc_init() function, giving a pointer to the structure as a tc parameter. TIMESTAMP FORMAT
The timestamp format used in the machine independent timecounter implementation is a bintime structure: struct bintime { time_t sec; uint64_t frac; } The sec field records the number of seconds as well as the tv_sec field in the traditional UNIX timeval and timespec structures, described in timeval(3). The frac field records fractional seconds represented in a fully 64 bit integer, i.e. it goes all the way from 0 through 0xFFFFFFFFFFFFFFFF per each second. The effective resolution of the frac value depends on a frequency of the machine dependent timecounter source. The bintime format is a binary number, not a pseudo-decimal number, so it can be used as a simple binary counter without expensive 64 bit arithmetics. CODE REFERENCES
The timecounter framework is implemented in the file sys/kern/kern_tc.c. The bintime structure and related functions are defined in the file <sys/time.h>. SEE ALSO
clock_settime(2), ntp_adjtime(2), settimeofday(2), bintime(9), bintime_add(9), binuptime(9), hz(9), time_second(9) Poul-Henning Kamp, "Timecounters: Efficient and precise timekeeping in SMP kernels", Proceedings of EuroBSDCon 2002, Amsterdam,, 15-17 November, 2002. HISTORY
The timecounter interface first appeared in FreeBSD, and was ported to NetBSD 4.0 by Frank Kardel and Simon Burge. BSD
June 8, 2010 BSD

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

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 *ts); 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 perfor- mance 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). SEE ALSO
settimeofday(2), bintime_add(9), inittodr(9), time_second(9), tvtohz(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. AUTHORS
This manual page was written by Jeremy Cooper and Kelly Yancey <>. BUGS
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. BSD
June 8, 2010 BSD
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