TIMECOUNTER(9) | Kernel Developer's Manual | TIMECOUNTER(9) |
timecounter
, tc_init
—
#include <sys/timetc.h>
void
tc_init
(struct
timecounter *tc);
A timecounter is a binary counter which has two properties:
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.
(*tc_get_timecount)
(struct
timecounter *)(*tc_poll_pps)
(struct timecounter
*)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.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.
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.
<sys/time.h>
.
Poul-Henning Kamp, Timecounters: Efficient and precise timekeeping in SMP kernels, Proceedings of EuroBSDCon 2002, Amsterdam, http://phk.freebsd.dk/pubs/timecounter.pdf, 15-17 November, 2002.
June 8, 2010 | NetBSD 9.0 |