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.
struct timecounter *
)
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.
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/kern/kern_tc.c
.
The
bintime
structure and related functions are defined in the file
sys/sys/time.h
.