TC_INIT(9) OpenBSD Kernel Manual TC_INIT(9)NAMEtc_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 tracking
time.
A timecounter is a binary counter which has two properties:
o it runs at a fixed, known frequency
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;
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 null-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.
CODE REFERENCES
The timecounter framework is implemented in the file sys/kern/kern_tc.c.
SEE ALSOamdpm(4), elansc(4), gscpm(4), ichpcib(4), viaenv(4), hz(9), microtime(9)
Poul-Henning Kamp, "Timecounter: Efficient and precise timekeeping in SMP
kernels", http://phk.freebsd.dk/pubs/timecounter.pdf, The FreeBSD
Project.
HISTORY
The timecounter interface first appeared in OpenBSD 3.6.
OpenBSD 4.9 May 31, 2007 OpenBSD 4.9