harvey/sys/man/9/seconds

.TH SECONDS 9
.SH NAME
seconds, ticks, fastticks, HZ, MS2HZ, MS2TK, TK2MS, TK2SEC \- kernel times and time conversions
.SH SYNOPSIS
.ta \w'\fL#define 'u
.B
long	seconds(void)
.PP
.B
m->ticks
.br
MACHP(0)->ticks
.PP
.B
vlong   	fastticks(uvlong *hz)
.PP
.EX
#define	HZ          ...
#define	MS2HZ(t)    ...
#define	TK2SEC(t)   ...
#define	TK2MS(t)    ...
#define	MS2TK(m)    ...
.EE
.SH DESCRIPTION
.I Seconds
returns the system's idea of the current time as the number of seconds
since the start of the epoch
(00:00:00 GMT, January 1, 1970).
.PP
The
.B ticks
field of the
.B Mach
structure pointed to by
.B m
returns the number of system-dependent clock ticks on the
given processor since system boot.
On a multiprocessor,
.B MACHP(0)
is sometimes used to provide a reference time, since the tick value
might vary slightly across processors.
.PP
.I Fastticks
returns the number of ticks since boot as measured by the
fastest clock provided by the platform.
The frequency of the clock, in ticks per second,
is returned through
.IR hz ,
unless it is nil.
.PP
The system clock frequencies are platform-dependent.
Several symbolic constants and macro functions are defined by
the file
.B mem.h
to convert between different time units:
.TF TK2SEC(t)
.PD
.TP
.B HZ
The number of clock ticks per second.
.TP
.B MS2HZ
Milliseconds per clock tick.
.TP
.BI TK2SEC( t )
Convert
.I t
clock ticks to seconds and return the result (truncating not rounding).
.TP
.BI TK2MS( t )
Convert
.I t
clock ticks to milliseconds and return the result.
.TP
.BI MS2TK( m )
Convert
.I m
milliseconds to clock ticks and return the result (truncating).
.PP
The functions are often used to calculate delays for timing functions,
for instance:
.IP
.EX
if(atactlrwait(dp->cp, DHmagic, 0, MS2TK(100))){
	...
}
.EE
.SH SOURCE
.B /sys/src/9/*/mem.h
.br
.B /sys/src/9/*/clock.c
.br
.B /sys/src/9/port/tod.c