mstohz(9) [netbsd man page]

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

NAME

     mstohz, hztoms -- convert between milliseconds and system clock ticks

SYNOPSIS

     #include <sys/param.h>

     int
     mstohz(int ms);

     int
     hztoms(int hz);

DESCRIPTION

     The mstohz() macro can be used to convert time in milliseconds to system clock ticks, as used by the callout(9) facility, in an integer-over-
     flow safe way.  Conversely, hztoms() converts system clock ticks to milliseconds.

     These macros are defined in the <sys/param.h> header.  Individual ports can have a processor-specific, more efficient version implemented in
     their <machine/param.h> header as a define.

RETURN VALUES

     The return value is either the number of clock ticks or milliseconds for the specified value.

SEE ALSO

     param(3), callout(9), tvtohz(9)

BUGS

     Neither mstohz() nor hztoms() make use of expensive 64-bit integer arithmetic.  The result from mstohz() will be rounded down to one second
     if the parameter is larger than 131072 milliseconds.

BSD
								 October 20, 2011							       BSD

timeout(9r)															       timeout(9r)

NAME

       timeout - General: Initializes a callout queue element

SYNOPSIS

       void timeout(
	       int (*function) (),
	       caddr_t argument,
	       register int time );

ARGUMENTS

       Specifies  a pointer to the routine to be called.  Specifies a single argument to be passed to the called routine.  Specifies the amount of
       time to delay before calling the specified routine. You express time as time (in seconds) * hz.

DESCRIPTION

       The timeout routine initializes a callout queue element to make it easy to execute the specified routine at the time specified in the  time
       argument.  You often use callout routines for infrequent polling or error handling. The routine you specify will be called on the interrupt
       stack (not in processor context) as dispatched from the softclock routine.

       The global variable hz contains the number of clock ticks per second. This variable is a second's worth of clock ticks.

       Thus, if you wanted a 4-minute timeout, you would pass 4 * 60 * hz as the third argument to the timeout routine as follows:

	/* A 4-minute timeout */
	.
	.
	.
	timeout(lptout, (caddr_t)dev, 4 * 60 * hz);

NOTES

       The granularity of the time delay is dependent on the hardware. For example, the granularity of some Alpha CPUs is  1024  clock	ticks  per
       second.	 Other	Alpha  CPUs  have  a granularity of 1200 clock ticks per second. Still other Alpha CPUs exhibit a granularity of 128 clock
       ticks per second.  Because the granularity of the time delay is dependent on the hardware, the operating system provides the hz	and  lbolt
       global  variables.  Use	the  hz  global variable to determine the number of clock ticks per second for a specific Alpha CPU. Use the lbolt
       global variable as a periodic wakeup mechanism.

RETURN VALUES

       None

SEE ALSO

       Routines: untimeout(9r)

																       timeout(9r)