hardclock(9) [netbsd man page]

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

NAME

     hardclock -- real-time timer

SYNOPSIS

     void
     hardclock(struct clockframe *frame);

DESCRIPTION

     The hardclock() function is called hz(9) times per second.  It implements the real-time system clock.  The argument frame is an opaque,
     machine-dependent structure that encapsulates the previous machine state.

     The hardclock() performs different tasks such as:

	   o   Run the current process's virtual and profile time (decrease the corresponding timers, if they are activated, and generate
	       SIGVTALRM or SIGPROF, respectively).

	   o   Increment the time-of-day, taking care of any ntpd(8) or adjtime(2) induced changes and leap seconds, as well as any necessary com-
	       pensations to keep in sync with PPS signals or external clocks, if support for this is in the kernel (see options(4)).

	   o   Schedule softclock interrupts if any callouts should be triggered (see callout(9)).

SEE ALSO

     adjtime(2), ntp_adjtime(2), signal(7), ntpd(8), callout(9), hz(9)

BSD
								  March 25, 2010							       BSD

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

NAME

     hz, tick, tickadj, stathz, profhz -- system time model

SYNOPSIS

     #include <sys/kernel.h>

     extern int hz;
     extern int tick;
     extern int tickadj;
     extern int stathz;
     extern int profhz;

DESCRIPTION

     The essential clock handling routines in NetBSD are written to operate with two timers that run independently of each other.  The main clock,
     running hz times per second, is used to keep track of real time.

     In another words, hz specifies the number of times the hardclock(9) timer ticks per second.  Normally hardclock(9) increments time by tick
     each time it is called.  If the system clock has drifted, adjtime(2) may be used to skew this increment based on the rate of tickadj.

     The second timer is used to gather timing statistics.  It also handles kernel and user profiling.	If the second timer is programmable, it is
     randomized to avoid aliasing between the two clocks.  The mean frequency of the second timer is stathz.  If a separate clock is not avail-
     able, stathz is set to hz.

     If profiling is enabled, the clock normally used to drive stathz may be run at a higher rate profhz, which is required to be a multiple of
     stathz.  This will give higher resolution profiling information.

     These system variables are also available as struct clockinfo from sysctl(3) and kern.clockrate from sysctl(8).  The hz is hardware-depen-
     dent; it can be overridden (if the machine dependent code supports this) by defining HZ in the kernel configuration file (see options(4)).
     Only override the default value if you really know what you are doing.

SEE ALSO

     adjtime(2), callout(9), hardclock(9), microtime(9), time_second(9)

BSD
								  March 25, 2010							       BSD