NAME

getusclk, usclk_init − get/init microsecond clock

SYNOPSIS

C syntax:

#include <usclkc.h>
void usclk_init()

usclk_t getusclk()

FORTRAN syntax:

$INCLUDE /usr/include/usclkf.h
subroutine usclk_init()

integer∗4 function getusclk()

Pascal syntax:

{$I /usr/include/usclkp.h}
procedure usclk_init;
cexternal;

function getusclk : longint;
cexternal;

DESCRIPTION

The Sequent microsecond clock (usclk) is a programmatically accessible 32-bit up-counter which increments in real (wall clock) time at a one microsecond per tick rate.  It is reset to zero at power-up and free runs thereafter.  There is no notification as the clock rolls over its maximum value and returns to zero. 

Usclk_init maps the microsecond clock into process address space, making it accessible for subsequent use.  Usclk_init should be called only once and must precede the first call to getusclk . 

Getusclk returns the current 32-bit microsecond clock value. 

The routines described here are in /usr/lib/libseq.a.  They are linked into a program using the −lseq option in the cc, fortran, pascal, or ld command line.  See the /usr/sequent/usclk.demo directory for sample usage. 

NOTES

The mapping established by usclk_init is inherited by forked processes. 

The call overhead for getusclk is almost nil on Symmetry, approximately 25 microseconds on Balance. 

DIAGNOSTICS

Usclk_init fails with exit status 1 if it cannot open, map, or access the microsecond clock device. 

On Balance, a SIGBUS access error signal is delivered if the microsecond clock device is improperly accessed (this cannot happen if getusclk(3) is used).

SEE ALSO

getitimer(2), gettimeofday(2)

BUGS

(Balance only.)  A slight chance exists that a user-mode program making an improper access to the microsecond clock device will cause a DYNIX panic.  No panic occurs if the device is accessed exclusively with the software interfaces provided for it. 

DYNIX