__ppc_get_timebase

NAME

__ppc_get_timebase, __ppc_get_timebase_freq - get the current value of the Time Base Register on Power architecture and its frequency.

LIBRARY

Standard C library (libc, -lc)

SYNOPSIS

#include <sys/platform/ppc.h>

uint64_t __ppc_get_timebase(void);
uint64_t __ppc_get_timebase_freq(void);

DESCRIPTION

__ppc_get_timebase() reads the current value of the Time Base Register and returns its value, while __ppc_get_timebase_freq() returns the frequency in which the Time Base Register is updated.

The Time Base Register is a 64-bit register provided by Power Architecture processors. It stores a monotonically incremented value that is updated at a system-dependent frequency that may be different from the processor frequency.

RETURN VALUE

__ppc_get_timebase() returns a 64-bit unsigned integer that represents the current value of the Time Base Register.

__ppc_get_timebase_freq() returns a 64-bit unsigned integer that represents the frequency at which the Time Base Register is updated.

VERSIONS

GNU C Library support for __ppc_get_timebase() has been provided since glibc 2.16 and __ppc_get_timebase_freq() has been available since glibc 2.17.

STANDARDS

Both functions are nonstandard GNU extensions.

EXAMPLES

The following program will calculate the time, in microseconds, spent between two calls to __ppc_get_timebase().

Program source

#include <inttypes.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/platform/ppc.h>

/* Maximum value of the Time Base Register: 2^60 - 1.
Source: POWER ISA. */
#define MAX_TB 0xFFFFFFFFFFFFFFF

int
main(void)
{
uint64_t tb1, tb2, diff;
uint64_t freq;

freq = __ppc_get_timebase_freq();
printf("Time Base frequency = %"PRIu64" Hz\n", freq);

tb1 = __ppc_get_timebase();

// Do some stuff...

tb2 = __ppc_get_timebase();

if (tb2 > tb1) {
diff = tb2 - tb1;
} else {
/* Treat Time Base Register overflow. */
diff = (MAX_TB - tb2) + tb1;
}

printf("Elapsed time = %1.2f usecs\n",
(double) diff * 1000000 / freq);

exit(EXIT_SUCCESS);
}

SEE ALSO

time(2), usleep(3)