NAME

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

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 version 2.16 and __ppc_get_timebase_freq() has been available since version 2.17.

CONFORMING TO

Both functions are nonstandard GNU extensions.

EXAMPLE

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 = __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);
}