armv7l.h

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/*
        This implementation of an ARM v7 clock reader utilizes the
        Performance Monitoring Unit (PMU) on Cortex-A7 chips.
        Unfortunately, access to the cycle counter from userspace
        is disabled by default. A kernel module that enables access
        from userspace is required or the system will fault.

        An example kernel module that does just that can be found:
        https://github.com/nmcglohon/armv7l-userspace-counter.git

        More information can be found:
        http://neocontra.blogspot.com/2013/05/user-mode-performance-counters-for.html
 */

#ifndef INC_clock_armv7l
#define INC_clock_armv7l

typedef unsigned int tw_clock;

static inline tw_clock  tw_clock_read(void)
{
        unsigned int result;
#ifdef ROSS_timing
        do {
                __asm__ __volatile__ ("MRC p15, 0, %0, c9, c13, 0" : "=r"(result));
        } while (__builtin_expect ((int) result == -1, 0));
#endif

        return result;
}

#endif