armv7l.c

Go to the documentation of this file.

/*
        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
 */
 
#include <ross.h>
 
#ifndef __GNUC__
#  error gcc asm extensions required
#endif
#if ! (defined(__arm__))
#  error only 32 bit arm platform supported
#endif
 
static const tw_optdef clock_opts [] =
{
        TWOPT_GROUP("ROSS Timing"),
        TWOPT_STIME("clock-rate", g_tw_clock_rate, "CPU Clock Rate"),
        TWOPT_END()
};
 
const tw_optdef *tw_clock_setup(void)
{
        return clock_opts;
}
 
 
void tw_clock_init(tw_pe * me)
{
        me->clock_time = 0;
        me->clock_offset = tw_clock_read();
}
 
 
tw_clock tw_clock_now(tw_pe * me)
{
        me->clock_time = tw_clock_read() - me->clock_offset;
        return me->clock_time;
}