ref: 4a40fbd789b5308e3904cb73b164f3f8f270c4d0
dir: /nanosec.c/
#include <u.h>
#include <libc.h>
#include <tos.h>
/*
* nsec() is wallclock and can be adjusted by timesync
* so need to use cycles() instead, but fall back to
* nsec() in case we can't
*/
u64int
nanosec(void)
{
static u64int fasthz, xstart;
u64int x, div;
if(fasthz == ~0ULL)
return nsec() - xstart;
if(fasthz == 0){
if(_tos->cyclefreq){
fasthz = _tos->cyclefreq;
cycles(&xstart);
} else {
fasthz = ~0ULL;
xstart = nsec();
}
return 0;
}
cycles(&x);
x -= xstart;
/* this is ugly */
for(div = 1000000000ULL; x < 0x1999999999999999ULL && div > 1 ; div /= 10ULL, x *= 10ULL);
return x / (fasthz / div);
}