ref: 2e6f158f4dc9ebc6eb826041254221cba57c4019
dir: /sys/src/cmd/vmx/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
*/
uvlong
nanosec(void)
{
static uvlong fasthz, xstart;
uvlong x, div;
if(fasthz == ~0ULL)
return nsec() - xstart;
if(fasthz == 0){
if((fasthz = _tos->cyclefreq) == 0){
fasthz = ~0ULL;
xstart = nsec();
fprint(2, "cyclefreq not available, falling back to nsec()\n");
fprint(2, "you might want to disable aux/timesync\n");
return 0;
}else{
cycles(&xstart);
}
}
cycles(&x);
x -= xstart;
/* this is ugly */
for(div = 1000000000ULL; x < 0x1999999999999999ULL && div > 1 ; div /= 10ULL, x *= 10ULL);
return x / (fasthz / div);
}