ref: 53fa826a8a695bcfade5c47f636f719c71e96b98
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(_tos->cyclefreq){ cycles(&xstart); fasthz = _tos->cyclefreq; } else { xstart = nsec(); fasthz = ~0ULL; fprint(2, "cyclefreq not available, falling back to nsec()\n"); fprint(2, "you might want to disable aux/timesync\n"); return 0; } } cycles(&x); x -= xstart; /* this is ugly */ for(div = 1000000000ULL; x < 0x1999999999999999ULL && div > 1 ; div /= 10ULL, x *= 10ULL); return x / (fasthz / div); }