TIMER_MUSECFREQ
#define TIMER_MUSECDIV(x) ((TIMER_MUSECFREQ+(x)/2)/(x))
= (Musec * TIMER_MUSECFREQ) +
(usec * (TIMER_MUSECFREQ >> 20)) +
((usec * ((TIMER_MUSECFREQ & ((1 <<20) - 1)) >>10)) >>10) +
((usec * (TIMER_MUSECFREQ & ((1 << 10) - 1))) >> 20);