tv_add_micro
tv_add_micro(tvp, -usec);
tv_add_micro(tvp, (int)(offset * 1000000.0));
void tv_add_micro(struct timeval *tvp, long usec);
tv_add_micro(rtvp, (long)(tv_delta_double(&tv1, ltvp) * 1000000.0) / 2);