SEC_TO_US
end = start + SEC_TO_US(timeout_sec);
end = start - SEC_TO_US(btp.tv_sec + 1);
return SEC_TO_US((uint64_t)tv.tv_sec) + tv.tv_usec;
end = start - SEC_TO_US(timeout_sec);
NOTE_USECONDS, SEC_TO_US(1), (void *)1);
if (elapsed > SEC_TO_US(1))