ttwrite
{ endrunopen, endrunclose, ttread, ttwrite, nullioctl,
{ ttyopen, ttylclose, ttread, ttwrite, nullioctl,
{ nmeaopen, nmeaclose, ttread, ttwrite, nullioctl,
{ mstsopen, mstsclose, ttread, ttwrite, nullioctl,
int ttwrite(struct tty *tp, struct uio *uio, int flag);