UART_IMSC_TXIM
bus_space_write_4(iot, ioh, UART_ICR, is & ~UART_IMSC_TXIM);
!ISSET(is, UART_IMSC_TXIM))
if (ISSET(is, UART_IMSC_TXIM) && ISSET(tp->t_state, TS_BUSY)) {
if (!ISSET(sc->sc_imsc, UART_IMSC_TXIM)) {
sc->sc_imsc |= UART_IMSC_TXIM;
if (ISSET(sc->sc_imsc, UART_IMSC_TXIM)) {
sc->sc_imsc &= ~UART_IMSC_TXIM;