AUART_CTRL2_UARTEN
mxs_set(AUART_CTRL2_UARTEN, s, REG_CTRL2);
mxs_clr(AUART_CTRL2_UARTEN, s, REG_CTRL2);
mxs_set(AUART_CTRL2_UARTEN | AUART_CTRL2_TXE, s, REG_CTRL2);
if (!(mxs_read(s, REG_CTRL2) & AUART_CTRL2_UARTEN))