IMXUART_SR2_RDR
if(!ISSET(bus_space_read_2(iot, ioh, IMXUART_USR2), IMXUART_SR2_RDR))
while(ISSET(bus_space_read_2(iot, ioh, IMXUART_USR2), IMXUART_SR2_RDR)) {
IMXUART_SR2_RDR) == 0)