EFM32

usart.c

USART_InitAsync_TypeDef init = USART_INITASYNC_DEFAULT;
init.enable = usartDisable;

CMU_ClockEnable(cmuClock_USART1, true);

GPIO_PinModeSet(gpioPortD, 0, gpioModePushPull, 1);
GPIO_PinModeSet(gpioPortD, 1, gpioModeInput, 0);

USART_InitAsync(USART, &init);
USART->ROUTE = USART_ROUTE_LOCATION_LOC1 | USART_ROUTE_RXPEN | USART_ROUTE_TXPEN;
USART->CTRL = USART_CTRL_AUTOTX;

USART_IntClear(USART, _USART_IF_MASK);
USART_IntEnable(USART, USART_IF_RXDATAV);

USART_Enable(USART, usartEnable);