EFM32 Giant Gecko, Interrupt procedure not working - c

Question

I am using a EFM32 Giant Gecko 3700 starter kit for basic UART echoing.
When i echo RX to TX in a while(1) loop in my main function it works. However when i want to use the interrupt function, it no longer works. Checking the registers shows that my data is being read correctly, it just does not send it back.
My code:
#include "efm32gg990f1024.h"
#include "em_chip.h" // required for CHIP_Init() function
#include <string.h>
#define COM_PORT 3 // gpioPortD (USART location #1: PD0 and PD1)
#define UART_TX_pin 0
char rx_char = 0; // Temp variable for storing received characters
int main() {
CHIP_Init(); // This function addresses some chip errata and should be called at the start of every EFM32 application (need em_system.c)
uint8_t i;
char test_string[] = "\n\rHello World!\n\r";
CMU->CTRL |= (1 << 14); // Set HF clock divider to /2 to keep core frequency <32MHz
CMU->OSCENCMD |= 0x4; // Enable XTAL Oscillator
while(! (CMU->STATUS & 0x8) ); // Wait for XTAL osc to stabilize
CMU->CMD = 0x2; // Select HF XTAL osc as system clock source. 48MHz XTAL, but we divided the system clock by 2, therefore our HF clock should be 24MHz
CMU->HFPERCLKEN0 = (1 << 13) | (1 << 1); // Enable GPIO, and USART1 peripheral clocks
GPIO->P[COM_PORT].MODEL = (1 << 4) | (4 << 0); // Configure PD0 as digital output and PD1 as input
GPIO->P[COM_PORT].DOUTSET = (1 << UART_TX_pin); // Initialize PD0 high since UART TX idles high (otherwise glitches can occur)
// Use default value for USART1->CTRL: asynch mode, x16 OVS, lsb first, CLK idle low
// Default frame options: 8-none-1-none
USART1->CLKDIV = (48 << 6); // 48 will give 115200 baud rate (using 16-bit oversampling with 24MHz peripheral clock)
USART1->CMD = (1 << 11) | (1 << 10) | (1 << 2) | (1 << 0); // Clear RX/TX buffers and shif regs, Enable Transmitter and Receiver
USART1->IFC = 0x1FF9; // clear all USART interrupt flags
USART1->ROUTE = 0x103; // Enable TX and RX pins, use location #1 (UART TX and RX located at PD0 and PD1, see EFM32GG990 datasheet for details)
// Print test string
for(i=0; i<strlen(test_string); i++) {
while( !(USART1->STATUS & (1 << 6)) ); // wait for TX buffer to empty
USART1->TXDATA = test_string[i]; // print each character of the test string
}
while(1) {
// what used to be in main loop
/*
if(USART1->STATUS & (1 << 7)) { // if RX buffer contains valid data
rx_char = USART1->RXDATA; // store the data
}
if(rx_char) { // if we have a valid character
if(USART1->STATUS & (1 << 6)) { // check if TX buffer is empty
USART1->TXDATA = rx_char; // echo received char
rx_char = 0; // reset temp variable
}
}
*/
}
}
void USART1_RX_IRQHandler(void)
{
if(USART1->STATUS & (1 << 7)) { // if RX buffer contains valid data
rx_char = USART1->RXDATA; // store the data
}
if(rx_char) { // if we have a valid character
if(USART1->STATUS & (1 << 6)) { // check if TX buffer is empty
USART1->TXDATA = rx_char; // echo received char
rx_char = 0; // reset temp variable
}
}
}

Answer 1

You forgot to enable the interrupt vector in the NVIC, and also in the USART.
USART1->IEN = USART_IEN_RXDATAV;
NVIC_EnableIRQ(USART1_RX_IRQn);