EFM32 Happy Gecko ARM Cortex M0+

UART API

for EFM32 Happy Gecko ARM Cortex M0+

#include "em_system.h"

#include "em_chip.h"

#include "em_cmu.h"

#include "em_gpio.h"

#include "em_usart.h"

#define COM_PORT gpioPortC

#define TX_PIN   0

#define RX_PIN   1

const char test_string[] = "\n\EFM32 Happy Gecko!\n\r";

char rx_char;

int main () {

   

  uint8_t i;

  CHIP_Init();

   

  CMU_OscillatorEnable(cmuOsc_HFXO, true, true);          // enable HF XTAL osc and wait for it to stabilize

  CMU_ClockSelectSet(cmuClock_HF, cmuSelect_HFXO);        // select HF XTAL osc as system clock source (24MHz)

   

  CMU_ClockEnable(cmuClock_GPIO, true);                   // enable GPIO peripheral clock

  CMU_ClockEnable(cmuClock_USART1, true);                 // enable USART1 peripheral clock

   

  GPIO_PinModeSet(COM_PORT, TX_PIN, gpioModePushPull, 1); // set TX pin to push-pull output, initialize high (otherwise glitches can occur)

  GPIO_PinModeSet(COM_PORT, RX_PIN, gpioModeInput, 0);    // set RX pin as input (no filter)

   

  USART_InitAsync_TypeDef uartInit =

  {

    .enable = usartDisable,     // wait to enable transmitter and receiver

    .refFreq = 0,               // setting refFreq to 0 will invoke the CMU_ClockFreqGet() function and measure the HFPER clock

    .baudrate = 115200,         // desired baud rate

    .oversampling = usartOVS16, // set oversampling to x16

    .databits = usartDatabits8, // 8 data bits

    .parity = usartNoParity,    // no parity bits

    .stopbits = usartStopbits1, // 1 stop bit

    .mvdis = false,             // use majority voting

    .prsRxEnable = false,       // not using PRS input

    .prsRxCh = usartPrsRxCh0,   // doesn't matter what channel we select

  };

  USART_InitAsync(USART1, &uartInit);      // apply configuration to USART1

  USART1->ROUTE = USART_ROUTE_RXPEN | USART_ROUTE_TXPEN | _USART_ROUTE_LOCATION_LOC0; // clear buffers, enable transmitter and receiver pins

   

  USART_IntClear(USART1, _USART_IF_MASK);  // clear all USART interrupt flags

  NVIC_ClearPendingIRQ(USART1_RX_IRQn);    // clear pending RX interrupt flag in NVIC

  NVIC_ClearPendingIRQ(USART1_TX_IRQn);    // clear pending TX interrupt flag in NVIC

   

  USART_Enable(USART1, usartEnable);       // enable transmitter and receiver

   

  for(i=0; i<sizeof(test_string); i++) {

    while(!(USART1->STATUS & (1 << 6)));   // wait for TX buffer to empty

    USART1->TXDATA = test_string[i];       // send character

  }

     

  while(1) {

    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

      while(!(USART1->STATUS & (1 << 6))); // wait for TX buffer to empty

      USART1->TXDATA = rx_char;            // echo received char

      rx_char = 0;                         // clear temp variable

    }

  }

}