Harmony v3 Peripheral Libraries on SAMC2x: Step 5

Step 5: Add Application Code to the Project

The application is already developed and available in the main_c21n.c file under <your unzip folder>/samc21n_getting_started/dev_files/sam_c21n_xpro. The main_c21n.c file contains the application logic. It also contains placeholders that you will populate with necessary code in the next step.

  • Go to the samc21n_getting_started/dev_files/sam_c21n_xpro folder and copy the pre-developed main_c21n.c file.
  • Replace the main_c21n.c file of your project available at <Your project folder>/samc21n_getting_started/firmware/src by over-writing it with the copied file.
  • Open main_c21n.c in MPLAB® X IDE and add the application code by following the steps below:


Under the main_c21n.c file, in function main, notice the call to function SYS_Initialize. The generated function SYS_Initialize initializes all the peripheral modules used in the application (configured through MPLAB Harmony Configurator (MHC)).

Tip: Press the CTRL key and left click on the SYS_Initialize function. The click will open the implementation for the SYS_Initialize function as shown below.



In the main_c21n.c function, below SYS_Initialize(), add the following code to register callback event handlers.

SERCOM5_I2C_CallbackRegister(i2cEventHandler, 0);
DMAC_ChannelCallbackRegister(DMAC_CHANNEL_0, usartDmaChannelHandler, 0);
RTC_Timer32CallbackRegister(rtcEventHandler, 0);
EIC_CallbackRegister(EIC_PIN_3,EIC_User_Handler, 0);

Following the addition of the code above, add the function call.




The function call SERCOM5_I2C_CallbackRegister registers a callback event handler with the I²C Peripheral Library (PLIB). The event handler is called by the I²C PLIB when the I²C transfer is complete.


The function call DMAC_ChannelCallbackRegister registers a callback event handler with the Direct Memory Access (DMA) PLIB. The callback event handler is called by the DMA PLIB when the DMA transfer (of temperature sensor data to serial terminal) is complete.


The function call RTC_Timer32CallbackRegister registers an Real Time Clock (RTC) callback event handler with the RTC PLIB. The callback event handler is called by the RTC PLIB when the configured time period has elapsed.


The function call EIC_CallbackRegister registers an External Interrupt Controller (EIC) callback event handler with the EIC PLIB. The callback event handler is called by EIC PLIB when the user presses the switch SW0.


Implement the registered callback event handlers for RTC, I²C, Universal Synchronous Asynchronous Receiver Transmitter (USART), and EIC PLIBs by adding the following code before the main() function in main_c21n.c.

static void EIC_User_Handler(uintptr_t context)
    changeTempSamplingRate = true;      

static void rtcEventHandler (RTC_TIMER32_INT_MASK intCause, uintptr_t context)
    if (intCause & RTC_MODE0_INTENSET_CMP0_Msk)
        isRTCTimerExpired = true;                              

static void i2cEventHandler(uintptr_t contextHandle)
    if (SERCOM5_I2C_ErrorGet() == SERCOM_I2C_ERROR_NONE)
        isTemperatureRead = true;

static void usartDmaChannelHandler(DMAC_TRANSFER_EVENT event, uintptr_t contextHandle)
        isUSARTTxComplete = true;


Add the following code to submit an I²C transfer to read temperature sensor value when the configured time period (default 500 milliseconds) has elapsed. The I²C PLIB calls back the callback event handler (registered in Step 2 above) when the submitted request is complete.

isRTCTimerExpired = false;
SERCOM5_I2C_WriteRead(TEMP_SENSOR_SLAVE_ADDR, &i2cWrData, 1, i2cRdData, 2);


Add the following code to prepare the received temperature value from the sensor to be prepared on the serial terminal.

temperatureVal = getTemperature(i2cRdData);
sprintf((char*)uartTxBuffer, "Temperature = %02d F\r\n", temperatureVal);


Add the following code to implement the change of sampling rate and prepare a message for the same on the serial terminal when the user presses the switch SW0.

changeTempSamplingRate = false;
if(tempSampleRate == TEMP_SAMPLING_RATE_500MS)
    tempSampleRate = TEMP_SAMPLING_RATE_1S;
    sprintf((char*)uartTxBuffer, "Sampling Temperature every 1 second \r\n");
else if(tempSampleRate == TEMP_SAMPLING_RATE_1S)
    tempSampleRate = TEMP_SAMPLING_RATE_2S;
    sprintf((char*)uartTxBuffer, "Sampling Temperature every 2 seconds \r\n");        
else if(tempSampleRate == TEMP_SAMPLING_RATE_2S)
    tempSampleRate = TEMP_SAMPLING_RATE_4S;
    sprintf((char*)uartTxBuffer, "Sampling Temperature every 4 seconds \r\n");        
else if(tempSampleRate == TEMP_SAMPLING_RATE_4S)
   tempSampleRate = TEMP_SAMPLING_RATE_500MS;
   sprintf((char*)uartTxBuffer, "Sampling Temperature every 500 ms \r\n");        


Add code to transfer the buffer containing either:

  • the latest temperature value in the format “Temperature = XX F\r\n”, over or
  • the message mentioning the change of sampling rate over USART using DMA.
DMAC_ChannelTransfer(DMAC_CHANNEL_0, uartTxBuffer, (const void *)&(SERCOM4_REGS->USART_INT.SERCOM_DATA), strlen((const char*)uartTxBuffer));

You are now ready to build the code!

Next Step >

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