5.2.2.1 Application Logic

To develop and run the application, follow these steps:

1. Open the main.c file of the project located in the source files folder. Add the following code outside the main() function:

   #define RX_BUFFER_SIZE 1
   bool USART1_writeStatus = false;
   bool USART1_readStatus = false;
   
   bool USART0_writeStatus = false;
   bool USART0_readStatus = false;
   
   void USART1_WriteEventHandler ( uintptr_t context )
   {
       USART1_writeStatus = true;
   }
   
   void USART0_WriteEventHandler ( uintptr_t context )
   {
       USART0_writeStatus = true;
   }
   
   void USART1_ReadEventHandler (uintptr_t context)
   {
       USART1_readStatus = true;
   }
   
   void USART0_ReadEventHandler (uintptr_t context)
   {
       USART0_readStatus = true;
   } 
   

2. In the following figure, the read and write event handlers are declared same as the callback registers seen in the SAM D21 Curiosity Nano Evaluation Kit.

   

3. Add the following code inside the main() function:

   /* Initialize all modules */
       SYS_Initialize ( NULL );
       
       // EDBG SERCOM Read and Write Callback
       USART1_WriteCallbackRegister(USART1_WriteEventHandler, (uintptr_t)NULL);
       USART1_ReadCallbackRegister(USART1_ReadEventHandler, (uintptr_t)NULL);
       
       // Extension SERCOM Read and Write Callback
       USART0_WriteCallbackRegister(USART0_WriteEventHandler, (uintptr_t)NULL);
       USART0_ReadCallbackRegister(USART0_ReadEventHandler, (uintptr_t)NULL);
       
       uint8_t rxBuffer; 
   

4. In the following code examples, SYS_Initialize (NULL) initializes the modules like clock, Nested Vector Interrupt Controller (NVIC), Embedded Flash Controller (EFC), Parallel In/Out Controller (PIO), and USART. Also, the callback register functions for read and write operations are declared.

   

5. Add the following code after the initialization of modules:

   // Read request for EDBG
       USART1_Read(&rxBuffer, RX_BUFFER_SIZE);
       
   // Read request for Extension
       USART0_Read(&rxBuffer, RX_BUFFER_SIZE); 
   

6. Start the implementation with a read request for USART0 (for Extension) and USART1 (for EDBG).

   

7. Add the following code inside the while loop:

   if(USART0_readStatus == true)
           {
               USART0_readStatus = false;
               
               //Transmit received bytes from EDBG
               USART1_Write(&rxBuffer, RX_BUFFER_SIZE);
           }
           
           if(USART1_writeStatus == true)
           {
               USART1_writeStatus = false;
               USART0_Read(&rxBuffer, RX_BUFFER_SIZE);
           }
           
           if(USART1_readStatus == true)
           {
               USART1_readStatus = false;
               //Transmit received bytes from Extension
               USART0_Write(&rxBuffer, RX_BUFFER_SIZE);
           }
           if(USART0_writeStatus == true)
           {
               USART0_writeStatus = false;
               USART1_Read(&rxBuffer, RX_BUFFER_SIZE);
           } 
   

8. In the following figure, if the Extension is ready to read (Rx) the data (i.e., USART0_readStatus == true), then it transmits the received data to EDBG, and if the Extension is ready to write (Tx) the data (i.e., USART1_writeStatus == true), then EDBG will start a read (Rx) request. Similarly, vice versa if the EDBG is ready to read (Rx) or if the EDBG is ready to write (Tx).