3.17.20 Universal Asynchronous Receiver Transmitter (UART)

Using The Library

Blocking Mode

#define RX_BUFFER_SIZE 10
char message[] = "UART Example in blocking mode";
char receiveBuffer[RX_BUFFER_SIZE] = {0};
UART_ERROR errorStatus;
char rxData = 0;

int main ( void )
{    
    /* Initialize all modules */
    SYS_Initialize ( NULL );

    /* Transmit buffer*/
    UART1_Write(message, sizeof(message));
	
	/* Wait for a character to be received */
	while(UART1_ReceiverIsReady() == false);
		
	if(UART1_ErrorGet() == UART_ERROR_NONE)
	{
		/* Read a byte */
		rxData = UART1_ReadByte();
	}
	
	/* Receive buffer */
    if (UART1_Read(receiveBuffer, RX_BUFFER_SIZE)) == false)
	{
		/* Read failed, get the error */
		errorStatus UART1_ErrorGet();
		
		/* Handle the error */
	}
    else
	{
		/* Transmit the received buffer*/
		UART1_Write(receiveBuffer, RX_BUFFER_SIZE);
	}

	...

    /* Execution should not come here during normal operation */

    return ( EXIT_FAILURE );
}

Non-blocking Mode

#define RX_BUFFER_SIZE 10

char message[] = "**** Non-blocking Transfer with the interrupt  ****\r\n\
**** Type 10 characters. The received characters are echoed back ****\r\n";

char messageError[] = "**** UART error occurred ****\r\n";

char receiveBuffer[RX_BUFFER_SIZE] = {0};
char echoBuffer[RX_BUFFER_SIZE+4] = {0};

bool errorStatus = false;
bool writeStatus = false;
bool readStatus = false;

void APP_WriteCallback(uintptr_t context)
{
    writeStatus = true;
}

void APP_ReadCallback(uintptr_t context)
{
    if(UART1_ErrorGet() != UART_ERROR_NONE)
    {
        /* ErrorGet clears errors, set error flag to notify console */
        errorStatus = true;
    }
    else
    {
        readStatus = true;
    }
}

int main ( void )
{
    /* Initialize all modules */
    SYS_Initialize ( NULL );

    /* Register callback functions and send start message */
    UART1_WriteCallbackRegister(APP_WriteCallback, 0);
    UART1_ReadCallbackRegister(APP_ReadCallback, 0);
    UART1_Write(&message[0], sizeof(message));

    while ( true )
    {
        if(errorStatus == true)
        {
            /* Send error message to console */
            errorStatus = false;
            UART1_Write(&messageError[0], sizeof(messageError));
        }
        else if(readStatus == true)
        {
            /* Echo back received buffer and Toggle LED */
            readStatus = false;

            echoBuffer[0] = '\n';
            echoBuffer[1] = '\r';
            memcpy(&echoBuffer[2], receiveBuffer,sizeof(receiveBuffer));
            echoBuffer[RX_BUFFER_SIZE+2] = '\n';
            echoBuffer[RX_BUFFER_SIZE+3] = '\r';

            UART1_Write(&echoBuffer[0], sizeof(echoBuffer));
        }
        else if(writeStatus == true)
        {
            /* Submit buffer to read user data */
            writeStatus = false;
            UART1_Read(&receiveBuffer[0], sizeof(receiveBuffer));
        }
        else
        {
            /* Repeat the loop */
            ;
        }
    }

    /* Execution should not come here during normal operation */

    return ( EXIT_FAILURE );
}

Ring buffer Mode

uint8_t txBuffer[50];
uint8_t rxBuffer[10];
volatile uint32_t nBytesRead = 0;
volatile bool txThresholdEventReceived = false;
volatile bool rxThresholdEventReceived = false;

void UARTReadEventHandler(UART_EVENT event, uintptr_t context )
{
    uint32_t nBytesAvailable = 0;
    
    if (event == UART_EVENT_READ_THRESHOLD_REACHED)
    {
        /* Receiver should atleast have the thershold number of bytes in the ring buffer */
        nBytesAvailable = UART1_ReadCountGet();
        
        nBytesRead += UART1_Read((uint8_t*)&rxBuffer[nBytesRead], nBytesAvailable);                          
    }
}

void UARTWriteEventHandler(UART_EVENT event, uintptr_t context )
{
    txThresholdEventReceived = true;
}

int main ( void )
{
    uint32_t nBytes = 0;        
    
    /* Initialize all modules */
    SYS_Initialize ( NULL );          
    
    /* Register a callback for write events */
    UART1_WriteCallbackRegister(UARTWriteEventHandler, (uintptr_t) NULL);
    
    /* Register a callback for read events */
    UART1_ReadCallbackRegister(UARTReadEventHandler, (uintptr_t) NULL);              
    
    /* Print the size of the read buffer on the terminal */
    nBytes = sprintf((char*)txBuffer, "RX Buffer Size = %d\r\n", (int)UART1_ReadBufferSizeGet());
    
    UART1_Write((uint8_t*)txBuffer, nBytes);  
    
    /* Print the size of the write buffer on the terminal */
    nBytes = sprintf((char*)txBuffer, "TX Buffer Size = %d\r\n", (int)UART1_WriteBufferSizeGet());
    
    UART1_Write((uint8_t*)txBuffer, nBytes);    
    
    UART1_Write((uint8_t*)"Adding 10 characters to the TX buffer - ", sizeof("Adding 10 characters to the TX buffer - "));    
    
    /* Wait for all bytes to be transmitted out */
    while (UART1_WriteCountGet() != 0);    
    
    UART1_Write((uint8_t*)"0123456789", 10);           
        
    /* Print the amount of free space available in the TX buffer. This should be 10 bytes less than the configured write buffer size. */
    nBytes = sprintf((char*)txBuffer, "\r\nFree Space in Transmit Buffer = %d\r\n", (int)UART1_WriteFreeBufferCountGet());

    UART1_Write((uint8_t*)txBuffer, nBytes);    
    
    /* Let's enable notifications to get notified when the TX buffer is empty */
    UART1_WriteThresholdSet(UART1_WriteBufferSizeGet());   
    
    /* Enable notifications */
    UART1_WriteNotificationEnable(true, false);
   
    /* Wait for the TX buffer to become empty. Flag "txThresholdEventReceived" is set in the callback. */
    while (txThresholdEventReceived == false);
    
    txThresholdEventReceived = false;    
    
    /* Disable TX notifications */
    UART1_WriteNotificationEnable(false, false);
    
    UART1_Write((uint8_t*)"Enter 10 characters. The received characters are echoed back. \r\n>", sizeof("Enter 10 characters. The received characters are echoed back. \r\n>"));               
            
    /* Wait till 10 (or more) characters are received */
    while (UART1_ReadCountGet() < 10);
    
    /* At-least 10 characters are available in the RX buffer. Read out into the application buffer */
    UART1_Read((uint8_t*)rxBuffer, 10);  
    
    /* Echo the received data */
    UART1_Write((uint8_t*)rxBuffer, 10);    
    
    /* Now demonstrating receiver notifications */
    UART1_Write((uint8_t*)"\r\n Now turning on RX notifications \r\n>", sizeof("\r\n Now turning on RX notifications \r\n>"));
    
    /* For demonstration purpose, set a threshold value to receive a callback after every 5 characters are received */
    UART1_ReadThresholdSet(5);
    
    /* Enable RX event notifications */
    UART1_ReadNotificationEnable(true, false);
                   
    while(1)
    {
        /* Wait until at-least 10 characters are entered by the user */
        while (nBytesRead < 10);    
    
        /* Echo the received data */
        UART1_Write((uint8_t*)rxBuffer, nBytesRead);
        
        UART1_Write((uint8_t*)"\r\n>", 3);

        nBytesRead = 0;
    }

    /* Execution should not come here during normal operation */

    return ( EXIT_FAILURE );
}

Library Interface

UART peripheral library provides the following interfaces:

Functions

Data types and constants