UART Drivers

The Embedded SDK includes a UART driver for the microcontrollers that contain a UART peripheral. The UART drivers are provided with a common public API so that they can be used across any of the supported platforms. The UART drivers do not preallocate any memory or other resources; therefore unused ports will not use any resources unless explicitly opened by the application.

Opening A Port

The code snippet below demonstrates how to initialize the driver and open a UART port.

#include "mcu_uart.h"
#include <assert.h>

static UART uart;                           /* Allocate an instance of the driver */

void APP_Function(void)
{
    STATUS status;


    status = UART_Open(&uart,               /* Open a UART */		 
                       0,                   /* Port number (0 in this case) */
                       115200,              /* Baud rate, in bits per second */
                       8,                   /* Number of data bits */
                       STOPBITS_ONE,        /* Number of stop bits */
                       PARITY_NONE,         /* Parity option */
                       HANDSHAKE_NONE);     /* Handshake option */

    assert(status == SUCCESS);
}

Transferring Data

The UART drivers utilize circular buffers that are provided by the kernel for maintaining data while either an interrupt or DMA can complete the actual transfers. The UART driver will automatically place received data into its underlying receive buffer. Use UART_Read() to retrieve data from the receive buffer.

The snippet below demonstrates how to receive and echo data over a UART.

void APP_Function(void)
{
    STATUS status;
    UINT32 actual;
    BYTE buf[32];


    status = UART_Read(&uart,                   /* Retrieve data from the UART */
                       buf,                     /* Pointer to a buffer to receive the data */
                       sizeof(buf),             /* The size, in bytes, of the buffer */
                       &actual,                 /* A pointer to variable to get actual amount */
                       10);                     /* Max time to wait, in kernel ticks */

    if (status == SUCCESS) {                    /* Any error occur? */
        if (actual > 0) {                       /* Any data received? */

            /* actual = the number of bytes
            that have been returned in
            the buffer 'buf' */

            status = UART_Write(&uart,          /* Write the received data out (echo) */
                                buf,            /* Pointer to the data to write */
                                actual,         /* Number of bytes to write */
                                NULL,           /* Pointer to variable for actual bytes written */
                                1000);          /* Max time to wait to complete, in kernel ticks */

            assert(status == SUCCESS);
        }
    }
}

Configuration

The size of the underlying buffers used by the UART driver can be configured within the mcu_cfg.h header file. The snippet below shows the configuration items for adjusting the UART buffer sizes.

/*******************************************************************************************************************************************

    UART RX BUFFER SIZE             The size, in bytes, of the buffer used for receiving data from a UART.

*******************************************************************************************************************************************/
#define CFG_UARTRXBUFFERSIZE        128

/*******************************************************************************************************************************************

    UART TX BUFFER SIZE             The size, in bytes, of the buffer used for transmitting data to a UART.

*******************************************************************************************************************************************/
#define CFG_UARTTXBUFFERSIZE        128