CY8CKIT-041S-MAX 如何使用printf?

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

 * File Name:   main.c

 *

 * Description: This code avoids the usage of retarget-io and prints UART

 *              messages using printf() function.

 *

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



#include "cy_pdl.h"

#include "cybsp.h"



cy_stc_scb_uart_context_t CYBSP_DEBUG_UART_context;



void handle_error(void)

{

     /* Disable all interrupts. */

    __disable_irq();



    CY_ASSERT(0);

}



int main(void)

{

    cy_rslt_t result;

    cy_en_scb_uart_status_t initstatus;

    uint8_t read_data; /* Variable to store the received character

                        * through terminal */



    /* Initialize the device and board peripherals */

    result = cybsp_init();

    if (result != CY_RSLT_SUCCESS)

    {

        handle_error();

    }



    /* Enable global interrupts */

    __enable_irq();



    /* Initialize the UART */

    initstatus = Cy_SCB_UART_Init(CYBSP_DEBUG_UART_HW, &CYBSP_DEBUG_UART_config, &CYBSP_DEBUG_UART_context);



        /* Initialization failed. Handle error */

        if(initstatus!=CY_SCB_UART_SUCCESS)

        {

                handle_error();

        }



        /* Enable UART */

        Cy_SCB_UART_Enable(CYBSP_DEBUG_UART_HW);



        /* Transmit Header to the Terminal */

    printf("\x1b[2J\x1b[;H");

    printf("***********************************************************\r\n");

    printf("PSoC MCU UART Transmit and Receive\r\n");

    printf("***********************************************************\r\n\n");

    printf(">> Start typing to see the echo on the screen \r\n\n");



    for (;;)

    {



            /* Check if there is a received character from user console */

                if (0UL != Cy_SCB_UART_GetNumInRxFifo(CYBSP_DEBUG_UART_HW))

                {

                        /* Re-transmit whatever the user types on the console */

                        read_data = Cy_SCB_UART_Get(CYBSP_DEBUG_UART_HW);

                        printf("%c\r\n",read_data);



                }

    }

}



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

* When printf function is called it is redirected to the following functions

* depending on compiler used.

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

#if defined (__GNUC__)

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

* Function Name: _write

********************************************************************************

* Summary:

* NewLib C library is used to retarget printf to _write. printf is redirected to

* this function when GCC compiler is used to print data to terminal using UART.

*

* \param file

* This variable is not used.

* \param *ptr

* Pointer to the data which will be transfered through UART.

* \param len

* Length of the data to be transfered through UART.

*

* \return

* returns the number of characters transferred using UART.

* \ref int

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

   int _write(int file, char *ptr, int len)

    {

        /* Suppress the compiler warning about an unused variable. */

        if (0 != file)

        {

        }



        for(uint8_t i = 0; i