/* p4_5.c C library Console I/O using UART3 at 9600 Baud
 *
 * This program demonstrates the use of C library console I/O.
 * The functions fputc() and fgetc() are implemented using
 * UART3Tx() and UART3Rx() for character I/O.
 * In the fgetc(), the received character is echoed and if a '\r'
 * is received, it is substituted with a '\n' but both characters are
 * echoed.
 * In fputc() and fgetc(), the file descripter is not checked. All
 * file I/O's are directed to the console.
 *
 * By default, the clock is running at 1 MHz.
 *
 * Tested with Keil MDK-ARM v5.20 Device Family Pack v1.2.0.
 */

#include "samd21.h"
#include <stdio.h>

void UART3_init(void);
unsigned char UART3Rx(void);
int UART3Tx(unsigned char c);

unsigned char* ARRAY_PORT_PINCFG0 = (unsigned char*)&REG_PORT_PINCFG0;
unsigned char* ARRAY_PORT_PMUX0 = (unsigned char*)&REG_PORT_PMUX0;

int main(void) {
    int n;
    char str[80];

    UART3_init();

    printf("Test stdio library console I/O functions\r\n");
    fprintf(stdout, "    test for stdout\r\n");
    fprintf(stderr, "    test for stderr\r\n");

    while (1) {
        printf("please enter a number: ");
        scanf("%d", &n);
        printf("the number entered is: %d\r\n", n);
        printf("please type a string: ");
        gets(str);
        printf("the string entered is: ");
        puts(str);
        printf("\r\n");
    }
}

/* initialize UART3 to 9600 Baud at 1 MHz core clock */
void UART3_init(void) {
    REG_PM_APBCMASK |= 0x00000020;  /* enable bus clock for SERCOM3 */
    REG_GCLK_CLKCTRL = 0x4017;      /* GCLK0 to SERCOM3 */

    REG_SERCOM3_USART_CTRLA |= 1;               /* reset SERCOM3 */
    while (REG_SERCOM3_USART_SYNCBUSY & 1) {}   /* wait for reset to complete */
    REG_SERCOM3_USART_CTRLA = 0x40106004;       /* LSB first, async, no parity,
        PAD[0]-TxD, PAD[1]-RxD BAUD uses fraction, 8x oversampling, internal clock */
    REG_SERCOM3_USART_CTRLB = 0x00030000;       /* enable Tx/Rx, one stop bit, 8 bit */
    REG_SERCOM3_USART_BAUD  = 13;               /* 1000000/8/9600 = 13.02 */
    REG_SERCOM3_USART_CTRLA |= 2;               /* enable SERCOM3 */
    while (REG_SERCOM3_USART_SYNCBUSY & 2) {}   /* wait for enable to complete */
        
    ARRAY_PORT_PINCFG0[22] |= 1;    /* allow pmux to set PA22 pin configuration */
    ARRAY_PORT_PINCFG0[23] |= 1;    /* allow pmux to set PA23 pin configuration */
    ARRAY_PORT_PMUX0[11] = 0x22;    /* PA22 = TxD, PA23 = RxD */
}

/* read a character from UART3 */
unsigned char UART3Rx(void) {
    char c;

    while(!(REG_SERCOM3_USART_INTFLAG & 4)) {}  /* wait until receive complete */
    c = REG_SERCOM3_USART_DATA;                 /* read the receive char */
    return c;
}

/* write a character to UART */
int UART3Tx(unsigned char c) {
    while(!(REG_SERCOM3_USART_INTFLAG & 1)) {}  /* wait for data register empty */
    REG_SERCOM3_USART_DATA = c;                 /* send a char */
    return c;
}

/* The code below is the interface to the C standard I/O library.
 * All the I/O are directed to the console, which is UART3.
 */
struct __FILE { int handle; };
FILE __stdin  = {0};
FILE __stdout = {1};
FILE __stderr = {2};

/* Called by C library console/file input
 * This function echoes the character received.
 * If the character is '\r', it is substituted by '\n'.
 */
int fgetc(FILE *f) {
    int c;

    c = UART3Rx();      /* read the character from console */

    if (c == '\r') {    /* if '\r', replace with '\n' */
        UART3Tx(c);     /* echo */
        c = '\n';
    }

    UART3Tx(c);         /* echo */

    return c;
}

/* Called by C library console/file output */
int fputc(int c, FILE *f) {
    return UART3Tx(c);  /* write the character to console */
}