/* p4_6.c C library Console I/O using UART3 at 9600 Baud
 *
 * This program demonstrates the use of C library console I/O.
 * The functions _write() and _read() are implemented using
 * UART3Tx() and UART3Rx() for character I/O.
 * In the _read(), it always reads only a single character. The 
 * received character is echoed and if a '\r' is received,
 * it is substituted with a '\n' but both characters are echoed.
 * In _write() and _read(), 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 Atmel Studio 7 v7.0.1006
 */

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

void UART3_init(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 = 0;
    char str[80];

    UART3_init();

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

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

int _write(FILE *f, char *buf, int n) {
	int m = n;
	for (; n > 0; n--)
		UART3Tx(*buf++);
	return m;
}

int _read(FILE *f, char *buf, int n) {
	*buf = UART3Rx();
	if (*buf == '\r') {
		*buf = '\n';
		_write(f,"\r", 1);
	}
	_write(f, buf, 1);
	return 1;
}

int _close(FILE *f) {
	return 0;
}

int _fstat(FILE *f, void *p) {
	*((int*)p + 4) = 0x81b6; // enable read/write
	return 0;
}

int _isatty(FILE *f) {
	return 1;
}

int _lseek(FILE *f, int o, int w) {
	return 0;
}

void* _sbrk(int i) {
	return (void*)0x20006000;
}

/* _fstat() returns with permisson 666, that might not make a difference.
 * _sbrk() returns an address of RAM that might be free.
 * When scanf() is called, _read() gets a size of 400.
 * When prinft() is called, an extra '\n' at the end of format is required 
 * for some reason, otherwise the last char is truncated.
 */