/* P9_2.c - Test I2C byte read with DS1337
 *
 * This program initializes the SERCOM1 as I2C and continuously
 * reads the register 0 of the DS1337.
 * Register 0 contains the second count. The clock is powered-up
 * enabled and the second count is incrementing. The bit 0 is 
 * used to turn on and off the LED0 of the SAMD21 Xplained Pro
 * board. The LED0 should blink every second.
 * PA16 = SDA, PA17 = SCL
 * No errors or acknowledgement are checked.
 *
 * Tested with Atmel Studio 7 v7.0.1006 and Keil MDK-ARM v5.21a.
 */

#include "samd21.h"

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

#define SLAVE_ADDR 0x68     /* 1101 000.    DS1337 */

void I2C2_init(void) ;
int I2C2_byte_write(unsigned char saddr, unsigned char maddr, unsigned char data);
int I2C2_byte_read(unsigned char saddr, unsigned char maddr, unsigned char* data);
void delayMs(int n);

int main (void) {
    unsigned char data;
    
    I2C2_init();
    REG_PORT_DIRSET1 = 0x40000000;       /* make PB30 output */

    while (1) {
        I2C2_byte_read(SLAVE_ADDR, 0, &data);
        if (data & 1)
            REG_PORT_OUTCLR1 = 0x40000000;  /* turn on LED0 */
        else
            REG_PORT_OUTSET1 = 0x40000000;  /* turn off LED0 */
        
        delayMs(10);
    }
}

void I2C2_init(void) {
    REG_PM_APBCMASK |= 0x00000008;          /* SERCOM1 bus clock */
    GCLK->CLKCTRL.reg = 0x4015;             /* SERCOM1 core clock */

    ARRAY_PORT_PINCFG0[16] |= 1;            /* allow pmux to set PA16 pin configuration */
    ARRAY_PORT_PINCFG0[17] |= 1;            /* allow pmux to set PA17 pin configuration */
    ARRAY_PORT_PMUX0[8] = 0x22;             /* PA16 = SDA, PA17 = SCL */

    REG_SERCOM1_I2CM_CTRLA = 1;             /* reset SERCOM1 */
    while (REG_SERCOM1_I2CM_CTRLA & 1) {}   /* wait for reset to complete */
    REG_SERCOM1_I2CM_CTRLA = 0x14;          /* master mode */
    REG_SERCOM1_I2CM_BAUD = 0;              /* 1MHz main clock -> ~100KHz I2C clock */
    REG_SERCOM1_I2CM_CTRLA |= 2;            /* enable SERCOM1 */
    REG_SERCOM1_I2CM_STATUS = 0x10;         /* force idle */
}

int I2C2_byte_read(unsigned char saddr, unsigned char maddr, unsigned char* data) {
    while((REG_SERCOM1_I2CM_STATUS & 0x30) != 0x10) ; /* wait until idle */

    REG_SERCOM1_I2CM_ADDR = saddr << 1;         /* send slave address */
    while((REG_SERCOM1_I2CM_INTFLAG & 1) == 0); /* wait until saddr sent */

    REG_SERCOM1_I2CM_DATA = maddr;              /* send memory address */
    while((REG_SERCOM1_I2CM_INTFLAG & 1) == 0); /* wait until maddr sent */

    REG_SERCOM1_I2CM_ADDR = (saddr << 1) | 1;   /* send restart with slave address */
    while((REG_SERCOM1_I2CM_INTFLAG & 2) == 0); /* wait until data received */

    *data = REG_SERCOM1_I2CM_DATA;              /* read data */

    REG_SERCOM1_I2CM_CTRLB |= 0x40000;          /* generate nack */
    REG_SERCOM1_I2CM_CTRLB |= 0x30000;          /* issue a stop */
    return 0;
}

// delay n milliseconds (1MHz CPU clock)
void delayMs(int n) {
    int i;
	for (; n > 0; n--)
		for (i = 0; i < 199; i++)
			__asm("nop");
}