/* P9_1.c - Test I2C byte write with DS1337
 *
 * This program initializes the SERCOM1 as I2C and sends a
 * command to the DS1337 to turn on the 1 Hz output.
 * 1 Hz output is an open-drain output. It needs a pull-up
 * to observe the signal.
 * 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 I2C_init(void) ;
int I2C_byte_write(unsigned char saddr, unsigned char maddr, unsigned char data);

int main (void) {
    I2C_init();
    I2C_byte_write(SLAVE_ADDR, 0x0E, 0);    /* write 0 to location 0x0E */
    
    while (1) {
    }
}

void I2C_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 I2C_byte_write(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 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_DATA = data;               /* send data */
    while((REG_SERCOM1_I2CM_INTFLAG & 1) == 0); /* wait until data sent */

    REG_SERCOM1_I2CM_CTRLB |= 0x30000;          /* issue a stop */

    return 0;
}