/* P9_3.c - I2C burst write to a DS3231
 *
 * This program initializes the I2C and write the
 * initialization data to a DS3231.
 * No errors or acknowledgement are checked.
 *
 * The connections
 * I2C1_SCL - PB8
 * I2C1_SDA - PB9
 *
 * This program was tested with Keil uVision v5.23 with DFP v2.0.0
 */

#include "stm32f0xx.h"
#define SLAVE_ADDR 0x68    /* 1101 000.    DS3231 */

void delayMs(int n);

void I2C1_init(void);
int I2C1_burstWrite(char saddr, char maddr, int n, char* data);

int Main(void)
{
    /*                          00    01    02    03    04    05    06 */
    char timeDateToSet[15] = {0x55, 0x58, 0x10, 0x03, 0x26, 0x09, 0x17, 0};
                                /* 2017 September 26, Tuesday, 10:58:55 */
    I2C1_init();
    I2C1_burstWrite(SLAVE_ADDR, 0, 7, timeDateToSet);

    while (1) {
    }
}

void I2C1_init(void) {
    RCC->AHBENR  |=  0x00040000;		/* Enable GPIOB clock */
    RCC->APB1ENR |=  0x00200000;		/* Enable I2C1 clock */

    /* configure PB8, PB9 pins for I2C1 */
    GPIOB->MODER    &= ~0x000F0000;     /* PB8, PB9 use alternate function */
    GPIOB->MODER    |=  0x000A0000;
    GPIOB->AFR[1]   &= ~0x000000FF;     /* PB8, PB9 I2C1 SCL, SDA */
    GPIOB->AFR[1]   |=  0x00000011;
    GPIOB->OTYPER   |=  0x00000300;     /* output open-drain */
    GPIOB->PUPDR    &= ~0x000F0000;     /* with pull-ups */
    GPIOB->PUPDR    |=  0x00050000;

    I2C1->CR1       = 0;                /* software reset I2C1 */
    I2C1->TIMINGR   = 0x10420F13;       /* 100 KHz, peripheral clock is 8 MHz */
    I2C1->CR1       = 0x00000001;       /* enable I2C1 module */
}

/* this function writes multiple bytes of data to the memory location maddr of
 * a device with I2C slave device address saddr.
 * For simplicity, no error checking or error report is done.
 */
int I2C1_burstWrite(char saddr, char maddr, int n, char* data) {
    int i;

    while (I2C1->ISR & 0x8000);             /* wait until bus not busy */

    I2C1->CR2 = 0x02002000 |            /* generate start, set byte count, */
        ((n + 1)<< 16) | (saddr << 1);  /* set auto end, and send slave address */

    while (!(I2C1->ISR & 0x02));            /* wait until TXIS is set */
    I2C1->TXDR = maddr;                     /* send memory address */

    for (i = 0; i < n; i++)                 /* send n bytes of data */
    {
        while (!(I2C1->ISR & 0x02));        /* wait until TXIS is set */
        I2C1->TXDR = *data++;               /* send a byte of data */
    }

    while (!(I2C1->ISR & 0x20));            /* wait until stop flag is set */

    I2C1->ICR = 0x20;                       /* clear stop flag */
    I2C1->CR2 = 0x02000000;                 /* clear configuration register 2 */

    return 0;
}