/* P9_1.c - I2C byte write to a DS1337
 *
 * This program initializes the 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.
 * No errors or acknowledgement are checked.
 *
 * The connections
 * I2C1_SCL - PB08
 * I2C1_SDA - PB09
 *
 * This program was tested with Keil uVision v5.24a with DFP v2.11.0
 */

#include "stm32f4xx.h"
#define SLAVE_ADDR 0x68    /* 1101 000.    DS1337 */

void delayMs(int n);

void I2C1_init(void);
int I2C1_byteWrite(char saddr, char maddr, char data);

int main(void)
{
    I2C1_init();

    I2C1_byteWrite(SLAVE_ADDR, 0x0E, 0);
 
    while(1)
    {
    }
}

void I2C1_init(void) {
    RCC->AHB1ENR |=  2;                     /* Enable GPIOB clock */
    RCC->APB1ENR |=  0x00200000;	        /* Enable I2C1 clock */

    /* configure PB8, PB9 pins for I2C1 */
    GPIOB->AFR[1]   &= ~0x000000FF;         /* PB8, PB9 I2C1 SCL, SDA */
    GPIOB->AFR[1]   |=  0x00000044;
    GPIOB->MODER    &= ~0x000F0000;         /* PB8, PB9 use alternate function */
    GPIOB->MODER    |=  0x000A0000;
    GPIOB->OTYPER   |=  0x00000300;         /* output open-drain */
    GPIOB->PUPDR    &= ~0x000F0000;         /* with pull-ups */
    GPIOB->PUPDR    |=  0x00050000;

    I2C1->CR1       =   0x8000;             /* software reset I2C1 */
    I2C1->CR1       &= ~0x8000;             /* out of reset */
    I2C1->CR2       =   0x0010;             /* peripheral clock is 16 MHz */
    I2C1->CCR       =   80;                 /* standard mode, 100kHz clock */
    I2C1->TRISE     =   17;                 /* maximum rise time */
    I2C1->CR1       |=  0x0001;             /* enable I2C1 module */
}

/* this funtion writes a byte 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_byteWrite(char saddr, char maddr, char data) {
    volatile int tmp;
    
    while (I2C1->SR2 & 2);                  /* wait until bus not busy */
    
    I2C1->CR1 |=  0x100;                    /* generate start */
    while (!(I2C1->SR1 & 1));               /* wait until start flag is set */
    
    I2C1->DR = saddr << 1;                  /* transmit slave address */
    while (!(I2C1->SR1 & 2));               /* wait until addr flag is set */
    tmp = I2C1->SR2;                        /* clear addr flag */
    
    while (!(I2C1->SR1 & 0x80));            /* wait until data register empty */
    I2C1->DR = maddr;                       /* send memory address */
    
    while (!(I2C1->SR1 & 0x80));            /* wait until data register empty */
    I2C1->DR = data;                        /* transmit data */
    
    while (!(I2C1->SR1 & 4));               /* wait until transfer finished */
    I2C1->CR1 |= 0x200;                     /* generate stop */

    return 0;
}