I2C @ STM32L476RG

void config_i2c(void) {

  //Initialize PB13 and PB14 as SCL and SDA respectively:

  {

    RCC->AHB2ENR |= RCC_AHB2ENR_GPIOBEN;

    //Configure PB13 as SCL:

    {

      GPIOB->AFR[1] &= ~(GPIO_AFRH_AFRH5);

      GPIOB->AFR[1] |= ((uint32_t)GPIO_AF4_I2C2) << GPIO_AFRH_AFSEL13_Pos;

      GPIOB->MODER |= GPIO_MODER_MODER13_1;

      GPIOB->OTYPER |= GPIO_OTYPER_OT13;

      GPIOB->OSPEEDR |= GPIO_OSPEEDER_OSPEEDR13;

    }

    //Configure PB14 as SDA:

    {

      GPIOB->AFR[1] &= ~(GPIO_AFRH_AFRH6);

      GPIOB->AFR[1] |= ((uint32_t)GPIO_AF4_I2C2) << GPIO_AFRH_AFSEL14_Pos;

      GPIOB->MODER |= GPIO_MODER_MODER14_1;

      GPIOB->OTYPER |= GPIO_OTYPER_OT14;

      GPIOB->OSPEEDR |= GPIO_OSPEEDER_OSPEEDR14;

    }

  }

  //Initialize the I2C interface for master mode:

  {

    //Make sure HSI16 clock is turned on.

    RCC->CR |= RCC_CR_HSION;

    while(!(RCC->CR & RCC_CR_HSIRDY));

    //Select HSI16 clock as I2C2 clock.

    RCC->CCIPR |= RCC_CCIPR_I2C2SEL_1;

    //Enable the clock for the I2C interface.

    RCC->APB1ENR1 |= RCC_APB1ENR1_I2C2EN;

    //Disable the I2C peripheral.

    I2C2->CR1 &= ~(I2C_CR1_PE);

    //Configure timing for "Fast-mode".

    //(See Table 236 of the Reference Manual "RM0351, Rev 9" for the values.)

    I2C2->TIMINGR =

      (0x1u << I2C_TIMINGR_PRESC_Pos) +

      (0x9u << I2C_TIMINGR_SCLL_Pos) +

      (0x3u << I2C_TIMINGR_SCLH_Pos) +

      (0x2u << I2C_TIMINGR_SDADEL_Pos) +

      (0x3u << I2C_TIMINGR_SCLDEL_Pos);

    //"Stop" and "Restart" will be generated by software.

    I2C2->CR2 &= ~(I2C_CR2_AUTOEND);

    //Configure 7-bit addressing and set slave address.

    I2C2->CR2 &= ~(I2C_CR2_ADD10);

    I2C2->CR2 &= ~(I2C_CR2_SADD);

    I2C2->CR2 |= (NV_RAM_DEVICE_ADDRESS << 1)&0xFEul;

    //Enable the I2C peripheral.

    I2C2->CR1 |= I2C_CR1_PE;

  }

}

void do_some_magic(void) {

  //Set transfer dir. "write".

  I2C2->CR2 &= ~(I2C_CR2_RD_WRN);

  //Configure number of bytes to be written.

  I2C2->CR2 |= 1 << I2C_CR2_NBYTES_Pos;

  //Generate "Start Condition".

  I2C2->CR2 |= I2C_CR2_START;

  while(I2C2->CR2&I2C_CR2_START); //<-- HIER DREHT ES "FOREVER"

  return;

}