#include "main.h"

I2C_HandleTypeDef hi2c1;

#define SLAVE_ADDR 0x3C << 1  // HAL expects 8-bit address (shifted left)
uint8_t txData[2];
uint8_t rxData[1];

void SystemClock_Config(void);
static void MX_GPIO_Init(void);
static void MX_I2C1_Init(void);

int main(void)
{
  HAL_Init();
  SystemClock_Config();
  MX_GPIO_Init();
  MX_I2C1_Init();

  while (1)
  {
    /*** Write data to a register ***/
    txData[0] = 0x00;   // Register address
    txData[1] = 0xAB;   // Data to write
    if (HAL_I2C_Master_Transmit(&hi2c1, SLAVE_ADDR, txData, 2, HAL_MAX_DELAY) == HAL_OK) {
      // Success
    } else {
      // Error
    }

    HAL_Delay(500);

    /*** Read data from a register ***/
    txData[0] = 0x01; // Register to read
    HAL_I2C_Master_Transmit(&hi2c1, SLAVE_ADDR, txData, 1, HAL_MAX_DELAY);
    if (HAL_I2C_Master_Receive(&hi2c1, SLAVE_ADDR, rxData, 1, HAL_MAX_DELAY) == HAL_OK) {
      // rxData[0] now contains the received byte
    } else {
      // Error
    }

    HAL_Delay(1000);
  }
}

/*** I2C1 Initialization ***/
static void MX_I2C1_Init(void)
{
  hi2c1.Instance = I2C1;
  hi2c1.Init.ClockSpeed = 100000;  // Standard mode 100kHz
  hi2c1.Init.DutyCycle = I2C_DUTYCYCLE_2;
  hi2c1.Init.OwnAddress1 = 0;
  hi2c1.Init.AddressingMode = I2C_ADDRESSINGMODE_7BIT;
  hi2c1.Init.DualAddressMode = I2C_DUALADDRESS_DISABLE;
  hi2c1.Init.OwnAddress2 = 0;
  hi2c1.Init.GeneralCallMode = I2C_GENERALCALL_DISABLE;
  hi2c1.Init.NoStretchMode = I2C_NOSTRETCH_DISABLE;
  if (HAL_I2C_Init(&hi2c1) != HAL_OK) {
    Error_Handler();
  }
}

/*** GPIO Init for I2C1 (PB6=SCL, PB7=SDA on Bluepill) ***/
static void MX_GPIO_Init(void)
{
  __HAL_RCC_GPIOB_CLK_ENABLE();
  GPIO_InitTypeDef GPIO_InitStruct = {0};

  GPIO_InitStruct.Pin = GPIO_PIN_6 | GPIO_PIN_7;
  GPIO_InitStruct.Mode = GPIO_MODE_AF_OD;
  GPIO_InitStruct.Pull = GPIO_PULLUP;
  GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_HIGH;
  GPIO_InitStruct.Alternate = GPIO_AF4_I2C1;
  HAL_GPIO_Init(GPIOB, &GPIO_InitStruct);
}