#include <stm32f1xx.h>		//Core Header for STM32F103C8T6 Processor
#include <stdio.h>

#define EEPROM_DEVICE 0xA0 //All Addresspins grounded
#define EEPROM_WRITE  0
#define EEPROM_READ	  1

int main(void) {

	//Enable Clocks
	RCC->APB2ENR |= RCC_APB2ENR_IOPBEN;							//Enable Clock for I/O Modul B (GPIOB)
	RCC->APB2ENR |= RCC_APB2ENR_AFIOEN;							//Enable Clock for Alternate Function (AF)
	RCC->APB1ENR |= RCC_APB1ENR_I2C1EN;							//Enable Clock for I2C1 Modul
	
	//Init I2C at 100KHz APB1=36MHz
	I2C1->CR1 &= ~(I2C_CR1_SWRST | I2C_CR1_SMBUS | I2C_CR1_PE);	//No Software Reset and No SMBus Mode and disable I2C Bus
	I2C1->CR2 |= 36;											//Set I2C Peripheral Clock to APB1 Bus Clock(36MHz)

	I2C1->CCR &= ~(I2C_CCR_FS);									//Standard Mode selected
	I2C1->CCR |= 180;											//Set Clock Generator 100 KHz
	I2C1->TRISE = 37;											//Set Trise for SCL

	I2C1->CR1 |= I2C_CR1_ACK | I2C_CR1_PE;						//Enable I2C Bus and ACK Generation

	//Configurate PB6/PB7 for SDA/SCL as Open Drain Alternate Function
	GPIOB->CRL |= GPIO_CRL_MODE6_1 | GPIO_CRL_CNF6;				//Set PB6 to Output Mode Max 2 MHz Alternate Function Open drain
	GPIOB->CRL |= GPIO_CRL_MODE7_1 | GPIO_CRL_CNF7; 			//Set PB7 to Output Mode Max 2 MHz Altenrate Function Open drain
	GPIOB->CRL &= ~(GPIO_CRL_MODE6_0 | GPIO_CRL_MODE7_0);	
	
	//Write 0x20 at Address 0x08 to EEPROM Chip
	
	//Step 1 generate Start and send device Address
	while(I2C1->SR2 & I2C_SR2_BUSY);							//Check if I2C Bus is not Busy
	I2C1->CR1 |= I2C_CR1_ACK | I2C_CR1_START;					//Enable ACK Generation and generate START Condition
	while(!(I2C1->SR1 & I2C_SR1_SB));							//Wait for START Condition been generated
	I2C1->DR = EEPROM_DEVICE + EEPROM_WRITE;					//Set the EEPROM Address with Write Command
	while(!(I2C1->SR1 & I2C_SR1_ADDR));							//Wait for Address Match
	
	(void)I2C1->SR2;											//Dummy Read to clear Flags. SR1 is already cleared during the while loop
	
	//Step 2 send Data
	//Send EEPROM Memory Address
	while(!(I2C1->SR1 & I2C_SR1_TXE));							//Check if TX Buffer is empty
	I2C1->DR = 0x08;											//Set Internal EEPROM Memory Address
	while(!(I2C1->SR1 & I2C_SR1_BTF));							//Wait until Byte is send
	
	//Send Data to store in EEPROM
	while(!(I2C1->SR1 & I2C_SR1_TXE));							//Check if TX Buffer is empty
	I2C1->DR = 0x20;											//Send Data
	while(!(I2C1->SR1 & I2C_SR1_BTF));							//Wait until Byte is send
	
	//Step 3 generate Stop Condition
	I2C1->CR1 |= I2C_CR1_STOP;									//Generate STOP Condition
	
	while(1) {
		
	}
}