#include "stm32f4xx.h"

void USART2_Init(void) {
    GPIO_InitTypeDef GPIO_InitStructure;
    USART_InitTypeDef USART_InitStructure;

    /* 1. Enable Clocks */
    // GPIOA is on AHB1
    RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOA, ENABLE);
    // IMPORTANT: USART2 is on APB1 (unlike USART1 which is APB2)
    RCC_APB1PeriphClockCmd(RCC_APB1Periph_USART2, ENABLE);

    /* 2. Configure GPIO Pins (PA2 = TX, PA3 = RX) */
    GPIO_InitStructure.GPIO_Pin = GPIO_Pin_2 | GPIO_Pin_3;
    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF;      // Alternate Function
    GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
    GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;
    GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_UP;      // Pull-up is good for idle lines
    GPIO_Init(GPIOA, &GPIO_InitStructure);

    /* 3. Connect GPIO pins to Alternate Function 7 (USART2) */
    // This step is required for STM32F4!
    GPIO_PinAFConfig(GPIOA, GPIO_PinSource2, GPIO_AF_USART2); // PA2 -> USART2_TX
    GPIO_PinAFConfig(GPIOA, GPIO_PinSource3, GPIO_AF_USART2); // PA3 -> USART2_RX

    /* 4. Configure USART Parameters */
    USART_InitStructure.USART_BaudRate = 115200;
    USART_InitStructure.USART_WordLength = USART_WordLength_8b;
    USART_InitStructure.USART_StopBits = USART_StopBits_1;
    USART_InitStructure.USART_Parity = USART_Parity_No;
    USART_InitStructure.USART_HardwareFlowControl = USART_HardwareFlowControl_None;
    USART_InitStructure.USART_Mode = USART_Mode_Rx | USART_Mode_Tx;

    USART_Init(USART2, &USART_InitStructure);

    /* 5. Enable USART2 */
    USART_Cmd(USART2, ENABLE);
}

void USART2_SendChar(char ch) {
    // Wait until Transmit Data Register is Empty (TXE)
    while (USART_GetFlagStatus(USART2, USART_FLAG_TXE) == RESET);
    // Write data to register
    USART_SendData(USART2, (uint16_t)ch);
}

char USART2_ReadChar(void) {
    // Wait until Receive Data Register is Not Empty (RXNE)
    while (USART_GetFlagStatus(USART2, USART_FLAG_RXNE) == RESET);
    // Read data
    return (char)USART_ReceiveData(USART2);
}

int main(void) {
    // Initialize USART2
    USART2_Init();

    while (1) {
        /* ECHO LOGIC */
        
        // 1. Wait for a character to arrive and read it
        char received = USART2_ReadChar();
        
        // 2. Send the character back immediately
        USART2_SendChar(received);
        
        // Optional: If you press 'Enter' (CR), also send New Line (LF)
        if (received == '\r') {
            USART2_SendChar('\n');
        }
    }
}