Enthernet Code Comments - Answer Overflow

Enthernet Code

•Created by Sterling on 8/6/2024 in #firmware-and-baremetal

How to Receive Variable-Length Data Over RS485 Using HAL_UART_Receive_IT on STM32F4?

define the states for your state machine

typedef enum {
    RX_STATE_WAIT_FOR_HEADER,
    RX_STATE_WAIT_FOR_PAYLOAD
} RxState;

RxState rx_state = RX_STATE_WAIT_FOR_HEADER;

typedef enum {
    RX_STATE_WAIT_FOR_HEADER,
    RX_STATE_WAIT_FOR_PAYLOAD
} RxState;

RxState rx_state = RX_STATE_WAIT_FOR_HEADER;

define buffers and variables to store the received data

#define HEADER_SIZE

uint8_t uart_rx_header[HEADER_SIZE];
uint8_t uart_rx_payload[256];
uint8_t uart_rx_byte;
uint8_t byte_count = 0;

#define HEADER_SIZE

uint8_t uart_rx_header[HEADER_SIZE];
uint8_t uart_rx_payload[256];
uint8_t uart_rx_byte;
uint8_t byte_count = 0;

Initialize UART reception in the main function

HAL_UART_Receive_IT(&huart1, &uart_rx_byte, 1);

HAL_UART_Receive_IT(&huart1, &uart_rx_byte, 1);

Implement the HAL_UART_RxCpltCallback to handle the reception

void HAL_UART_RxCpltCallback(UART_HandleTypeDef *huart) {
    static uint8_t header_index = 0;
    static uint8_t payload_index = 0;

    if (huart->Instance == USART1) {
        switch (rx_state) {
            case RX_STATE_WAIT_FOR_HEADER:
                uart_rx_header[header_index++] = uart_rx_byte;

                if (header_index == HEADER_SIZE) {
                    byte_count = uart_rx_header[2];
                    rx_state = RX_STATE_WAIT_FOR_PAYLOAD;
                    header_index = 0;
                    payload_index = 0;

                    HAL_UART_Receive_IT(huart, uart_rx_payload, byte_count + 2);
                } else {
                    HAL_UART_Receive_IT(huart, &uart_rx_byte, 1);
                }
                break;

            case RX_STATE_WAIT_FOR_PAYLOAD;

                rx_state = RX_STATE_WAIT_FOR_HEADER;
                HAL_UART_Receive_IT(huart, &uart_rx_byte, 1);
                break;
        }
    }
}

void HAL_UART_RxCpltCallback(UART_HandleTypeDef *huart) {
    static uint8_t header_index = 0;
    static uint8_t payload_index = 0;

    if (huart->Instance == USART1) {
        switch (rx_state) {
            case RX_STATE_WAIT_FOR_HEADER:
                uart_rx_header[header_index++] = uart_rx_byte;

                if (header_index == HEADER_SIZE) {
                    byte_count = uart_rx_header[2];
                    rx_state = RX_STATE_WAIT_FOR_PAYLOAD;
                    header_index = 0;
                    payload_index = 0;

                    HAL_UART_Receive_IT(huart, uart_rx_payload, byte_count + 2);
                } else {
                    HAL_UART_Receive_IT(huart, &uart_rx_byte, 1);
                }
                break;

            case RX_STATE_WAIT_FOR_PAYLOAD;

                rx_state = RX_STATE_WAIT_FOR_HEADER;
                HAL_UART_Receive_IT(huart, &uart_rx_byte, 1);
                break;
        }
    }
}

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