XMODEM Library for STM32 (HAL-Based)

This repository provides a lightweight implementation of the XMODEM file transfer protocol for STM32 microcontrollers using the STM32 HAL library.
It supports both transmit and receive operations over UART with interrupt-driven TX and buffered RX handling.

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✨ Features

• ✅ 128-byte packet mode (XMODEM-128)
• ✅ CRC16 and Checksum support
• ✅ UART-based send/receive with STM32 HAL
• ✅ Built-in timeout management for TX/RX
• ✅ Clear error codes for timeout, cancel, and retransmission
• ✅ Configurable packet size and retry count

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📂 File Structure

├── XMODEM.c // Core implementation ├── XMODEM.h // Header definitions (enums, error codes, prototypes) ├── main.c // Example usage (integrate into STM32 project)

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⚙️ Configuration

Update the UART handle in XMODEM.c to match your project setup:

#define Xmodem_Uart huart6   // Change this to your UART instance
Note: Ensure that the UART instance is initialized in interrupt mode before using this library.

🚀 API Overview
Send Data
c
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int xmodem_send(uint8_t *data, uint32_t length, uint32_t timeout_ms);
Sends a buffer using the XMODEM protocol.

Returns:

XMODEM_OK – success

XMODEM_ERR_TIMEOUT – operation timed out

XMODEM_ERR_CANCEL – transfer canceled

Receive Data
c
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int xmodem_receive(uint8_t *dest, uint32_t max_len, uint32_t timeout_ms);
Receives data via the XMODEM protocol.

Returns:

> 0 – number of bytes received

XMODEM_ERR_TIMEOUT – operation timed out

XMODEM_ERR_CANCEL – transfer canceled

Send CRC Request
c
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void xm_c_send(void);
Sends the 'C' character to request a CRC-based transfer from the sender.

📋 Example Usage
Sending
c
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uint8_t buffer[] = "Hello, XMODEM!";
if (xmodem_send(buffer, sizeof(buffer), 10000) == XMODEM_OK) {
    printf("Transfer successful!\n");
} else {
    printf("Transfer failed.\n");
}
Receiving
c
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uint8_t rx_buffer[1024];
int len = xmodem_receive(rx_buffer, sizeof(rx_buffer), 15000);
if (len > 0) {
    printf("Received %d bytes via XMODEM.\n", len);
} else {
    printf("Receive failed.\n");
}
🔧 Dependencies
STM32 HAL drivers

Configured UART instance with interrupts enabled

📌 Notes
Default packet size: 128 bytes

Retries per packet: 10

Timeout values configurable in XMODEM.c

Padding for short packets: 0x00 (modifiable)

👉 This library is intended to be portable, lightweight, and easy to integrate into STM32 projects requiring reliable file/data transfers over UART.