xrecv.exe README

xrecv.exe is a minimal XMODEM Checksum receiver for Windows 98, designed specifically for recovery scenarios where the system can only operate in Safe Mode and lacks access to normal file transfer methods (no USB, no LAN, no CD/DVD, no floppy). It enables transferring binary files (DLL/EXE) over a serial port using a second machine (e.g., Ubuntu/Linux).

This document describes:

• What xrecv.exe does
• How to compile xrecv.c using mingw-w64 on Linux
• How to deliver the EXE to Windows 98 using a DEBUG script
• How to perform XMODEM transfers from Linux to Win98

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1. Overview

xrecv.exe provides a lightweight implementation of XMODEM (128-byte, checksum mode) and writes the received binary data to a file.

Supported protocol features

• SOH (0x01) for block start (128-byte)
• EOT (0x04) for transfer end
• ACK (0x06) on valid block
• NAK (0x15) on checksum or header error
• Block number and inverse (0xFF - blk)
• Simple checksum

Serial settings (fixed)

• 38400 baud
• 8 data bits, no parity, 1 stop bit (8N1)
• Flow Control Off (no RTS/CTS, no XON/XOFF)

Target use case

This tool is intended for scenarios such as:

• Windows 98 system boots only in Safe Mode
• Network stack is broken (e.g., missing msnp32.dll)
• No working floppy, CD-R, USB, PCMCIA
• Only COM1/COM2 works

In such cases, xrecv.exe allows recovery of critical system files.

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2. Usage (on Windows 98)

Command format:

xrecv COM1 output.bin
xrecv COM2 msnp32.dll

• Argument 1: COM port name (COM1–COM4)
• Argument 2: Output file name (binary)

Example:

xrecv COM1 msnp32.dll

This puts xrecv.exe into waiting mode, where it repeatedly sends NAK until the sender begins transmitting.

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3. Compiling on Ubuntu/Linux

3.1 Install mingw-w64

sudo apt update
sudo apt install mingw-w64

3.2 Compile

i686-w64-mingw32-gcc -Os -s -o xrecv.exe xrecv.c

• -Os: Optimize for size
• -s : Strip symbols to minimize EXE size

3.3 Verify

ls -l xrecv.exe

The resulting binary is safe to reconstruct via Windows 98 debug.exe.

3.4 Compile via helper script

You can also use the bundled helper:

./build.sh               # builds xrecv.exe
./build.sh --debug-script    # builds xrecv.exe + xrecv_dbg.txt

• --debug-script additionally produces xrecv.hex and a DEBUG script (xrecv_dbg.txt) using make_debug_script.py. The script defaults to emitting XRECV.EXE inside the DEBUG recipe.

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4. Delivering xrecv.exe to Windows 98 Using DEBUG

If you cannot copy the file normally, you can re-create the binary using a DEBUG script.

1. Convert binary to hex text:

   xxd -p xrecv.exe > xrecv.hex

2. Generate a DEBUG script (CR+LF required):

   python3 make_debug_script.py xrecv.hex XRECV.EXE > xrecv_dbg.txt

3. Transfer xrecv_dbg.txt to Windows 98 via plain ASCII serial transfer (e.g., using COPY COM1:).

4. On Windows 98:

   debug < xrecv_dbg.txt

This reconstructs XRECV.EXE in the current directory.

4.1 About make_debug_script.py

make_debug_script.py converts a plain hex dump (e.g., xxd -p output) into a DEBUG script that:

• writes the bytes starting at 0100h (DEBUG load address)
• sets CX to the binary size
• saves the file with the name you pass as the second argument
• emits all lines with CR+LF endings (as required by DEBUG)

Usage:

python3 make_debug_script.py INPUT.hex OUTPUT.EXE > script.txt

Use the generated script.txt with debug < script.txt on Windows 98 to re-create the executable.

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5. Sending Files from Ubuntu using XMODEM

5.1 Configure the serial port

sudo stty -F /dev/ttyUSB0 38400 cs8 -parenb -cstopb -ixon -ixoff -crtscts

5.2 Start minicom

sudo minicom -s

Set:

• Serial port: /dev/ttyUSB0
• 38400 8N1
• Hardware Flow Control: No
• Software Flow Control: No

5.3 Run xrecv on Windows 98

xrecv COM1 msnp32.dll

5.4 Send file from Ubuntu (inside minicom)

1. Press Ctrl+A → S (Send)
2. Choose xmodem (checksum mode)
3. Select msnp32.dll
4. Press Enter

When the transfer completes, Win98 will show:

Completed.

A new file msnp32.dll will appear in the current directory.

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6. Verification

6.1 File size check

Ubuntu:

ls -l msnp32.dll

Windows 98:

dir msnp32.dll

Sizes must match.

6.2 Optional: double-transfer comparison

xrecv COM1 msnp32a.dll
xrecv COM1 msnp32b.dll
fc /b msnp32a.dll msnp32b.dll

If FC /B reports no differences, your transfer is fully reliable.

6.3 Optional: use a lower baud rate

If errors occur, use 9600 baud on both sides.

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7. Limitations

xrecv.exe is intentionally minimal. It lacks:

• CRC XMODEM
• XMODEM-1k support
• CAN-based session abort
• Advanced block number handling (only basic validation)

However, for short-range cable transfers in a recovery scenario, it is sufficiently robust.

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8. Typical Full Recovery Workflow

1. Build xrecv.exe on Ubuntu
2. Convert to HEX
3. Generate DEBUG script (CR+LF)
4. Send script to Win98
5. Rebuild XRECV.EXE using DEBUG
6. Run xrecv COM1 target.dll
7. Send DLL via XMODEM from Ubuntu
8. Place DLL into the correct Win98 system directory and reboot

This restores broken components (like msnp32.dll) while avoiding all non-working devices.

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9. License

This project is released under the MIT License (see MIT LICENSE.txt).