Compaq Portable II/III Russian Font TSR

This repository contains a Terminate and Stay Resident (TSR) program for the Compaq Portable II/III running DOS. It installs a custom 8×16 CP866 (Russian) font and reloads it automatically whenever the BIOS sets a new video mode.

Features

• Loads a custom (Russian) 8×16 CP866 font for DOS text modes.
• Stays resident in memory, hooking INT 10h.
• Automatically detects when AH=0 (set video mode) is called and restores the font.
• Supports text modes: 0, 1, 2, 3, 7, 9 (CGA/EGA text, 40×25 and 80×25).

System Requirements

• DOS 2.0+ (or compatible)
• Compaq Portable II/III or a fully compatible machine (especially for the custom BIOS calls).
• A few kilobytes of conventional DOS memory for the TSR code.

How to Build

1. Make sure you have the YASM assembler installed.

2. A sample Makefile is included. Simply run:

   make

   This will assemble the file (.s or .asm) into a .com binary (e.g., cmp_rle.com), producing a map file as well.

3. Optionally, make clean will remove the .com file and map file.

Usage

1. Copy the generated .com file (e.g., cmp_rle.com) to your DOS environment.
2. Run it from the command prompt:

   C:\> cmp_rle
   

3. The program installs itself as a TSR, hooking INT 10h.
4. Whenever you change the video mode (via MODE, direct INT 10h calls, etc.), if it’s a recognized text mode, the TSR automatically re-loads the Russian font.

Technical Overview

• On load, the TSR calls INT 21h/AH=31h to remain resident.
• It saves the original interrupt vector INT 10h, then replaces it with a custom handler.
• The custom handler checks if AH=0 (set video mode). If so, it installs the font via INT 10h/AH=11h (and possibly AH=14h if needed).
• This ensures the font gets restored whenever DOS or the BIOS re-initializes the screen.

Possible Issues

• If insufficient conventional memory is available, the TSR may fail to install or operate properly.
• Removing the TSR from memory requires either rebooting or using specialized tools like MARK/RELEASE.

Author

• Dmitry Gerasimuk
• [email protected]

Feel free to open issues or pull requests if you have questions or improvements. Enjoy!