Microchess for the RP6502 SBC

Peter Jennings' Microchess built for the RP6502 SBC using the RP6502 tool-chain and the cc65/ca65 assembler.

Source-code Reference and Historical Information: www.benlo.com/microchess/.

Also see the User Manual available at the above link and in the 'docs' sub-directory herein.

Quick-start information derived from Daryl Rictor's Aug-2002 port & Readme:

Microchess was developed in 1976 originally for the KIM-1. Later versions included 1.5 ported to the Commodore PET and Commodore Chessmate; and 2.0 for the Apple II and the Tandy Color Computer series. A pdf of a scanned copy of the original source code is included in the reference_code directory for those who wish to study the program's logic and strategy.

To play, load the program into the RP6502 SBC as any other executable. The program's starting address's is $0200 and is just under 1.5k. (Best to inspect the mapfile for addresses just to be sure.)

On startup, you'll see a welcome-banner. Note, the board was designed to be viewed using a white text on dark background. Therefore, the empty squares that are white will have ** in them, while the black squares are filled with spaces. Hopefully, this won't confuse everyone. If it does, then feel free to alter the code just before label 'POUT25' to reverse the characters.

Commands are:

• C - clear and restart the game (when entered, CC CC CC will appear)
• E - toggle sides (when entered, EE EE EE will appear)
• P - tell the computer to "Play Chess". By default, the computer will play white. To play black, after clearing the game, press E to switch sides, enter your move (as described below), and then press P.
• [Enter] - give the computer YOUR move
• Q - Quit the Game (JMP's to address $E800 (the SBC monitor entry point)

You must clear (i.e. reset) the game when you play it for the first time in a session. The game is not cleared automatically for you when you start the program.

The computer will display its move in ax yy zz format, where 'a' is the player (0 if computer, 1 if yours) 'x' is the chess piece (zero-page memory locations of your pieces and the computer's pieces in parentheses):

0: King            (you, 0060; computer, 0050)
1: Queen           (you, 0061; computer, 0051)
2: King's Rook     (you, 0062; computer, 0052)
3: Queen's Rook     :
4: King's Bishop    :
5: Queen's Bishop   :
6: King's Knight    :
7: Queen's Knight   :
8: K R Pawn         :
9: Q R Pawn         :
A: K N Pawn         :
B: Q N Pawn         :
C: K B Pawn         :
D: Q B Pawn         :
E: Q Pawn           :
F: K Pawn          (you, 006F; computer, 005F)

'yy' and 'zz' are the from and to square respectively. Each ranges from 00 to 77, with 00 being the computer's queen rook, and 77 being your king rook.

For example, the move 0F 13 33 means King's Pawn from King's Pawn 2 to King's Pawn 4 (white). The computer may take some time to compute its move and will print dots (.) as it thinks.

To enter your move, enter FROM and TO locations (piece is not needed). The computer verifies your piece by showing what is on that FROM square; if it is one of your men, it will start with a 1. (An FF shows no piece there.) For example, should you key 63 43 and the screen reads 1F 63 43, that means KIM thinks your King's Pawn is there and that you're advancing it two spaces. When ready, press to enter the move, and then 'P' to tell the computer to play. The legality of your moves is never verified, and you may make multiple moves on a single turn -- as long as you press after each one -- before pressing 'P' (in fact, as you'll see below, for special moves you will have to). You may move the computer's men at any time as well. The computer also does not warn you if you are in check, and its strategy expects that you will move out of check when you are placed in it.

Castling is accomplished by moving the king, then rook, then pressing 'P'. If the computer signals a castle by moving its king two spaces over, you will need to also move its rook for it.

While you of course can capture en passant by making the appropriate lateral capture and moving forward, the computer does not know how and will not construct its strategy with it in mind.

Queening pawns must be done manually by altering the game board image from the SBC monitor. Stop the game with 'Q', remove the queened pawn by entering CC in its location (see table above) and set your Queen at 0061 to this queened pawn. After adjustment, restart the game. As only one Queen can be on the board at once, if you still have a Queen you must select some other captured piece and then move that as if it were a queen. The computer will also not autopromote its queened pawns, so you'll have to do that as well.

The computer will resign if it ends up in checkmate or stalemate; the display will read 'ff ff ff'. You are, of course, expected to show the same courtesy when you are checkmated, and restart the game.

[Edit: addresses below need updating for the RP6502 SBC; consult mapfile.]

There are a few points of adjustment for skill level. By default, 08 at $11F5 and FB at $10DE indicates normal mode with an average time per move of ~100s. If you are an impatient or poor player, try 00/FB for ~10 seconds "Blitz", or 00/FF for ~3 seconds "Super-Blitz". Of course, the computer's ability to analyse moves will be progressively impaired.

Openings can be loaded into locations $1541-$155C which Microchess will attempt to play from, as long as you do. By default, the game will try to play the Giuoco Piano opening.

Reference - RP6502 VS Code Scaffolding for CC65 tool-chain:

This provides scaffolding for a new Picocomputer 6502 software project. Both C and assembly examples of "Hello, world!" are included. Make sure CMakeLists.txt points to your choice of main.c or main.s, then delete the one you aren't using.

Linux Tools Install:

• VS Code - This has its own installer.
• A source build of CC65.
• The following tools installed from your package managers:
  • sudo apt install cmake python3 pip git build-essential
  • pip install pyserial

Windows Tools Install:

• winget install -e --id Microsoft.VisualStudioCode
• winget install -e --id Git.Git
• winget install -e --id Kitware.CMake
• winget install -e --id GnuWin32.Make Add C:\Program Files (x86)\GnuWin32\bin to your PATH.
• The current snapshot of CC65 - Do not skip the step about adding the bin directory to your PATH.
• Install Python by typing python3 in a command prompt, which will launch the Microsoft Store where you can start the installation. If Python runs, this has already been done — exit Python with Ctrl-Z plus Enter.
• pip install pyserial

Getting Started:

Go to the GitHub template and select "Use this template" then "Create a new repository". GitHub will create a clean project for you to start with. Then you can clone the repository and open the files.

$ git clone [path_to_github]
$ cd [to_where_it_cloned]
$ code .

Install the recommended extensions when VS Code prompts you, choosing the default or obvious choice for any other prompts. The tools we use in VS Code are constantly improving and changing making it too difficult to maintain documentation.

"Start Debugging" (F5) will build your project and run it on a Picocomputer. Connect with a USB cable plugged into the RP6502-VGA USB port.

If you get a Python error about the communications device not being found, edit .rp6502 in the project root. This file will be created the first time you "Start Debugging" and will be ignored by git.

Once the program is running, a debug console becomes available on the terminal tab. It will say "Python Debug Console" because the rp6502.py tool is Python. Ctrl-A then X will exit. Ctrl-A then B will send a break.

Edit CMakeLists.txt to add new source and asset files. From here on, it's standard C/assembly development for the 6502 platform.