Multidesk 64

tl;dr: This tool can make a 5-in-1 MagicDesk cart with a simple selection menu. Requires minimal coding and only works with SOME MagicDesk carts. The files you need can be found here: MultideskV1.zip

Introduction

Multidesk 64 is a small brute force hack that was developed for the Oneload64 project, but is not limited to that. The idea for this is to combine several MagicDesk cartridges into one Multi-Cart. This is, of course, impossible.

The MagicDesk format is a simple and effective bank-switching cartridge. It shows up in the memory space of $8000 to $9FFF and a simple write into $DE00 switches into that bank. There is no protection against switching into no-existant banks and there is no way to find out which bank is currently active, as reads from $DE00 will make uncontrollable bank switches. It is a bare-bones as it gets. Oh, and writing a value higher than $7F will switch the cart off. This gives you 64 banks of 8K each.

Because of its simplicity, the format has been adapted by several projects to create fast starting games for emulators. The three main projects are:

• OneLoad64 with literally thousands of games in MagicDesk format
• MagicDesk CRT Linker which allows to convert VICE freezes into cartridges
• T64 to CRT, my own project to convert tape-based software into cartridges

Most C64 games just load once and then never need to access a disk or tape. Many C64 games require constant loading of parts from disc or tape. And then there are some C64 games that consist of several parts which the user most load themselves. Sometimes the two sides of a tape have different versions of a game, sometimes you need to play through Part 1, receive a password, manually load Part 2 and then type in that password to continue. Those games so far were also split into several cartridges in the OneLoad collection and I wanted to change that.

MultiDesk 64 is a very simple boot menu that uses just the first bank of a MagicDesk cart (Bank #0). It shows a menu that can switch to up to five (well, up to six) other MagicDesk carts.

The trick is that these other carts have to be patched. They need to know that they start in a different bank. This requires either reassembling or patching the carts. For the first release, there are methods to use carts from the OneLoad64 project and those created with CRT_Linker. More will follow early 2026 (including my T64 project and the MagicDesk carts created by TheJoker).

Basically this is all that happens:

• Show menu
• Set Bank to the Cart user selected
• Call Reset, user selected Cart starts (and crashes if unpatched)

The menu

The menu code is split in two parts for the ACME assembler. Everything you need to touch for your cart is in assets.asm but you need to compile multidesk_menu.asm which includes the data file. Most options are self explanatory, but here is the rundown:

• You need to set whether the games you load require Joystick Port #1 or #2/keyboard. This avoids that the menu uses a different port than the game itself. Sorry, no mix and match. If you need keyboard, use #2.
• Standard timeout for automatic selection is 500 frames, or 10 PAL seconds.
• Colors as standard
• TxtGameName: max 38 characters for the name of the complilation, displays line #6
• TxtComment: max 38 characters for the bottom line
• ITEM_COUNT: The number of menu items to use. Max is 5, 6 when you leave TxtCommentempty (e.g. it has at least one whitespace but no letters)
• MenuTextBase: Zero delimited, small letters only (PETSCII), 38 chars max. It does not hurt to have MORE entries here, but it will hurt badly if you have less then ITEM_COUNT.
• MenuBanks: The bank numbers for the menu lines. So, if you select the first item, the bank will be #01 (most likely always). The second item needs to be the bank the second entry will be in the final cartridge, more to that later.
• TxtInstructions: Can be changed if you need something else then Joy #1 / Joy #2 text
• map_data and map_colour_data: feel free to include any other PETSCII screen here. Standard format as output by most editors if you want assembler code.

Patching OneLoad64 games

If you want to combine several games from OneLoad64 into one cart, you need the cartconv.exe from VICE as well as a Python interpreter and the provided "oneload.py" script. The first menu item would live in bank 1, to patch it you simply do this:

cartconv -i CARTNAME.crt -o CARTNAME.bin

python oneload.py CARTNAME 1

There will be several checks and then you have a patched CARTNAME.bin. This will most likey be 64K, 80K or 88K long. This is either 8, 10 or 11 banks. So, as we have started in bank 1, this goes to 9, 11 or 12. Meaning, the next cart starts at 10, 12 or 13.

For the game Deliverance: Stormlord II we get to the following numbers:

So the starting bank numbers for assets.asm are 1, 12 and 23.

And the bin for Level 3 & 4 needs to be patched with 12:

python oneload.py LEVEL34.bin 12

and equivalent for 5 & 6 with 23.

After compiling the menu with ACME, you will receive a file boot.bin. Use a binary copy command to connect all files together. This can be used for EPROM burning. To use this cartridge in VICE we need to cartconv again.

copy / b boot.bin + level12.bin + level34.bin + level56.bin deliverance.bin

cartconv -i deliverance.bin - o deliverance.crt -t md -p

Do not forget the -p parameter, as the cartridge will be "odd sized".

Combining CRT_Linker Games

If you are using CRT_Linker from Pugsy to create your own carts, you can create them directly for different banks. The output from this tool is preformatted so you do not need the cartconv steps and can do straight copies. Here's how to proceed:

Get V17 (or later) of CRT_Linker: New Release: Magic Desk CRT Linker (make your own CRTs) - Page 11 - Commodore 64 - Lemon64 - Commodore 64

In multidesk_menu.asm set the parameter VICEHEADERto 1. (By pure chance this is in line 64 :-). This will build a stub boot.crt file rather then a .bin.

For the first game in the menu, call CRT_Linker with the -bank01 parameter:

crt_linker 1.freeze.vsf 1.crt -bank01

As the files created can have different lengths, the linker will tell you in which bank the next game should start. 

Saving headerless CRT with banks numbered from 1 to 8
Create next game crt with -bank09

So here we go with

crt_linker 2.freeze.vsf 2.crt -bank09

Please write down the bank numbers, these are the numbers you need to set in assets.asm

You can now simply binary copy and combine without using cartconv:

copy /b boot.crt + 1.crt + 2.crt compilation.crt

Ready!

Future work:

I wanted to have this ready for the next OneLoad64 release, so this is not yet an automatic tool. In early 2026, if there are request for it, these additions will be made:

• Patcher for T64 to MagicDesk carts (including those from TheJoker).
• More automatic conversion scripts for sets of cartridges.
• Direct patching of the boot stub with menu text without needing ACME.