This is the first time I hear that a game is not running on the U2+
Could you explain the technical reason for that? just interested to understand. No critism!
The game is great!
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Hi Gregor,
Thank you and thanks for asking!
I wish it could support it. I suspect there's two reasons. I looked over the U2+ specs and under "C64 cartridge emulation, with support for many CRT files" it lists "Custom Ocean / System3 carts (up to 512K)". This makes me wonder if there's not sufficient onboard RAM/flash to support larger cartridges (as this one is > 512K). The other issue concern is that this cartridge format is a Magic Desk 2 cartridge format, configured at 8Mb (1MB), and I do not explicitly see this in the list. It might be this particular data file format is not supported (yet).
The same issue will present itself with any device that attempts to emulate cartridges, for example the Mini or the Maxi. They need to have sufficient space available to load the cartridge and bank in/out data "on-demand" and support the particular .crt file format for Magic Desk 2 at this capacity. Newer VICE versions supports this format, but it's not universal (yet + unfortunately).
For those wanting to understand the low level details, technically the game is a compiled 1MB binary (.bin) file with all the code, graphics, text and sound inside. I use the VICE cartridge converter to convert that binary file into a magic desk 2 .crt file. There's nothing special at all about this binary file otherwise. The binary file is 128 x 8K binary chunks merged (in-order) together into a single file then converted into a .crt files where meta data describing the contents of the cartridge format is added.
For the Magic Desk 2 format, a cartridge emulator (e.g. U2+, Maxi/Mini) needs to respond to requests when the game code sets a bank value at $DE00. The game code effectively does an LDA #bank STA $DE00 (or to translate to BASIC, a POKE 56832, <bank>). Then the cartridge emulator responds by presenting one of the 8K bank out of the 128 available as ROM memory at location $8000 for the C64 CPU. So the U2+ and Maxi/Mini need to add this tiny bit of logic and have the space in RAM/flash to be able to load this cartridge. Cartridge emulators already do this type of logic for other cartridges, so it would be very easy to support Magic Desk 2 if they have the RAM/flash space available to hold this size cartridge.
I hope this helps explain!
Interesting. I looked at the firmware code, and I see that the the max rom capacity for the U2+ is 1MB, and they do support Magic Desk but the comment says that it supports a max of 16 x 16K chunks, which means 256K total. So they do support some banking but not the full range. Probably a very easy fix.