Level 9 Electron experiments

[davidb]

I might as well post this here, even though it's a work in progress...

I was disappointed that a lot of adventures for the BBC Micro use MODE 7 because this makes them unsuitable for the Electron. It is possible to do tricks with moving the screen start address to low memory and using the often unused pages from &B00 to &E00 to display the text, but it's not ideal. I imagine that it many of them would run if the screen memory was in shadow RAM - i.e. the OS writes to visible RAM while peeks and pokes go to the main RAM.

With that in mind, I hacked Red Moon to work from ROM cartridge. It still copies a lot of stuff into RAM but we can reclaim a lot of the memory from &6000 upwards. I don't know if I've caught everything that needs relocating but I'm hoping experts can let me know if they see anything wrong with the conversion.

[lurkio]

I hacked Red Moon to work from ROM cartridge. It still copies a lot of stuff into RAM but we can reclaim a lot of the memory from &6000 upwards. I don't know if I've caught everything that needs relocating but I'm hoping experts can let me know if they see anything wrong with the conversion.

I don't know how to configure ElectrEm, and I can't seem to get Elkulator to work at all, so I wasn't able to test your conversion using either of those apps, but I did manage to load the ROMs into BeebEm and run the game using the command *REDMOON -- which was a lucky guess by me, as I don't think I've ever used any of your cartridge ROMs before!

First impressions: Impressive!



The visible "garbage"/data on load is intentional, I presume?

[davidb]

First impressions: Impressive!

Thanks! I learned a bit about the structure of the game engine doing this.

The visible "garbage"/data on load is intentional, I presume?

Yes, it doesn't quite free up memory above &6000, so there is some residual data on screen. It may be safe to move the game data further down in memory if I can determine whether the address &17FF is actually the original value for the top of the game workspace or if it's just some spurious value in a table. Maybe I should look at the length of saved game files and resolve this once and for all!

[davidb]

It may be safe to move the game data further down in memory if I can determine whether the address &17FF is actually the original value for the top of the game workspace or if it's just some spurious value in a table. Maybe I should look at the length of saved game files and resolve this once and for all!

It looks like the save game files are &5FF bytes in length, so no more immediate memory savings are available. The residual data will have to stay for now.