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mcendu
Posted on 11-21-22 07:03 AM Link | #5650

Hello.

...

The Nintendo DS features backward compatibility with the GBA. This leaves me to wonder: How does the DS achieve backward compatibility? What happens when the player clicks "Start GBA game." and when the DS powers up with an empty DS slot and a GBA game?

Currently, the emulated DS of melonDS crashes when it attempts to boot into a GBA game. Once the process of starting a GBA game is known, how much work would it take for a basic emulation?

I am just leaving these questions here, but I hope these would be interesting to look into. Thanks.



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CasualPokePlayer
Posted on 11-21-22 07:05 AM Link | #5651
The DS has an entire GBA bundled in it. For melonDS to support GBA games, it would practically need to make a brand new GBA emulator. At which point, just use a dedicated GBA emulator like mGBA.

mcendu
Posted on 11-21-22 07:20 AM Link | #5652

...That a GBA is bundled in the DS is too obvious an answer to me.

What I am looking for is the gory details behind, like which DS hardware is active when running as a GBA and which aren't, and how does the DS enter GBA mode. This is mainly relevant for completeness as GBA mode is part of the DS hardware.



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patataofcourse
Posted on 11-21-22 08:00 AM Link | #5653
it really doesnt matter though (in the sense of melonDS): GBA mode support would mean basically creating a new emulator inside melonDS, which would have its own bugs and issues, and it's a whole other can of worms. unless mgba gets integrated into melonDS for this stuff don't expect this to happen in the near future
if you wanna know more about this try looking up the GBA mode information in gbatek, iirc it gets started by setting a register? but yeah the hardware side is just. the DS builds on GBA hardware, and they probably added some more GBA-exclusive hardware to ensure compatibility. all i can say abt unused hardware is that the ARM9 processor is obviously not used in GBA mode

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Generic aka RSDuck
Posted on 11-21-22 09:24 AM Link | #5654
for the most part the DS is a superset of the GBA (except for the very basic sound hw the GBA has). So it's not like the DS switches to completely different hardware when it goes into GBA mode. For the most part it just switches things off (the ARM9, 3D engine, second PPU and some features of the first PPU, the new sound engine, ...) and switches to a different memory map.

Like patataofcourse said though, while putting together a basic GBA emulator from the parts of a DS emulator is not that hard, but making a good one is very hard, because timing can work very differently/different things are important for good emulation compared to DS (e.g. you don't really need to emulate prefetch for DS, because games practically never run off cartridge, while they do almost exclusively on GBA).

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Main - Development - On the compatibility with GBA Hide post layouts | New reply

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