[erik]

I made a few small contributions to this a long time ago. Nice to see that the website is still up!

Probably the most interesting feature of this project was how it handled memory. The DS only has 4mb of ram. And there is no MMU, so swap isn't an option. But the gameboy cartridge port has 32mb of address space mapped to the bus. And there are homebrew/piracy cartridges that fill that space with 32mb of ram. Which is great, except that the DS can only write to the cartridge port on 16-bit aligned addresses. And almost all software will assume that 8-bit aligned writes will work. To make use of the expansion memory the developers ended up creating a patched GCC that would convert any writes to unaligned locations to an appropriate read, 16-bit write, and set of shift operations.

[MenhirMike]

> And there are homebrew/piracy cartridges that fill that space with 32mb of ram.

There's even an official one, the Opera Web Browser came with a second cartridge for the "GBA" slot to add 8 MB of RAM and a MMU: https://en.wikipedia.org/wiki/Nintendo_DS_Browser#Memory_Exp...

(I've long lost the Opera DS cartridge, but the memory expansion is still in my DS Lite as a slot cover)

[monocasa]

Huh, does it really have an MMU? I don't remember that when I coded for it back in the day, and wiki seems to be the only one saying that (uncited). It also doesn't make a lot of sense to be at that point in the system as it's so far away from the main bus matrix.

But perhaps my memory is going bad and my Google Fu is worse.

Edit: gbatek doesn't document an MMU in those cards either. https://problemkaputt.de/gbatek.htm#dscartexpansionram

[erik]

I think wikipedia is wrong. I don’t see how it would make sense to have a mmu in the ram expansion card.

[MenhirMike]

I have no idea, just quoted Wikipedia. It looks like there is only a single chip in that module, so it would make sense for that only being a RAM chip. Can't edit the post anymore though.

[erik]

We were pretty proud that we had a graphical browser running under DSLinux a good 6 months before Nintendo released the Opera cart.

[Operyl]

Haha! I always wondered as a kid why that was a requirement. The number of times I had to use the Opera browser to get around my restrictive mother, sigh.

[erik]

Another quirk: It was pretty common to load your homebrew software from a cartridge in the gameboy port. The cartridges would have some combination of ram and flash based storage or CF Card, and you could tell the cartridge to expose the storage or the ram as they were behind some sort of banking scheme. This meant that the storage system was mapped directly to the bus. So to save on ram, programs were run "in place", executing directly from the storage rather than being copied to ram first.

[joshumax]

I very fondly remember this project when I was growing up too, and I credit it with sparking my interest in kernel development.

When trying to port some industrial control software to DSLinux, I ran into some bugs around how the SLOB allocator behaved under memory pressure. One of my patches landed upstream, even though SLOB is deprecated now. Still, as a kid starting out in the embedded space, it opened my eyes to the joys of hacking around with homebrew.

Fun fact: a modded DS still powers a large part of my local observatory's equipment.

[dormento]

> Fun fact: a modded DS still powers a large part of my local observatory's equipment.

I'm interested! I'd like to read more about that.