Hacking Custom GBA cartridge

[bidouille]

Hi,

I'd like to build a custom GBA cartridge to attach some hardware, like a keyboard, to a DS.
I'm looking for some pointer as how to access the GBA port from the DS. Has this kind of thing already been done?
I need to know also what maximum current I can draw from the GBA port without risking to fry it. Is this information known?

On a related note, what is the state of the dslinux project? Is it still active?

Thanks.