Slot-2 Motion Pak, Guitar Grip emulation

[asiekierka]

This PR adds emulation of the following Slot-2 devices:

• The homebrew Motion Pak, supporting X/Y/Z acceleration and Z rotation measurements. I have validated, with the help of a friend, the X/Y/Z acceleration support; I do not have any hardware which supports the Z rotation, however, so that's a bit of a guess.
  • The Motion Pak is mapped to accelerometer/gyroscope readouts from the connected SDL game controller; think DualSense or Switch Pro Controller.
• The official Motion Pack (sic!), as bundled with Tony Hawk's Motion, as described in Tony Hawk's Motion (USA) missing motion pak #74 . There's really no reason to use that one - it omits the gyroscope, has only 8 bits and not 12 bits of accuracy, and for some bizarre reason the game itself supports the homebrew pak too (!?). I have not tested it, as I don't own the game.
• The Guitar Grip. This is a "low-hanging fruit" with regards to adding other devices that support external inputs, such as the Paddle and Piano Controller. Tested, but only with a homebrew test ROM.

Closes #74 and #73 . Related to #755 . Testing welcome.

[xperia64]

You may have a hard time here as I'm not entirely convinced the homebrew Slot2 motion pack was ever actually sold/made available. The only product I can find with a motion pack is supposedly the Neoflash "R6Gold".

All of my knowledge of the homebrew cart's spec comes from libnds.

[asiekierka]

You may have a hard time here as I'm not entirely convinced the homebrew Slot2 motion pack was ever actually sold/made available.

Absolutely was. https://web.archive.org/web/20080509173200/http://www.ndsmotion.com/ has a list of stores and photos of the packaging.

The problem is that these types of products (the DSerial Edge has a similar problem) were predominantly popular with homebrew developers themselves, so not only did they probably sell in highly limited qualities, they're unlikely to pop up on the second-hand market due to personal nostalgia.

There were six products in total which featured Kionix's technology, five of which were for the DS family of consoles; I maintain a list here: https://wiki.asie.pl/doku.php?id=notes:flashcart:ds_motion_card - of those, the GBAccelerometer is the easiest to find (it's still available in stock in 2024), but that's not a DS product; next, there's the Activision pak, and after that probably the R6 Gold?

I tested with an MK6-Motion myself, which happens to feature both the accelerometer and gyroscope chip; since the chips themselves and thus values output should be identical between the Card and a Pak, I deemed the emulation to be accurate enough for running homebrew (which is the important thing for me from a preservation perspective), but I can't verify fine details like the Pak's open bus behaviour or any additional SPI/ROM commands the Card might have.

All of my knowledge of the homebrew cart's spec comes from libnds.

There's some additional bits of information in a README bundled with the original DS Motion Card/Pak driver source code on said website.

[asiekierka]

(Either way, I don't expect this to be resolved as part of this PR, and the detection mechanism used by all homebrew for the Pak doesn't rely on open bus behaviour.)