Since the accelerometer (G-sensor) should be available with the latest firmware I tried to use it.
As much as I know it should be listed as another joystick device: SDL_NumJoysticks() on GCW should read 2, but it still reads 1.
That's because you're missing this parameter in your OPK's .desktop file:
A minimal metadata file should contain the following fields:
So the line "X-OD-NeedsGSensor=true" seems not to be supported?
The key here is "minimal". Meaning that all these mentioned fields are mandatory and must
be present in the .desktop file for GCW Zero to properly load it.
The other fields, like your X-OD-NeedsGSensor=true
are optional and should be set by the OPK creator if the game is going to make use of the feature (in your case the g-sensor).
It would be great if Surkow could add the accelerometer (and the rumble motor as well?) as further examples in the SDL tutorial page.
Rumble isn't supported by SDL 1.2. Only SDL 2.0 has support for rumble devices. Note that this is a limitation of the library and not of GCW Zero. If you want to add rumble support to a non-SDL 2.0 program, you'll need to implement it yourself, by using Linux's Force Feedback: https://www.kernel.org/doc/Documentation/input/ff.txt
Additionally the current firmware has a bug in the rumble driver that makes it vibrate past the effect's run time. I have already provided a patch for this behaviour, but it has not been merged to the driver yet.
PS. The wiki is hosted in surkow.com comain, but it doesn't mean Surkow is the author of all the articles you mentioned. In fact, the SDL 1.2 tutorial was written by me and the OPK documentation by pcercuei