[KurdtNervanna]

The next feature after #14, as one PR (#11): rsos-gamepad, the RetroStone2's built-in controls as one SDL game controller for native games.

Depends on #14. This branch sits on top of #14's branch, so until #14 is merged the diff also shows its two commits. The change for review is the last commit, 4bd2608.

Why

The built-in controls are three input devices: the buttons, the shoulder buttons and the optional analog stick. Many SDL games read only one game controller, so they see only part of the controls. SDL doesn't take the stick for a joystick at all.

What it adds

rsos-gamepad (board/retrostone2/tools/rsos-gamepad.c, built in post-build.sh with -Wall -Wextra -Werror) reads the three devices and writes one standard virtual gamepad through uinput, named "RetroStoneOS Gamepad":

• The face buttons go by position (bottom = SDL "a", left = "x"). L1/R1 are the shoulders, L2/R2 the triggers, and the optional C/Z the stick clicks.
• The D-pad is hat 0.
• The stick is the left stick, centred while it isn't fitted, as in the menu.

It doesn't grab the devices, so the menu still sees Select+Start.

A launch script starts it in the game's process group, so the menu stops it with the game. The script gives SDL the mapping and tells SDL to ignore the raw button device:

SDL_GAMECONTROLLERCONFIG="$(/usr/bin/rsos-gamepad --print-mapping)"
export SDL_GAMECONTROLLERCONFIG
export SDL_GAMECONTROLLER_IGNORE_DEVICES=0x0001/0x0001
/usr/bin/rsos-gamepad &

Kernel: CONFIG_INPUT_UINPUT=y in the RetroStone2 kernel fragment.

Docs: docs/native-games.md gets a section on the built-in controls.

Tests

• It builds for the console with Buildroot's compiler and for the host with -Wall -Wextra -Werror. --print-mapping prints the SDL mapping line.
• check-defconfigs and check-modes pass. shellcheck isn't installed here.

On hardware

Tested on a RetroStone2 Pro with fork builds 0.1.4.18 to 0.1.5.19, which ship this tool. Two SDL2 games built on a PC from the user's own ROMs use it for all their controls:

• a Star Fox 64 port (Starship);
• an Ocarina of Time port (Ship of Harkinian), both on libultraship with GLES2.

Buttons, triggers, D-pad and stick all reach the game. The menu stops the tool together with the game. No game or game data is part of this PR.

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