My ploy with running gamepad-tool on the Linux laptop worked and I was able to get the correct mappings to use in my game. Though weirdly it seems to have X and Y buttons mixed up as well as A and B.

In the end I hard-coded the mapping string and set it up with this code:

	if (SDL_GameControllerAddMapping("030000001008000001e5000010010000,NEXT SNES Controller2,platform:Linux,a:b2,b:b1,x:b3,y:b0,back:b8,start:b9,leftshoulder:b4,rightshoulder:b5,dpup:-a1,dpdown:+a1,dpleft:-a0,dpright:+a0")==-1){
		LogError("Unable to load gamepad mappings from gamepad.txt");
	}

Then in my ProcessEvents() function which handles I/O events, I added this code:

			case SDL_CONTROLLERBUTTONDOWN:
			if (event.cbutton.state== SDL_PRESSED){
				switch(event.cbutton.button){
					case SDL_CONTROLLER_BUTTON_A:
					    fireFlag =1;
					    break;
					case SDL_CONTROLLER_BUTTON_B:						
					    jumpFlag =1;
					    break;
					case SDL_CONTROLLER_BUTTON_X:
					    shieldFlag =1;
					    break;
					case SDL_CONTROLLER_BUTTON_Y:						
					    thrustFlag =1;
					    break;						
					case SDL_CONTROLLER_BUTTON_LEFTSHOULDER:
					    rotateFlag = 1;
					    break;
					case SDL_CONTROLLER_BUTTON_RIGHTSHOULDER:
					    rotateFlag= 2;				
					    break;
					}
				}

There’s similar code for the SDL_CONTROLLERBUTTONUP except it checks for the state = SDL_RELEASED and in the switch statement it sets each flag to 0. So inspite of the code, it’s the Y button that does shields and the X button does thrust, B button fires and A button does the hyper space jump.