lr-FCEUMM: Space Shadow + Bandai Hyper Shot (setup guide + question)

[ChaosEffect]

Pi Model or other hardware: Pi 3B
Power Supply used: Smraza 2.5A
RetroPie Version Used: 4.7.1
Built From: Pre-made SD Image on RetroPie website
USB Devices connected: Wireless keyboard/mouse combo, 8BitDo wired controller, Sinden lightgun
Controller used: wired 8BitDo SN30 Pro, Sinden lightgun
Emulator: lr-FCEUMM

Hello,

I thought I'd pass along some information I found while tinkering. I also have some questions about RetroArch controls.

Space Shadow on the Famicom uses the Bandai Hyper Shot peripheral, which is a machine-gun controller that has a D-pad; a trigger; and B, start, and select buttons (so it's essentially a full controller with a trigger button instead of an A button).

lr-FCEUMM has a Hyper Shot option for player 5 (on real hardware, the gun would be plugged into the Famicom's extension port, and this is how lr-FCEUMM handles those peripherals). The gun appears to assume control over player 1's buttons. On my Sinden lightgun, I can assign the D-pad, trigger, and start/select to the appropriate player 1 buttons and can use them in game. Hopefully that helps anyone who had tried to play this game but couldn't get it to work. The Zapper option does not appear to work at all with this game.

Now, for my two questions. My controller's B button can be used to throw bombs in Space Shadow, but assigning the B button to any mouse or keyboard button does nothing. However, if I assign TURBO B instead, the bomb works on both keyboard and mouse buttons. I have to make these changes either in Settings -> Input or by manually editing the game.cfg file. Whenever I save a game override within RetroArch, the input changes are deleted. That is fine. I can edit the config manually. However, I don't see an individual entry for "TURBO B" (or A) anywhere. Is there a line I can add to my config that will map to TURBO B? I am aware that no subscript on these lines means keyboard mapping, "btn" as a subscript means controller, and "mbtn" as a subscript means mouse.

My second question is related to the trigger. I can repeatedly pull the trigger to get shots in rapid succession, but Space Shadow was meant to allow automatic fire by holding the trigger button pressed. I can't seem to get that to work. The issue with the B button makes me think I need to enable a turbo mode for the trigger, but I can't seem to get that to work (or I just misunderstand how the turbo functionality works). The Sinden gun works fine with holding the trigger down in other libretro cores, so this appears to be an emulator issue. Is there a way to get turbo functionality on a mouse button? My attempt was to enable turbo for player 1 and set mouse 1 to both the trigger and turbo buttons in hopes that holding mouse 1 down would simultaneously fire and activate turbo, but that didn't work for me.

Any insight would be greatly appreciated!