This tutorial is based on sections of tutorials listed below.
https://sites.google.com/site/completesg/backup-launchers/gamecube/cmios
https://gbatemp.net/threads/gameboy-advance-original-sp-micro-as-gamecube-controller-for-wii.435282/
https://sdremix.com/installation/gamecube-installation/running-gcn-homebrew/
This requires a Wii U + Gamecube Adapter, and a Wii with Gamecube Ports or a Gamecube capable of running Homebrew!
You'll need to follow these steps each time you want to play using the GBA!
​

1. Extract the ZIP located at the bottom of this post to the root of your SD Card.

Spoiler: Wii Steps

2. Obtain the latest MIOS version using NUS Downloader (the steps are located at the top of the first link).
3. Place the MIOS wad renamed to "RVL-mios-v10.wad" on the root of the SD Card.
4. Remove the SD Card from your computer, and place it into the Wii.
5. Go to Homebrew Channel and launch "Installer for WiiGator's cMIOS."
6. Set the install IOS to IOS 249 and Press A.
7. Press the button it tells you when it pops up.
8. Press the A button for the remaining menus.
9. Launch WiiXplorer and navigate to the SD Card.
10. Click on gbi.dol and select GC Homebrew.
11. Connect your GBA to any port using the Link Cable.
12. Turn the GBA on without a Game in the slot, and wait for the screen to turn blank.
13. Press buttons on the DPad, If the values on the screen change, then that means it worked. If the values don't change, try plugging it into another port.

Spoiler: Gamecube Steps (Untested)

2. Enter Homebrew through your preferred method.
3. Launch gbi.dol.
4. Connect your GBA to any port using the Link Cable.
5. Turn the GBA on without a Game in the slot, and wait for the screen to turn blank.
6. Press buttons on the DPad, If the values on the screen change, then that means it worked. If the values don't change, try plugging it into another port.

The GBA should work if plugged into the GC adapter for a game like Super Smash Bros.
However, you won't be able to control the characters as the DPad is mapped to the normal DPad.
Thankfully there's HID to VPAD! https://github.com/Maschell/hid_to_vpad/releases (or the Wii U Plugin System by Maschell https://github.com/Maschell/WiiUPluginSystem/releases)
I've included an ini file called "GBA Smash.ini" which I have tested with Super Smash Bros. It works somewhat well.

Wii U Steps
1. Take the SD Card out of your Wii/Gamecube and plug it into your computer.
2. Add HID to VPAD to your SD Card.
3. Remove the SD Card from your computer.
4. Plug the SD Card into your Wii U.
5. Launch Homebrew through your preferred method
6. Run HID to VPAD.
7. Assign the GBA to a controller slot, and press the Plus/Start button on your Wii U Gamepad/Wiimote.
8. Start the game of your choosing and play with a GBA!

 

[Ryccardo]

Cool! Or, if you have a GBA flashcard or parallel cable, you can use them instead of the GC/Wii: https://files.extremscorner.org/gamecube/apps/gbi/latest-extra

 

[TotalInsanity4]

fwiw, Sm4sh allows you to natively remap the controls and save it to a profile, so you could play it vanilla

 

[Deleted member 424658]

fwiw, Sm4sh allows you to natively remap the controls and save it to a profile, so you could play it vanilla

The DPad would act as a DPad instead of a stick without HID to VPAD.

 

[TotalInsanity4]

The DPad would act as a DPad instead of a stick without HID to VPAD.

Can you not map controls to the dpad in Smash?

 

[Deleted member 424658]

Can you not map controls to the dpad in Smash?

Not movement. I think you might be able to map attack or something, but no movement. They use DPad for taunts primarily.

 

[pasc]

Wow. Talk about Hype. Wonder if this'll work on the Switch aswell...

 

[KevinLSX]

Wow. Talk about Hype. Wonder if this'll work on the Switch aswell...

Nope

 

[Cloudest]

Wait, this means that we can use pokemon (GBA) through cable link for Pokemon XD/Collosseum in near future? (i hope so) (sorry my broken english though)

 

[Deleted member 424658]

Wait, this means that we can use pokemon (GBA) through cable link for Pokemon XD/Collosseum in near future? (i hope so) (sorry my broken english though)

No. This spoofs the GBA as a Gamecube controller.

 

[Argonitious]

I didn't think this could even be done. Nice find.

I could actually use this for the increasingly common occasion where I need an extra GC controller. I'm too cheap to buy extras right now.

 

[Billy Acuña]

This would be perfect to play GB(C/A) games on RetroArch for Gameboy Player feeling

 

[enarky]

Wow. Talk about Hype. Wonder if this'll work on the Switch aswell...

Nope

Works perfectly fine on my Switch with the original WiiU Gamecube adapter and controller.gba from GBI running on the GBA. Kind of useless since it doesn't emulate all buttons, but it seems to work quite fine.

 

[KevinLSX]

Works perfectly fine on my Switch with the original WiiU Gamecube adapter and controller.gba from GBI running on the GBA. Kind of useless since it doesn't emulate all buttons, but it seems to work quite fine.

But thats different from this technique
Still works though

 

[MikaDubbz]

This is really cool, but I imagine we still can't use the GBA in Nintendont on the Wii U for the games that could link up with the GBA. I bet that simply is impossible, but I so would love it if somehow we could make that work, Four Swords and Crystal Chronicles deserve much more love.

 

[FIX94]

those wii instructions seemed way too complicated for me, so I made a process without the whole mios requirement.
-Grab this little program I just wrote up:
https://github.com/FIX94/gba-link-cable-rom-sender/releases/tag/v1.0
-Put the gbaromsend_wii.dol renamed into sd:/apps/gba-link-cable-rom-sender/boot.dol
-Put controller.gba from gbi into a folder called "gba" on your sd card
-Boot up gba-link-cable-rom-sender with a powered on gba plugged into port 2 of your wii
-Select controller.gba, you can use a gc controller in port 1 or wiimote/classic controller/wiiu pro controller thats player 1 for that selection
-After screen on gba turns white you can then exit gba-link-cable-rom-sender and use it as a gamecube controller

 

[zerofalcon]

With a gba flashcart you only need to run the payload embedded in a compiled gba rom. Extrems made it long time ago. Nice tutorial btw.

 

[Owenge]

Next up we will be using a calculator as a controller for the WiiU

(Tbh this is actual really cool )

 

[doorbell8423]

I have EZflash for GBA SP, GBA to GC link cable, and a hacked wii runing Nintendont through WiiFlow to play GC games.

I played Sonic adventure and tried to transfer chao from SA chao garden to sonic advance tiny chao garden, but its saying No gba is in port 2, but it is, and tiny chao garden is runing on GBA....whats wrong?

Same goes for metroid prime and Zelda four swords...

Thanks!

 

[Deleted member 424658]

I have EZflash for GBA SP, GBA to GC link cable, and a hacked wii runing Nintendont through WiiFlow to play GC games.

I played Sonic adventure and tried to transfer chao from SA chao garden to sonic advance tiny chao garden, but its saying No gba is in port 2, but it is, and tiny chao garden is runing on GBA....whats wrong?

Same goes for metroid prime and Zelda four swords...

Thanks!

You can't use a GBA (as a GBA) with the Gamecube Adapter.