Since the confirmation has been made that the RP2040, a $3 microcontroller, can be used to hack the Nintendo Switch, news are pouring daily from folks on the scene helping to make the modding process easier. One of the interesting ideas that’s coming our way is from GBATemp member Saliciae, who’s building a modified RP2040 board that will fit inside the Switch. Even better, the hacker promises to release the specs of the board under a Creative Commons license.

What is McFly for the Nintendo Switch?

McFly is a work in progress microcontroller based on the RP2040, that integrates what’s necessary to use the RP2040 for a Nintendo Switch hack, while removing “unnecessary” parts of the original RP2040 Zero, to make the design fit inside a Nintendo Switch. One of the particularities of the McFly is that once you’re done flashing it, you have to “snap” the USB part out of it, so that it will fit nicely inside the case of the Switch (if you ever need to re-flash the device, the two parts of the board are designed to be reconnected either via solder or a pin header)

Saliciae doesn’t plan to actually manufacture or distribute the board, only to provide the design for it, for other people to manufacture the result.

Although the design tries to cram as much as possible inside the tiny space, the MOSFET and/or flat cable will still be required: the MOSFET needs to be as close as possible to the caps and in the current design cannot be integrated too close to the RP2040 Board.

From Siliciae:

Introducing the Mcfly, a barebones RP2040 board designed from the ground up to be compact, simple and slim. With a USB port that breaks away after initial programming the overall thickness of the board can be reduced to ~2mm. An X and Y footprint of ~19x19mm makes this stripped back board suitable for internal installation in the switch. No stone was left unturned in the design of this board, with all the features of a conventional picofly install present including the debug WS2812 LED and the jumper to reset the glitch timings as well as the inclusion of a 6 pin fpc connector designed to be used with HWFLY CPU flex cables, simplifying the installation and reducing the risk of damaging the APU. Despite the breakaway connector the Mcfly can be updated too, using a 5 pin 1.27mm header the usb section can be either temporarily soldered back on, or a pin header attached and it held in place whilst the board is reprogrammed. 

Upon completion of testing the Mcfly will be released under the Creative Commons Attribution Share Alike licence, opening the door for design improvements and alterations by the community, as well as commercialisation by a third party, at this moment i do not plan to commercialise this design myself, I simply dont have the time to sell these personally. If you would be interested in selling these or know someone who is please get in touch! 

How does this solution compete against a regular RP2040 Zero, or HWFly RP2040 which are already being sold?

There are now multiple solutions to install a picofly on the Nintendo Switch. From a hardware perspective, probably the most “elegant” ones for now are the HWFly RP2040 which can already be found on some resellers. From screenshots, those seem to be missing a USB connection however (most likely so that the chip can fit inside the Switch), so I assume they cannot be reflashed, and this means you’ll be “stuck” with a non open source solution. Possibly not a big deal for most users.

From Saliciae:

This wont be price competitive with a 2040-Zero, in low quantities that’s simply not possible, nor will it be as easy to install as the inevitable HwFly picofly board. The goal is for this to be a community driven open source solution that simplifies the install to the greatest extent possible whilst still being reasonably low cost, using off the shelf parts you can get from any component retailer

Source: Saliciae on GBATemp