GRUB switch

This is a simple physical switch to control GRUB2 inspired by a simplar project for STM32, but implemented on the Raspberry Pi Pico (developed on RP2040-Zero, but any Pico should be good).

The code is using an SPDT On-Off-On switch, one side selects Linux, the other Windows, while in the middle selection, the GRUB menu stays on indefinately - but this should be very easy to modify.

I needed this, because I have a strange dual boot setup where my monitor usually turns on with the input that is not the default from my UEFI setup.

A 3d printable case is also available in the case folder, with Fusion 360 design files.

Build and install

An uf2 binary is available as release for easy testing.

Install the pico-SDK, cmake and arm-eabi-gcc.

Make sure to set the environemnt variable PICO_SDK_PATH to point the folder where your pico-SDK is (e.g. export PICO_SDK_PATH=/usr/share/pico-sdk).

Then continue with the usual cmake setup:

mkdir build
cd build
cmake ..
make

Finally, install the generated build/grubswitch.uf2 on the Pico. It will reboot as a FAT16 drive, labeled "GRUB-SWITCH".

The switch should be connected to pin28 and pin29 if the code is used unmodified.

Setup GRUB

Copy 49_switch to /etc/grub.d. Modify the entry numbers highlighted with comments. Make sure it's executable and run update-grub as root.

Modification

The letters set by the switch are defined in msc_disk.h. The switch is read in main.c. The filesystem and filename are defined in msc_dis.c - although I wouldn't recommend changing this unless you have to.

Inspiration

This project was developed based on the following:

• The ST implementation of the same idea
• Another pico implementation I just didn't like that it's a documentation on how to modify an example
• A nice demonstration project of USB MSC with a lot of links and explanation video.