Added project

.gitignore

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+build
+.vscode

49_switch

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+#! /bin/sh
+exec tail -n +3 ${0}
+# Look for hardware switch device by its hard-coded filesystem ID
+search --no-floppy --label --set hdswitch GRUB-SWITCH
+
+# If found, read dynamic config file and select appropriate entry for each position
+if [ "${hdswitch}" ] ; then
+  source ($hdswitch)/switch.cfg
+
+  if [ "${os_hw_switch}" == "l" ] ; then
+    # Boot Linux
+    set default="0" #change this to your Linux entry number
+    set timeout=0
+  elif [ "${os_hw_switch}" == "w" ] ; then
+    # Boot Windows
+    set default="2" #change this to your windows entry number
+    set timeout=0
+  elif [ "${os_hw_switch}" == "s" ] ; then
+    # default with infinite timeout
+    set default="${GRUB_DEFAULT}"
+    set timeout=-1
+  else
+    # Fallback to default
+    set default="${GRUB_DEFAULT}"
+    set timeout="${GRUB_TIMEOUT}"
+  fi
+fi

CMakeLists.txt

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+cmake_minimum_required(VERSION 3.13...3.27)
+
+set(PROJECT_NAME grubswitch)
+
+
+#pull in the PICO SDK
+include($ENV{PICO_SDK_PATH}/external/pico_sdk_import.cmake)
+
+project(${PROJECT_NAME} C CXX ASM)
+set(CMAKE_C_STANDARD 11)
+set(CMAKE_CXX_STANDARD 17)
+
+set(PICO_EXAMPLES_PATH ${PROJECT_SOURCE_DIR})
+
+#init the sdk
+pico_sdk_init()
+
+add_executable(${PROJECT_NAME}
+        src/main.c
+        src/msc_disk.c
+        src/usb_descriptors.c
+        )
+
+target_include_directories(${PROJECT_NAME} PRIVATE
+        src/)
+
+#pull in pico_stdlib
+target_link_libraries(${PROJECT_NAME} pico_stdlib tinyusb_device)
+
+# pico_enable_stdio_usb(${PROJECT_NAME} 0)
+# pico_enable_stdio_uart(${PROJECT_NAME} 1)
+
+#create uf2
+pico_add_extra_outputs(${PROJECT_NAME})

README.md

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+# GRUB switch
+
+This is a simple physical switch to control GRUB2 inspired by a [simplar project
+for STM32](https://github.com/stecman/hw-boot-selection), 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.
+
+## Build and install
+
+An uf2 binary is available as release for easy testing.
+
+Install the [pico-SDK](https://github.com/raspberrypi/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:
+
+```bash
+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](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](src/msc_disk.h). The
+switch is read in [main.c](src/main.c). The filesystem and filename are defined
+in [msc_dis.c](src/msc_disk.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](https://github.com/stecman/hw-boot-selection)
+* [Another pico
+  implementation](https://www.hackster.io/Madrajib/hardware-boot-select-switch-using-pico-a3e3d5)
+  I just didn't like that it's a documentation on how to modify an example
+* [A nice demonstration project of USB
+  MSC](https://github.com/brendena/pico_drag_n_drop_programmer) with a lot of
+  links and explanation video.

src/main.c

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+#include "tusb.h"
+#include "pico/stdlib.h"
+#include "msc_disk.h"
+
+#define GPIO_LINUX 28
+#define GPIO_WINDOWS 29
+
+/*------------- MAIN -------------*/
+int main(void)
+{
+
+  // init device stack on configured roothub port
+  tusb_init();
+
+  gpio_init(GPIO_LINUX);
+  gpio_init(GPIO_WINDOWS);
+  gpio_set_dir(GPIO_LINUX, false);
+  gpio_set_dir(GPIO_WINDOWS, false);
+  gpio_pull_up(GPIO_LINUX);
+  gpio_pull_up(GPIO_WINDOWS);
+
+
+  while (1)
+  {
+    tud_task(); // tinyusb device task
+
+    if ( !gpio_get(GPIO_LINUX) && !gpio_get(GPIO_WINDOWS)){
+      setSwitchValue(CONFIG_DEFAULT);
+    } else if ( !gpio_get(GPIO_LINUX)){
+      setSwitchValue(CONFIG_LINUX);
+    } else if ( !gpio_get(GPIO_WINDOWS)){
+      setSwitchValue(CONFIG_WINDOWS);
+    } else { //neither are pulled down, switch in the middle
+      setSwitchValue(CONFIG_STOP);
+    }
+  }
+
+  return 0;
+}
+
+//--------------------------------------------------------------------+
+// Device callbacks
+//--------------------------------------------------------------------+
+
+// Invoked when device is mounted
+void tud_mount_cb(void)
+{
+}
+
+// Invoked when device is unmounted
+void tud_umount_cb(void)
+{
+}
+
+// Invoked when usb bus is suspended
+// remote_wakeup_en : if host allow us  to perform remote wakeup
+// Within 7ms, device must draw an average of current less than 2.5 mA from bus
+void tud_suspend_cb(bool remote_wakeup_en)
+{
+  (void) remote_wakeup_en;
+}
+
+// Invoked when usb bus is resumed
+void tud_resume_cb(void)
+{
+}