UF2 Loader is a custom bootloader for the RP2040 and RP2350 on the PicoCalc. With UF2 Loader installed, applications can be loaded directly from the SD card at will without needing to plug into a PC.
Clone the source code and initialize the submodules.
git clone https://github.com/pelrun/uf2loader.git
cd uf2loader
git submodule update --init --recursiveBuild the bootloader.
PICO_SDK_PATH=/path/to/pico-sdk cmake -DPICO_BOARD=pico -B build -S .
cd build
make -j8The compiled binaries will be placed in the output/ folder.
Copy BOOT2040.UF2 (for Pico/Pico W) or BOOT2350.UF2 (for Pico 2/2W) to the root of the Picocalc SD card. This is the menu UI and is loaded by the bootloader when needed.
Create pico1-apps (for Pico/Pico W) or pico2-apps (for Pico 2/2W) folders on the SD card and copy any UF2 files you want to use to them.
Pico 1 and Pico 2 files can coexist on the SD card simultaneously.
Flash bootloader_pico.uf2 (for Pico/Pico W) or bootloader_pico2.uf2 (Pico 2/2W) to your Pico using BOOTSEL mode or Picotool.
If an application is already present in flash, by default it will be started immediately on power-on.
Hold Up, F1 or F5 during power-on to launch the loader menu.
If an application is present, the first item in the menu (in [square brackets]) will launch it. If the application has the appropriate Binary Information block then the name of the application will be shown here.
Hold Down or F3 during power-on to put the Pico into BOOTSEL mode.
If the menu cannot be loaded for any reason (no SD card, BOOTnnnn.UF2 not found, aliens etc) then the device will fall into BOOTSEL mode.
On the RP2350 only, UF2 files can also be written to the Pico in BOOTSEL mode or via Picotool as normal and will automatically be placed in the app partition.
On the RP2040, the top 16k of flash is occupied and must not be overwritten by the application. 8k is for the bootloader, and 8k is used by the bluetooth stack on the W.
As the RP2040 does not have a mechanism for write protecting flash regions, the application has to manually avoid flashing this area, and so the bootloader stores some information in the application vector table for use by the developer to know how much free flash space is available in place of the PICO_FLASH_SIZE_BYTES macro.
If the magic number (0xe98cc638) is present at XIP_BASE+0x110, then the word at XIP_BASE+0x114 is the size of the safe flash area. The application is free to erase or reflash any addresses below this without affecting the bootloader.
On the RP2350, a flash partition is used, and the application can't directly overwrite (or even see) the bootloader in the normal case (please use RP2350's rom_flash_op instead of the old flash_range_erase/flash_range_program apis, which do not care about the partition table.) The application can get the size of the partition via the bootrom API. (see bl_app_partition_get_info() in proginfo.c for an implementation.)
- Hiroyuki Oyama: Special thanks for the firmware loader mechanism and VFS file system.
- TheKiwil: Special thanks for contributions on supporting pico2 boards with new custom linker script.
- muzkr: Special thanks for the original boot2/high-mem implementation
- adwuard: Special thanks for the original Picocalc SD Boot application that UF2 Loader is heavily based on.
- cuu: Various UI improvements taken from their SD Boot fork
- nipo: Pico Binary Information parser library
- Elm-ChaN: because everyone uses their FatFS and Petit FatFS libraries. E. v. e. r. y. o. n. e.
- Forum Page and Discussion: Clockwork Pi Forum