This implementation builds a FAT12 file system in the Raspberry Pi Pico's onboard flash memory, supporting both file operations from inside the Pico using the FatFs library and from the USB host using the USB Mass storage class.

git submodule update --init
cd lib/pico-sdk; git submodule update --init; cd ../../

mkdir build; cd build
cmake ..
make

Now you have picofs.uf2 and can drag and drop it onto your Raspberry Pi Pico to install and run it.

The main thing.

• flash.c: Read/write Pico onboard flash memory FAT12
• fatfs_driver.c: FatFs driver for Pico onboard flash memory
• usb_msc_driver.c: USB Mass Storage Class driver to Pico onboard flash memory
• bootsel_button.h: Onboard BOOTSEL button readout.
• lib: pico-sdk
• main.c: main

FAT12 does not take concurrent access into account, so concurrent access, including updates from the USB host and PICO, will have unintended consequences; with proper unmounting and mounting operations on the USB host, the files can be manipulated relatively safely. For example, if Pico is in the process of continuously appending temperature data to a file, it will be cached when it is connected to the USB host, and the USB host will not know about the update.

• pico-sdk https://github.com/raspberrypi/pico-sdk
• FatFs http://elm-chan.org/fsw/ff/