Ixox/preenfm2 is the official repository of the preenfm2 firmware.
You can find here the compiled firmware, its code source and some hardware files for the PCB, MCU board and cases.
To flash the preenfm2 for the first time, follow these instructions
To compile the firmware, you'll need arm-gcc version 4.7
Add the bin directory to your PATH, and run 'make', you'll get the list of the available targets.
$ make
You must chose a target
Don't forget to clean between different build targets
clean : clean build directory
pfm : build pfm2 firmware
pfmcv : build pfm2 firmware for Eurorack
installdfu : flash last compiled firmware through DFU
zip : create zip with all inside
Since some refactoring, the bootloader does not compile anymore. But it's available in its binary format.
Then put your preenfm2 in bootloader mode. Look at DFU part 4.
To flash the firmware on the preenfm2 using the DFU protocol :
make installdfu
Once it's done, unplug the power cable and plug it back.
Many effects have been added in the firmware 2.11. They were coded by Toltekradiation.
His github repo is here. You'll find there some description of the different effects.