This flake packages the firmware for the Freedom E310 and the Espressif ESP32 SoCs.
It is currently based against $HEAD of upstream for the source files.
If anything breaks, you can always pin the riscvphone-src input to a working revision:
url = "git://majstor.org/rvPhone.git?rev=38e19a65fda7a37688320b4b732eb1113bbcbad7";
You may find more information about this project here and here.
For further details, please refer to the documentation in the flake itself.
To build the firmware for each SoC (and possibly also flash it), type nix build .#fe310 or nix build .#esp32.
You can enter a developer shell by typing nix develop .#fe310 or nix develop .#esp32.
Navigate into fw/fe310 or fw/esp32 and type make to compile. Typing make clean will delete the compiled files.
When typing make in fw/esp32, a configuration menu will open if no sdkconfig configuration file exists, even if empty. You can manually choose the configuration values in this menu at any time by typing make menuconfig or pass them automatically via the sdkconfig.defaults file.