We use the latest available version of Buildroot with slight modifications that allow us to create a truly portable building environment.

Camera hardware is primarily based on the SoC model, image sensor, and sometimes a wireless module. Different cameras may use the same SoC, sensor, and Wi-Fi module, thus requiring similarly built firmware, but still have different GPIO mapping and peripheral configuration.

But these hardware configs have a lot of common, repetitive information related to processor architecture and firmware in general. We use configuration fragments, stored in configs/fragments/*.fragment files, to avoid repeating these settings. You can see how these fragments are included in the module config:

# FRAG: soc toolchain ccache brand rootfs kernel system target

This allows us to minimize the configuration steps required to add new hardware. And, if necessary, we can easily propagate changes to all dependent hardware.

When make is run, the final configuration for a given camera is assembled from the pieces and saved as a ~/output/<camera_config_name>/.config file. It then runs make olddefconfig, which parses the file, resolves any conflicts and redundancies, and creates a new fully populated .config file, saving the previous version as .config.old, which gets overwritten with any new changes, so we also save the initial version of the .config file as .config_original for easier debugging.

To recreate the .config file from the original camera configuration file and its includes, run make defconfig.

We provide a file for local changes to a shared configuration. The local.fragment file in the configs/ directory can contain settings that should be included in a common config on the developer's machine, but don't go into the upstream repository. You can add additional packages there or override the default settings:

BR2_PACKAGE_NANO=y
BR2_PACKAGE_SCREEN=y
BR2_REPRODUCIBLE=n

The local.mk file placed in the root of the firmware directory is a standard Buildroot feature that allows you to override package sources, including those from the Buildroot itself. This is an invaluable feature for local development. Read more about this in chapter 8.13.6 of https://buildroot.org/downloads/manual/manual.html.

LINUX_OVERRIDE_SRCDIR=$(HOME)/dev/thingino/linux
LINUX_HEADERS_OVERRIDE_SRCDIR=$(HOME)/dev/thingino/linux
INGENIC_SDK_OVERRIDE_SRCDIR=$(HOME)/dev/thingino/ingenic-sdk
PRUDYNT_T_OVERRIDE_SRCDIR=$(HOME)/dev/thingino/prudynt-t