In ChromiumOS, the hps-firmware package builds all the firmware binaries needed to run HPS on a Chromebook: FPGA bitstream, FPGA application, and MCU application. The hps-firmware-tools package builds additional tools which are useful for development and testing, for example the hps-factory program. The hps-firmware package is included in the ChromiumOS base image, whereas the hps-firmware-tools package is only included in test/dev images.
You can use normal ChromiumOS workflows to work on these packages (see the relevant section of the ChromiumOS Developer Guide). For example:
cros workon --board=brya start hps-firmware FEATURES=test emerge-brya hps-firmware
However, sometimes it’s more convenient to build individual pieces of the HPS firmware while you’re working on it. The scripts/ subdirectory contains some helper scripts for this purpose. These helper scripts must be run inside the ChromiumOS chroot.
scripts/build-fpga-bitstream
Synthesises the FPGA gateware into a bitstream, suitable to be programmed onto the SPI flash and loaded by the FPGA.
scripts/build-fpga-rom
Builds the Rust code for the FPGA application and emits a raw image, suitable to be programmed onto the SPI flash and executed by the soft CPU in the FPGA. We sometimes call this the “FPGA ROM” image, because the soft CPU is configured to execute from a read-only memory.
scripts/build-fpga-rom-dev
As above, but builds the Rust code with development features enabled. These are extra features which are never included in release firmware, such as image capturing support (see Capturing images).
You can use the images built the above scripts as inputs for scripts/proto2-mon. See Working with proto2.
Rust code in HPS firmware follows the normal Rust conventions for unit testing. Rust unit tests are executed in the test phase of the hps-firmware ebuild.
You can also run them outside the ebuild by using the scripts/run-tests helper script.