If you want to test your firmware changes on real HPS hardware, the easiest way is to use an HPS proto2 board. See Working with HPS proto2. But sometimes it's necessary to test your changes on a full ChromeOS device, for example to evaluate how a new model performs under realistic conditions.
Follow these steps:
Turn off write protect.
You must enter developer mode and turn off the system-wide hardware write protect (WP) signal. It is not possible to run unsigned HPS firmware unless WP is turned off.
Recent ChromeOS devices support case-closed debugging (CCD). Use a Suzy-Q cable or ServoV4 to open the CCD interface and turn off WP. See the Case Closed Debugging documentation.
Note that this makes the device insecure and thus it should not be used as a normal ChromeOS device (do not log in with a real user account).
Build the firmware with your changes.
You can build the complete hps-firmware package, for example:
cros workon --board=brya start hps-firmware emerge-brya hps-firmware
You can also build individual images outside the ebuild. See Developing outside the ebuild.
Manually copy firmware to the DUT.
The usual cros deploy workflow is not usable in this scenario, because the filesystem paths do not match:
hps-firmware builds firmware from source and installs to /firmware/hps, which does not exist in the ChromeOS disk image.
hps-firmare-images copies pre-built signed firmware into /usr/lib/firmware/hps, which is loaded at runtime by hpsd.
Instead, copy the firmware to the correct location on the DUT filesystem. For example:
scp /build/brya/firmware/hps/fpga_application.bin \
/build/brya/firmware/hps/fpga_bitstream.bin \
/build/brya/firmware/hps/mcu_stage1.bin \
/build/brya/firmware/hps/mcu_stage1.version.txt \
$DUT:/usr/lib/firmware/hps/
On the DUT, compress the images so that they have the expected names:
ssh $DUT rm /usr/lib/firmware/hps/*.bin.xz ssh $DUT xz /usr/lib/firmware/hps/*.bin
Restart hpsd to load the firmware.
On the DUT, run restart hpsd. Monitor /var/log/messages to confirm that hpsd successfully loaded and started your unsigned firmware.