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PX4 support for Gemstone is still in the development phase. It runs on the main-domain R5F core, and some peripherals on the board, such as CAN Bus, are not yet available.
PX4 is an open-source autopilot platform for drones and other unmanned vehicles. It provides a complete flight-control stack, from low-level sensor drivers up to vehicle control and mission execution. On the Gemstone board, PX4 runs on the R5F cores on top of NuttX, using the same custom t3-gem-o1 configuration created for the bare NuttX build. Unlike a standalone NuttX build, PX4 vendors both NuttX and its application framework as git submodules. A recursive clone therefore pulls the correct, Gemstone-tuned NuttX automatically, so there is no need to download or build NuttX separately.

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1. Compilation

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1.1. Installing Dependencies and Toolchain

PX4 is compiled with the gcc-arm-none-eabi cross‑compiler for the ARM Cortex‑R5F cores, and its build system additionally relies on a set of Python tools such as kconfiglib, empy and jinja2. On Ubuntu/Debian systems, install the toolchain and the general prerequisites with the package manager:
Because recent Debian/Ubuntu releases restrict system‑wide pip installations, install the Python tools into a virtual environment:
The requirements.txt file lives inside the PX4 source tree, so run the pip install step after downloading the sources (section 1.2). Activate the environment with source ~/px4-venv/bin/activate in every new shell before building.

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1.2. Downloading Source Codes

PX4 references the Gemstone NuttX and NuttX‑apps as git submodules, so the sources are downloaded with a single recursive clone:
The --recursive flag checks out the correct NuttX (the Gemstone px4 branch) and NuttX‑apps into the platforms/nuttx/NuttX directory, so a separate NuttX download is not required. If you cloned without --recursive, fetch the submodules afterwards with git submodule update --init --recursive.

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1.3. Compiling the Project

PX4 builds a specific board target directly, so no separate configuration step is required. With the Python environment from section 1.1 active, compile the Gemstone board image:
This performs a parallel build and produces build/t3gemstone_o1_default/t3gemstone_o1_default.elf (the image loaded onto the R5F core) along with .bin and .px4 files.

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2. Running

Like the bare NuttX image, PX4 runs on the main-domain R5F core and is loaded from Linux or U-Boot using the remoteproc mechanism. While PX4 runs on the R5F core, Linux continues to run on the A53 cores.
To use the remoteproc mechanism in U-Boot, you can refer to the 2.8. Running the Compiled Project in U-Boot section.
Program files to be loaded onto the cores via remoteproc must be copied to the /lib/firmware directory with predefined names. At system startup, the remoteproc mechanism will automatically load the programs onto the relevant cores. Follow the steps below to run PX4 using remoteproc.
  1. Copy the build/t3gemstone_o1_default/t3gemstone_o1_default.elf file resulting from the compilation to the /lib/firmware directory with the name j722s-main-r5f0_0-fw.
  2. Reboot the board.
  3. You can access NuttShell by connecting a USB-to-TTL device to the UART-MAIN1’s GPIO-14 (TX) and GPIO-15 (RX) pins on the 40-pin HAT.
  4. From the opened nsh console you can inspect the running system with commands such as ver all, top, and uorb status.

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3. Using the Sensors

The on‑board InvenSense ICM‑20948, a 9‑axis IMU with an accelerometer, gyroscope and an integrated AK09916 magnetometer, is connected to the R5F over SPI. Start its driver from the nsh console:
Here -s selects the SPI interface, -b 1 the SPI bus, -c 3 the chip‑select, and -M additionally enables the magnetometer. Once the driver is running, you can stream the live sensor data through PX4’s uORB middleware with the listener command:
To observe the overall system, uorb top lists the publication rates of all active topics and work_queue status shows the timing of the driver’s work queue.