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1. Overview

ArduPilot is a mature, feature-rich open-source autopilot system supporting various vehicle types including planes, copters, rovers, and submarines. This guide covers running ArduPilot on T3 Gemstone O1 development boards.

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2. Hardware Specifications

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Inertial Measurement Unit (IMU)

  • Model: InvenSense ICM-20948
  • Interface: SPI

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Magnetometer (Compass)

  • Model: AKM AK09916
  • Interface: Internal (via ICM-20948)
  • External I2C Compass Probing: Enabled

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Barometer

  • Model: Bosch BMP390
  • Interface: SPI

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CAN Bus

  • Transceiver: TCAN1462-Q1
  • Interface: 1x CAN interface available

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Battery Monitor

  • Model: ADS1115
  • Interface: Can be connected externally via I2C-MCU0 at address 0x48
  • Channels: 4-channel 16-bit ADC for voltage/current sensing

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Status Indicators

  • LEDs: Green-red status LEDs
  • Buzzer: Can be connected externally via GPIO-26

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GPS, RC Input & PWM Outputs

  • GPS: Serial communication via UART-MAIN6, external compass via I2C-MCU0
  • RC Input: SBUS communication via UART-MAIN1
  • PWM Outputs: 7x hardware PWM channels accessible from 40-pin GPIO header

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3. Installation

ArduPilot is distributed as a Debian package via the T3 Gemstone APT repository. The package includes pre-compiled binaries for all vehicle types and necessary configuration files. 
gemstone@t3-gem-o1:~$ sudo apt update
gemstone@t3-gem-o1:~$ sudo apt install t3-gem-ardupilot
The installation creates the following directory structure: 
/opt/ardupilot/
├── bin/
│   ├── arducopter
│   ├── arduplane
│   ├── ardurover
│   └── ardusub
├── etc/
│   ├── ardupilot.env
│   └── ardupilot.parm
└── var/
    ├── log/
    ├── storage/
    └── terrain/
If you prefer to compile ArduPilot from source, build instructions are available at github.com/t3gemstone/ardupilot

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3.1. Device-tree Overlays

Before running ArduPilot, you must enable the required device-tree overlays to configure the necessary peripherals. Edit /boot/uEnv.txt and append the following overlays to the overlays= line: 
k3-am67a-t3-gem-o1-spidev0-1cs.dtbo
k3-am67a-t3-gem-o1-i2c1-400000.dtbo
k3-am67a-t3-gem-o1-uart-ttys0.dtbo
k3-am67a-t3-gem-o1-uart-ttys6.dtbo
k3-am67a-t3-gem-o1-pwm-ecap0-gpio12.dtbo
k3-am67a-t3-gem-o1-pwm-ecap1-gpio16.dtbo
k3-am67a-t3-gem-o1-pwm-ecap2-gpio18.dtbo
k3-am67a-t3-gem-o1-pwm-epwm0-gpio5-gpio14.dtbo
k3-am67a-t3-gem-o1-pwm-epwm1-gpio6-gpio13.dtbo
Example /boot/uEnv.txt configuration: 
overlays=k3-am67a-t3-gem-o1-spidev0-1cs.dtbo k3-am67a-t3-gem-o1-i2c1-400000.dtbo k3-am67a-t3-gem-o1-uart-ttys0.dtbo k3-am67a-t3-gem-o1-uart-ttys6.dtbo k3-am67a-t3-gem-o1-pwm-ecap0-gpio12.dtbo k3-am67a-t3-gem-o1-pwm-ecap1-gpio16.dtbo k3-am67a-t3-gem-o1-pwm-ecap2-gpio18.dtbo k3-am67a-t3-gem-o1-pwm-epwm0-gpio5-gpio14.dtbo k3-am67a-t3-gem-o1-pwm-epwm1-gpio6-gpio13.dtbo
Reboot the board for the changes to take effect: 
gemstone@t3-gem-o1:~$ sudo reboot

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3.2. Systemd Service Management

Each ArduPilot vehicle type has its own systemd service:
  • arducopter.service - Multirotor copters
  • arduplane.service - Fixed-wing aircraft
  • ardurover.service - Ground vehicles
  • ardusub.service - Underwater vehicles
Only one vehicle service can be enabled at a time as they conflict with each other.

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3.2.1. Starting a Vehicle

To run ArduPilot for your vehicle type, enable and start the corresponding service: 
# For copters
gemstone@t3-gem-o1:~$ sudo systemctl enable arducopter.service
gemstone@t3-gem-o1:~$ sudo systemctl start arducopter.service

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3.2.2. Switching Vehicle Types

To switch to a different vehicle type, first disable the current service: 
# Disable current vehicle
gemstone@t3-gem-o1:~$ sudo systemctl disable arducopter.service
gemstone@t3-gem-o1:~$ sudo systemctl stop arducopter.service

# Enable new vehicle
gemstone@t3-gem-o1:~$ sudo systemctl enable arduplane.service
gemstone@t3-gem-o1:~$ sudo systemctl start arduplane.service

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3.2.3. System Configuration Service

The ardupilot-sysconfig.service is a oneshot service that prepares the board for running ArduPilot by configuring GPIO pins and other peripherals. This service runs automatically when any vehicle service is enabled and does not need manual intervention.

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3.2.4. Checking Service Status

Monitor the ArduPilot service status and logs: 
# Check service status
gemstone@t3-gem-o1:~$ sudo systemctl status arducopter.service

# View real-time logs
gemstone@t3-gem-o1:~$ sudo journalctl -u arducopter.service -f

# View recent logs
gemstone@t3-gem-o1:~$ sudo journalctl -u arducopter.service -r

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4. Configuration

After modifying configuration files, restart the ArduPilot service for changes to take effect:
gemstone@t3-gem-o1:~$ sudo systemctl restart arducopter.service

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4.1. ArduPilot Startup Options

/opt/ardupilot/etc/ardupilot.env file defines command-line arguments for ArduPilot, including serial port configuration, directory paths, and performance options. Serial Port Configuration: 
# USB Gadget Ethernet - MAVLink2 (Default)
SERIAL0=--serial0 udp:192.168.7.255:14550:bcast

# Telemetry UART 57600 Baud, MAVLink 1
SERIAL1=--serial1 /dev/ttyS0

# GPS UART 230400 Baud
SERIAL3=--serial3 /dev/ttyS6

# SBUS RC Input UART 100000 Baud
SERIAL5=--serial5 /dev/ttyS3
Uncomment and configure additional serial ports as needed. Additional information about serial ports can be found in ArduPilot’s documentation. Directory Paths (Optional): 
LOG_DIRECTORY=--log-directory /opt/ardupilot/var/log
TERRAIN_DIRECTORY=--terrain-directory /opt/ardupilot/var/terrain
STORAGE_DIRECTORY=--storage-directory /opt/ardupilot/var/storage
MODULE_DIRECTORY=--module-directory /usr/lib/ardupilot/modules

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4.2. ArduPilot Parameters

/opt/ardupilot/etc/ardupilot.parm file defines default parameters loaded on startup. 
# Setup SERIAL5 as SBUS RC input
SERIAL5_PROTOCOL,23
SERIAL5_BAUD,100
Additional parameters can be added following ArduPilot’s documentation.

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4.3. CPU Isolation for Real-Time Performance

Linux supports isolating CPU cores from the kernel process scheduler. This allows ArduPilot to run on dedicated cores without interference from non-real-time processes, improving latency and jitter characteristics. To isolate cores 2 and 3 for ArduPilot:
  1. Edit kernel boot parameters Open /boot/uEnv.txt and add isolcpus=2,3 to the kernel arguments: 
    args_mmc=setenv bootargs isolcpus=2,3 console=${console} ...
  2. Configure CPU affinity Edit /opt/ardupilot/etc/ardupilot.env and uncomment the CPU_AFFINITY line: 
    CPU_AFFINITY=--cpu-affinity 2,3
  3. Reboot the board 
    gemstone@t3-gem-o1:~$ sudo reboot
After reboot, ArduPilot will run exclusively on cores 2 and 3, while system processes use cores 0 and 1.

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5. Usage

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5.1. Board Orientation

Mount the board in your vehicle with the GemStone logo pointing toward the front of the vehicle. This ensures proper sensor orientation and coordinate system alignment.

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5.2. Status LEDs

The green-red status LEDs located near CSI/DSI ports indicate the flight controller’s current state. Refer to ArduPilot’s documentation for detailed LED patterns and their meanings.

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5.3. Flight Logs

ArduPilot stores flight logs in /opt/ardupilot/var/log/ using the binary BIN format. Logs are automatically rotated, with LASTLOG.TXT indicating the most recent log number. These logs can be analyzed using UAV Log Viewer.

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5.4. Peripherals

The 40-pin GPIO header provides access to peripherals, PWM outputs, and communication interfaces.

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5.4.1. GPIO Pinout

The following table shows the function of each pin in the GPIO header after applying device-tree overlays. The table assumes the board is oriented so that you can see the GemStone logo upright.
3v3 Power3v3 Power5v Power5v Power
I2C-MCU0 SDA (GPS, ADS1115)GPIO-25v Power5v Power
I2C-MCU0 SCL (GPS, ADS1115)GPIO-3GNDGND
UART-MAIN6 RX (GPS)GPIO-4GPIO-14PWM-0B (RCOut-2)
GNDGNDGPIO-15UART-MAIN1 RX (RCIn SBUS)
UART-MAIN6 TX (GPS)GPIO-17GPIO-18PWM-ECAP2 (RCOut-7)
GPIO-27GNDGND
GPIO-22GPIO-23
3v3 Power3v3 PowerGPIO-24UART-WKUP0 TX (Telemetry)
SPI-MCU0 MOSIGPIO-10GNDGND
SPI-MCU0 MISOGPIO-9GPIO-25
SPI-MCU0 SCLKGPIO-11GPIO-8SPI-MCU0 CS0
GNDGNDGPIO-7UART-WKUP0 RX (Telemetry)
I2C-WKUP0 SDA (Reserved)GPIO-0GPIO-1I2C-WKUP0 SCL (Reserved)
PWM-0A (RCOut-1)GPIO-5GNDGND
PWM-1A (RCOut-3)GPIO-6GPIO-12PWM-ECAP0 (RCOut-5)
PWM-1B (RCOut-4)GPIO-13GNDGND
GPIO-19GPIO-16PWM-ECAP1 (RCOut-6)
BuzzerGPIO-26GPIO-20
GNDGNDGPIO-21

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5.4.2. Device Paths

Linux device paths for each peripheral:
UART-WKUP0/dev/ttyS0
UART-MAIN1/dev/ttyS3
UART-MAIN6/dev/ttyS6
I2C-MCU0/dev/i2c-1
SPI-MCU0 CS0/dev/spidev0.0
PWM-0A/sys/class/pwm/pwmchip3/pwm0
PWM-0B/sys/class/pwm/pwmchip3/pwm1
PWM-1A/sys/class/pwm/pwmchip5/pwm0
PWM-1B/sys/class/pwm/pwmchip5/pwm1
PWM-ECAP0/sys/class/pwm/pwmchip0/pwm0
PWM-ECAP1/sys/class/pwm/pwmchip1/pwm0
PWM-ECAP2/sys/class/pwm/pwmchip2/pwm0

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5.4.3. RC Input

The board supports RC input via the SBUS protocol through the UART-MAIN1 RX (GPIO-15) pin. SBUS is a widely used digital RC protocol that provides reliable communication between your RC receiver and the flight controller.
5.4.3.1. Signal Inversion Requirement
SBUS protocol uses an inverted serial signal, which means you must use an external signal inverter circuit between your SBUS receiver and the UART-MAIN1 RX pin. Without this inverter, the board will not be able to read SBUS data correctly. To build the signal inverter circuit, you will need:
  • 1x NPN transistor (e.g., S9014 TO-92 package)
  • 1x 10kΩ resistor
  • 1x 1kΩ resistor

Signal Inverter Circuit

Connection Details:
  • SBUS receiver output connects through the 1kΩ resistor to the transistor base
  • Transistor collector connects to UART-MAIN1 RX pin (GPIO-15)
  • 10kΩ pull-up resistor connects between collector and 3v3 VCC
  • Transistor emitter connects to GND

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5.5. QGroundControl Connection

QGroundControl (QGC) is the recommended ground control station for ArduPilot. You can connect via UDP or serial telemetry.

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5.5.1. USB-Ethernet Connection (Default)

Connect the Gemstone board to your PC via USB Type-C cable. The board uses USB Gadget API to provide Ethernet-over-USB with automatic IP configuration:
  • Board IP: 192.168.7.2
  • PC IP: Assigned via DHCP (typically 192.168.7.59)
  • MAVLink Port: UDP broadcast at 192.168.7.255:14550
QGC will automatically detect and connect to the vehicle if UDP autoconnect is enabled (default setting).

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5.5.2. Serial Telemetry Connection

For wireless telemetry using radio modules:
  1. Connect telemetry radio to Gemstone board
    • Connect telemetry module to board’s UART-WKUP0 pins
  2. Connect telemetry radio to PC
    • Insert the second radio module to your PC via USB-to-TTL device
    • Note the created TTY device (e.g., /dev/ttyUSB0)
  3. Configure QGroundControl
    • Open Application Settings → Comm Links
    • Click Add button
    • Select the correct serial port and 57600 baud rate
    • Save configuration and click Connect button
MAVLink messages should now arrive, and you should see the vehicle’s status in QGC.

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6. Troubleshooting

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6.1. ArduPilot Service Won’t Start

Check service status and logs: 
gemstone@t3-gem-o1:~$ sudo systemctl status arducopter.service
gemstone@t3-gem-o1:~$ sudo journalctl -u arducopter.service -r
Verify network configuration from PC: 
ubuntu@host:~$ ping 192.168.7.2
Check if ArduPilot is running and broadcasting from Gemstone board: 
gemstone@t3-gem-o1:~$ sudo netstat -u -n | grep 14550
Ensure QGC UDP autoconnect is enabled in Application Settings.

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6.3. GPS Not Detected

GPS should be connected to UART-MAIN6 (GPIO-4 and GPIO-17) and I2C-MCU0 (pins GPIO-2 and GPIO-3). Check GPS connection on GPIO header pins and verify configuration: 
gemstone@t3-gem-o1:~$ cat /opt/ardupilot/etc/ardupilot.env | grep SERIAL3

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6.4. PWM Outputs or Serial Ports Not Working

Verify device-tree overlays are loaded: 
gemstone@t3-gem-o1:~$ ls /proc/device-tree/chosen/overlays
You should see names listed in Device-tree Overlays. If some overlays are missing, check /boot/uEnv.txt configuration and reboot the board.