PX4 HITL Simulink Monitor & Tune (External Mode over XCP Serial) fails to connect on Cube Orange Plus while normal deployment works

I am working on the MathWorks example “PX4 Autopilot in Hardware-in-the-Loop (HITL) Simulation with UAV Dynamics in Simulink” using real PX4 hardware.

Hardware & setup

• Flight controller: Cube Orange Plus
• Host OS: Windows
• PX4 firmware: PX4-Autopilot (HITL enabled)
• Simulink version: R2024b
• Communication:
• USB-TTL (FTDI) connected to the Cube (TELEM/UART)
• MAVLink over USB/UDP for QGroundControl
• Wiring verified and matches the example
• COM port detected correctly in Windows Device Manager

What works (Method 1)

✔ Controller deployed to the autopilot in normal mode (no Monitor & Tune / no External Mode)

✔ HITL simulation runs correctly

✔ QGroundControl receives MAVLink data and vehicle behaves as expected

What does NOT work (Method 2 – Monitor & Tune)

When deploying the controller for Monitor & Tune (External Mode using XCP on Serial), the connection fails.

Notes

• I followed the example step-by-step exactly as documented.
• The same serial port (COM16) works for normal deployment.
• No other application (PuTTY, QGC, etc.) is using COM16 during Monitor & Tune.
• Baud rate is set to 921600 as required by the example.
• The issue appears only when enabling External Mode (XCP on Serial).

Question

• Is there a known limitation or additional PX4 configuration required for External Mode (XCP on Serial) with Cube Orange Plus?
• Is this issue related to PX4 firmware, serial port assignment, or Windows serial driver behavior?
• Has anyone successfully used Monitor & Tune with PX4 HITL on real hardware (Cube / Pixhawk series)?

action: EXT_INIT
Creating Target Handler (XCP on Serial)...
Build directory:
C:\Users\Rahul\OneDrive - BLUJ AEROSPACE PRIVATE LIMITED\Documents\MATLAB\Examples\R2024b\px4\PX4HITLSimulinkPlant2\px4demo_HITLSimulinkPlant\work\code\Quadcopter_ControllerWithNavigation_ert_rtw

Serial Port Name: COM16
Baud Rate: 921600

action: EXT_CONNECT
Connecting to the target...
External Mode Open Protocol Connect command failed

Caused by:
Could not connect to target application:
XCP serial port error: open: The system cannot find the file specified
[system:2 at
\\mathworks\hub\3rdparty\R2024b\11242549\win64\boost\include\boost-1_81\
boost\asio\detail\impl\win_iocp_serial_port_service.ipp:66:5
in function 'open']

Component: Simulink
Category: Model error

Answer 1

[Arun Mathamkode]

Use GPS2 or GPS1 for monitor and tune communication over non-USB port connection, as there might be issues using TELEM1 or TELEM2 ports for Cube Orange/Cube Blue H7/ Cube Orange Plus. Deployment on Cube Orange Autopilot from Simulink - MATLAB & Simulink. For the GPS1 and GPS2 ports, make sure that GPS_1_CONFIG or GPS_2_CONFIG are not assigned to those ports, ensuring that PX4 does not start any GPS protocol on them.