AP_Periph: Serial passthrough issue

Rex_Taiphoon · March 20, 2026, 3:40am

I am developing a custom CAN-based GPS module using a u-blox F10 and AP_Periph (v1.9.18). I am trying to enable the Serial Passthrough feature so I can connect the GPS to u-center via a secondary UART port, but I’m running into some issues.

Hardware Setup:

Serial1 (USART1): Connected to a UART-to-USB adapter (to PC).
Serial2 (USART2): Connected to the u-blox F10 GPS module.
Firmware: AP_Periph v1.9.18.
- CAN Node information:

Goal: I want to use the DroneCAN page in Mission Planner to configure a serial passthrough. The objective is to route the Serial2 (GPS) data to Serial1, allowing me to access the F10 raw data directly in u-center through my USB adapter.

I followed the documentation and issue below:

github.com/ArduPilot/ardupilot

Serial passthrough does not work for serial ports configured to "GPS" with GPS protocol set to ublox

opened 08:01PM - 25 Apr 21 UTC

closed 11:06AM - 01 Jun 21 UTC

Sebbb

## Bug report **Issue details** Serial passthrough does not work for seria…l ports configured to "GPS" with GPS protocol set to ublox With the settings SERIAL3_PROTOCOL = 5 GPS_TYPE=2 SERIAL_PASS1=8 SERIAL_PASS2=3 I only receive a few packets every 10 seconds After setting SERIAL3_PROTOCOL = -1 and rebooting it's working fine. **Version** 4.1-dev **Platform** [X] All [ ] AntennaTracker [ ] Copter [ ] Plane [ ] Rover [ ] Submarine (tested only with Copter, probably affecting other platforms as well) **Airframe type** irrelevant **Hardware type** Matek H743 **Logs** output of u-center packet console, where you should see packets all the time, however, there are big gaps between the time stamps 19:56:49 R -> UBX NAV-PVT, Size 100, 'Navigation PVT Solution' 19:56:49 R -> UBX NAV-DOP, Size 26, 'Dilution of Precision' 19:56:49 R -> UBX NAV-PVT, Size 100, 'Navigation PVT Solution' 19:56:49 R -> UBX NAV-DOP, Size 26, 'Dilution of Precision' 19:56:49 R -> UBX NAV-PVT, Size 100, 'Navigation PVT Solution' 19:56:49 R -> UBX NAV-DOP, Size 26, 'Dilution of Precision' 19:56:49 R -> UNKNOWN ???, Size 359, 'UNKNOWN' 19:56:49 R <- UBX MON, Size 8, 'Monitor' 19:56:58 R -> UBX NAV-PVT, Size 100, 'Navigation PVT Solution' 19:56:58 R <- UBX MON, Size 8, 'Monitor' 19:56:58 R -> UBX NAV-DOP, Size 26, 'Dilution of Precision' 19:56:58 R -> UBX MON-VER, Size 228, 'Version' 19:56:58 R -> UBX MON-VER, Size 228, 'Version' 19:56:58 R -> UBX NAV-PVT, Size 100, 'Navigation PVT Solution' 19:56:58 R -> UBX NAV-DOP, Size 26, 'Dilution of Precision' 19:56:58 R -> UBX MON-HW, Size 68, 'Hardware Status' 19:56:58 R -> UBX MON-HW2, Size 36, 'Extended Hardware Status' 19:56:58 R -> UBX NAV-PVT, Size 100, 'Navigation PVT Solution' 19:56:58 R -> UBX NAV-DOP, Size 26, 'Dilution of Precision' 19:56:58 R -> UBX NAV-TIMEGPS, Size 24, 'GPS System Time' 19:56:58 R -> UBX NAV-PVT, Size 100, 'Navigation PVT Solution' 19:56:58 R -> UBX NAV-DOP, Size 26, 'Dilution of Precision' 19:56:59 R -> UBX NAV-PVT, Size 100, 'Navigation PVT Solution' 19:56:59 R -> UBX NAV-DOP, Size 26, 'Dilution of Precision' 19:56:59 R -> UBX NAV-PVT, Size 100, 'Navigation PVT Solution' 19:56:59 R -> UBX NAV-DOP, Size 26, 'Dilution of Precision' 19:56:59 R -> UNKNOWN ???, Size 377, 'UNKNOWN' 19:56:59 R <- UBX MON, Size 8, 'Monitor' 19:57:07 R -> UBX NAV-PVT, Size 100, 'Navigation PVT Solution' 19:57:07 R <- UBX MON, Size 8, 'Monitor' 19:57:07 R -> UBX NAV-DOP, Size 26, 'Dilution of Precision' 19:57:07 R -> UBX MON-VER, Size 228, 'Version' 19:57:07 R -> UBX MON-VER, Size 228, 'Version' 19:57:08 R -> UBX NAV-PVT, Size 100, 'Navigation PVT Solution' 19:57:08 R -> UBX NAV-DOP, Size 26, 'Dilution of Precision' 19:57:08 R -> UBX NAV-PVT, Size 100, 'Navigation PVT Solution' 19:57:08 R -> UBX NAV-DOP, Size 26, 'Dilution of Precision' 19:57:08 R -> UBX NAV-PVT, Size 100, 'Navigation PVT Solution' 19:57:08 R -> UBX NAV-DOP, Size 26, 'Dilution of Precision' 19:57:08 R -> UBX MON-HW, Size 68, 'Hardware Status' 19:57:08 R -> UBX MON-HW2, Size 36, 'Extended Hardware Status' 19:57:08 R -> UBX NAV-PVT, Size 100, 'Navigation PVT Solution' 19:57:08 R -> UBX NAV-DOP, Size 26, 'Dilution of Precision' 19:57:08 R -> UBX NAV-TIMEGPS, Size 24, 'GPS System Time' 19:57:08 R -> UBX NAV-PVT, Size 100, 'Navigation PVT Solution' 19:57:08 R -> UBX NAV-DOP, Size 26, 'Dilution of Precision' 19:57:08 R -> UNKNOWN ???, Size 481, 'UNKNOWN' 19:57:08 R <- UBX MON, Size 8, 'Monitor' 19:57:17 R -> UBX NAV-PVT, Size 100, 'Navigation PVT Solution' 19:57:17 R <- UBX MON, Size 8, 'Monitor' 19:57:17 R -> UBX NAV-DOP, Size 26, 'Dilution of Precision' 19:57:17 R -> UBX NAV-TIMEGPS, Size 24, 'GPS System Time' 19:57:17 R -> UBX MON-VER, Size 228, 'Version' 19:57:17 R -> UBX MON-VER, Size 228, 'Version' 19:57:17 R -> UBX NAV-PVT, Size 100, 'Navigation PVT Solution' 19:57:17 R -> UBX NAV-DOP, Size 26, 'Dilution of Precision' 19:57:18 R -> UBX NAV-PVT, Size 100, 'Navigation PVT Solution' 19:57:18 R -> UBX NAV-DOP, Size 26, 'Dilution of Precision' 19:57:18 R -> UBX NAV-PVT, Size 100, 'Navigation PVT Solution' 19:57:18 R -> UBX NAV-DOP, Size 26, 'Dilution of Precision' 19:57:18 R -> UBX NAV-PVT, Size 100, 'Navigation PVT Solution' 19:57:18 R -> UBX NAV-DOP, Size 26, 'Dilution of Precision' 19:57:18 R -> UBX MON-HW, Size 68, 'Hardware Status' 19:57:18 R -> UBX MON-HW2, Size 36, 'Extended Hardware Status' 19:57:18 R -> UBX NAV-PVT, Size 100, 'Navigation PVT Solution' 19:57:18 R -> UBX NAV-DOP, Size 26, 'Dilution of Precision' 19:57:18 R -> UBX NAV-TIMEGPS, Size 24, 'GPS System Time' 19:57:18 R -> UNKNOWN ???, Size 352, 'UNKNOWN' 19:57:18 R <- UBX MON, Size 8, 'Monitor' 19:57:27 R -> UBX NAV-PVT, Size 100, 'Navigation PVT Solution' 19:57:27 R <- UBX MON, Size 8, 'Monitor' 19:57:27 R -> UBX NAV-DOP, Size 26, 'Dilution of Precision' 19:57:27 R -> UBX MON-VER, Size 228, 'Version' 19:57:27 R -> UBX MON-VER, Size 228, 'Version' 19:57:27 R -> UBX NAV-PVT, Size 100, 'Navigation PVT Solution' 19:57:27 R -> UBX NAV-DOP, Size 26, 'Dilution of Precision' 19:57:27 R -> UBX NAV-TIMEGPS, Size 24, 'GPS System Time' 19:57:27 R -> UBX NAV-PVT, Size 100, 'Navigation PVT Solution' 19:57:27 R -> UBX NAV-DOP, Size 26, 'Dilution of Precision' 19:57:28 R -> UBX NAV-PVT, Size 100, 'Navigation PVT Solution' 19:57:28 R -> UBX NAV-DOP, Size 26, 'Dilution of Precision' 19:57:28 R -> UBX NAV-PVT, Size 100, 'Navigation PVT Solution' 19:57:28 R -> UBX NAV-DOP, Size 26, 'Dilution of Precision' 19:57:28 R -> UBX NAV-PVT, Size 100, 'Navigation PVT Solution' 19:57:28 R -> UBX NAV-DOP, Size 26, 'Dilution of Precision' (I know, there is this "MAVSerial Pass" feature in Mission planner, however, serial passthrough should also work)

Troubleshooting Steps Taken:

Parameter Configuration: I set SERIAL1_PASS = 1 and SERIAL2_PASS = 2. However, I am not receiving any data on the PC side via the Serial1 UART-to-USB adapter.

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Handling Driver Conflicts: Suspecting the GPS driver might be occupying the port, I tried setting SERIAL2_PROTOCOL = -1 (None) to release the interface, but this did not resolve the issue.
Hardware Verification: I have verified the hardware connections. When I temporarily set GPS_PORT = 1 (pretending the GPS is on Serial1), I can see the AP_Periph firmware sending outgoing GPS configuration packets (UBX polling, etc.) through the Serial1 port. This confirms the UART-to-USB adapter and the MCU’s TX/RX pins are functional.

image917×432 22.7 KB
GPS Module Verification: The GPS functionality works perfectly when I set GPS_PORT = 2 (configured as a standard GPS on Serial2). This confirms that the wiring between the MCU and the u-blox M10 is correct and functional.

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If anyone has experience with similar configurations, could you please advise on the correct settings to forward data from Serial2 to Serial1?