Multiple Drone CAN mavlink 2 serial ports on the same AP_Periph device failing

[lthall]

Bug report

When connecting multiple CAN serial ports through the same AP_Periph device everything seems to work initially. After a short period of time one or both serial ports stops working.

Setup:
Three Mission planners running each set to differnt GCS ID's

1. Connected to USB on the autopilot (Durandal and 500000 baud for me)
2. Connected to AP_Periph node, serial port 1, 115200 baud (any combination also has problem)
3. Connected to AP_Periph node, serial port 2, 115200 baud (any combination also has problem)

Saleae set up to monitor the TX of the two AP_Periph nodes.

ArduCopter V4.7.0-dev (73d8f1b)

AP_Periph compiled from master too.

To repeat:
Power up and connect to USB with Mission Planner 1
Connect to AP_Periph Serial Port 1 with Mission Planner 2 (all works)
Connect to AP_Periph Serial Port 2 with Mission Planner 3 (starts to work)
Mission Planner 2 or 3 stops working, sometimes both, generally very quickly.
No TX data seen on the Saleae.
Heartbeat from GCS nodes from two AP_Periph connected Mission Planners show up when using the Mavlink Inspector on the USB connected Mission Planner.

After dissoconnecting mission planners connected to the AP_Periph. Reseting the AP_Periph starts the TX on both serial ports again.
After connecting an AP_Periph Mission Planner again it all stops.
Attempts to connect the second Mission Planner fails but both show up as heatbeats on the Mavlink Inspector.

With no connections to the AP_Periph active (both Mission Planners dissconnected) and no TX seen on the Saleae there are still UAVCAN Inspector messages being sent to both ports:

FSO_AP_Periph used:
https://github.com/lthall/Leonard_ardupilot/tree/20250325_FSO_AP_Periph

Same branch used to compile Master for Durandal.

[olliw42]

maybe or maybe not related, there appear to be other issues with mavlink via dronecan too: #28545. just to have mentioned it, in case a connection should exist.