APM mission planner & Mavlink protocol

Hi all,

I'm trying to connect my STM32 based autopilot with the APM mission planner 1.2.22 Mav 1.0, with a pair of 3D Robotics 433 MHz radios, without success.

The APM recognizes the heartbeat messages sent by the autopilot but doesn't complete the connection.

After some tweaking I traced the problem back to the REQUEST PARAM LIST message sent by APM planner: contrary to the Mavlink protocol specifications, the STX character is 0x00 instead of 0xFE (for mavlink version 1.0 or 0x55 for mavilink version 0.9).

MAVLink packet

Byte IndexContentValueExplanation
       0Packet start sign    v1.0: 0xFE (v0.9: 0x55)

Indicates the start of a new packet.

All remaining fields of the message are correct: Length = 2, Sequence, System identifier = 20, Component identifier = 200, Message identifier = 22, Payload, CRC.
I checked again the specifications of Mavlink protocol, but there's no mention of a STX character = 0x00.

I thus modified the firmware of my autopilot to make it send the list of parameters without waiting for the REQUEST PARAM LIST message.
Nonetheless the APM does not recognize the parameters sent by the autopilot and times out.

By the way, with the same firmware I'm able to connect the autopilot with AqGCS running on an Android 4.0 tablet.

I kindly ask you if anyone can tell me what I'm missing.

Thank you in advance and regards

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