Using PSDK 3.3 i build the cpp application (after fixing the opencv bugs) and run it. All i get is this output:

[3.670][adapter]-[Info]-[DjiAccessAdapter_Init:145) Try identify UART0 connection failed. Probably because SDK adapter or aircraft not finish init or UART connect error.


Printed over and over. In the log file it has this:

[21.886][adapter]-[Info]-[DjiAccessAdapter_Init:145) Try identify UART0 connection failed. Probably because SDK adapter or aircraft not finish init or UART connect error.
[21.939][linker]-[Debug]-[DjiLinker_Init:124) init linker success, protocol:2, channelId:0
[21.939][linker]-[Debug]-[DjiProtocol_v1Pack:115) V1-Send: 0xE5->0x65 0x03FD
[21.959][linker]-[Debug]-[DjiProtocol_v1Pack:115) V1-Send: 0xE5->0x65 0x03FD
[21.979][linker]-[Debug]-[DjiProtocol_v1Pack:115) V1-Send: 0xE5->0x65 0x03FD
[21.999][linker]-[Debug]-[DjiProtocol_v1Pack:115) V1-Send: 0xE5->0x65 0x03FD
[22.020][linker]-[Debug]-[DjiProtocol_v1Pack:115) V1-Send: 0xE5->0x65 0x03FD
[22.045][linker]-[Debug]-[DjiLinker_DeInit:164) deinit linker success, protocol:2, channelId:0
[22.048][linker]-[Debug]-[DjiLinker_Init:124) init linker success, protocol:2, channelId:0
[22.048][linker]-[Debug]-[DjiProtocol_v1Pack:115) V1-Send: 0xE5->0x65 0x03FD
[22.068][linker]-[Debug]-[DjiProtocol_v1Pack:115) V1-Send: 0xE5->0x65 0x03FD
[22.089][linker]-[Debug]-[DjiProtocol_v1Pack:115) V1-Send: 0xE5->0x65 0x03FD
[22.109][linker]-[Debug]-[DjiProtocol_v1Pack:115) V1-Send: 0xE5->0x65 0x03FD
[22.129][linker]-[Debug]-[DjiProtocol_v1Pack:115) V1-Send: 0xE5->0x65 0x03FD
[22.154][linker]-[Debug]-[DjiLinker_DeInit:164) deinit linker success, protocol:2, channelId:0
[22.158][linker]-[Debug]-[DjiLinker_Init:124) init linker success, protocol:2, channelId:0
[22.158][linker]-[Debug]-[DjiProtocol_v1Pack:115) V1-Send: 0xE5->0x65 0x03FD
[22.172][linker]-[Debug]-[DjiProtocol_v1Unpack:192) V1-Recv: 0x65->0xE5 0x03FD
[22.178][linker]-[Debug]-[DjiProtocol_v1Pack:115) V1-Send: 0xE5->0x65 0x03FD
[22.188][linker]-[Debug]-[DjiProtocol_v1Unpack:192) V1-Recv: 0x65->0xE5 0x03FD
[22.521][utils]-[Debug]-[DjiCore_RootTask:131) work execution time:
[22.521][utils]-[Debug]-[DjiCore_RootTask:132) name

So in my case, the particular M300, the port on the top did not work, but the 2 on the bottom do ...
I tried a different M300 and it has a port on top that works.