Mavsdk: Cross-compile and deploy for Raspberry Pi

[julianoes]

It would actually be very nice if we could also generate a .deb for Raspbian, so it can be installed easily on Raspberry Pi.

Building on Raspberry Pi is really quite slow, especially when you would add the gRPC backend.

[JonasVautherin]

I'm not sure this is a beginner issue :sweat_smile:.

This means that you need to cross-compile all the libs for rpi, and last time I tried it was already not working for curl (I contributed to fix the bug, and I believe it was working in the end).

Still with curl, one issue we have is that we don't really compile it from sources but have this "curl-android-ios" for Android and iOS, which is already some kind of workaround.

[hamishwillee]

Love the idea.

More generally we still need an idiot proof deployment of all our runtimes for our supported platforms - ie no more pointing people to the build page at all.

[julianoes]

It's good for an SDK beginner knowing cross-compilation :smile:

More generally we still need an idiot proof deployment of all our runtimes for our supported platforms - ie no more pointing people to the build page at all.

I agree.

[julianoes]

This will be easier after #724.

[ameya7295]

I'm taking this task.

[JonasVautherin]

Wait, I can help with the latest develop! Which architecture do you need to build? armv7?

[ameya7295]

yes, I would be building for armv7, Rpi.

[JonasVautherin]

Would you mind trying with dockcross? I think I successfully built the C++ SDK (I did not try the backend):

cd /path/to/DronecodeSDK
docker run --rm dockcross/linux-armv7 > ./dockcross
chmod +x dockcross
./dockcross cmake -DCMAKE_INSTALL_PREFIX=install_armv7 -Bbuild/armv7 -S.
./dockcross cmake --build build/armv7 --target install

And then I checked that a library was indeed an ARM binary:

file install_armv7/lib/libdronecode_sdk.so
install_armv7/lib/libdronecode_sdk.so: ELF 32-bit LSB shared object, ARM, EABI5 version 1 (GNU/Linux), dynamically linked, with debug_info, not stripped

[JonasVautherin]

Seems like building the backend has issues, though ($ ./dockcross cmake -DCMAKE_INSTALL_PREFIX=install_armv7 -DBUILD_BACKEND=ON -Bbuild/armv7 -S.). @ameya7295 if you feel like debugging that, that would be awesome. It seems like FindZLIB.cmake doesn't find zlib when building gRPC. However, it also says:

CMake variable ZLIB_ROOT is set to:

/work/build/armv7/third_party/install

and zlib is indeed installed there. But still it errors with:

CMake Error at /usr/share/cmake-3.13/Modules/FindPackageHandleStandardArgs.cmake:137 (message):
  Could NOT find ZLIB (missing: ZLIB_LIBRARY ZLIB_INCLUDE_DIR)

For debugging, I would either run the dockcross image interactively (docker run --rm -it dockcross/linux-armv7 /bin/bash) or try to build on a RPi natively (i.e. without dockcross), to see if it is reproducible there.

[ameya7295]

okay, I would give this a try. thanks for sharing the required info.

[JonasVautherin]

Now wondering if it could be related to this cmake bug... :thinking:

[julianoes]

Thanks to @JonasVautherin's fix against Dockcross this should work now:

docker run --rm dockcross/linux-armv7 > ./dockcross-linux-armv7
chmod +x ./dockcross-linux-armv7
./dockcross-linux-armv7 cmake -DCMAKE_BUILD_TYPE=Release -DBUILD_BACKEND=ON -DBUILD_SHARED_LIBS=OFF -Bbuild/linux-armv7 -S.
./dockcross-linux-armv7 cmake --build build/linux-armv7 -j 8

Please re-open the issue if this is still a problem.