skydrop uses v7.2 of the avr-gcc toolchain. Newer toolchains tend to produce bigger binaries that won't fit on skydrops ATMEGA.

On linux you can use the provided script to set up the toolchain

cd utils/avr-toolchain
./build.sh

You can use either eclipse as build system or cmake.

mkdir build
cd build
cmake ..
make -j $(nproc)