today we found that the reason(?) their radio drifts out of sync may be that they're using arm-linux-gnueabihf-gcc 7.2.1 and I'm using arm-linux-gnueabihf-gcc 8.3.0 <_>
luckily(??) the problem seems to be fixed for them by using -O3 (???)
i'm intending to try 7.2.1 and maybe compare the generated machine code, just need to get it to run on my Mac