I've used brew install avr-gcc to setup development for older chips like the attiny85, and can use avrdude with a usbasp on my Mac / OSX.
I'd like to work with some of the newer ATTinys, but my current libc includes don't support them. I suspect I need to patch the io.h files, but can't find a tutorial on how to do that.
Also, I understand that I need a UPDI programmer. I have an ATTiny416 XplainedNano, which includes a UPDI programmer, but I think I also need a patched avrdude.conf file to use it.
I'm hoping once I can write some code to the 416 Xplained board, I can separate the UPDI programmer and use it to develop for other new ATTiny chips.
Thanks for any pointers.