In case you have a trouble for updating the tap, perform uninstalling of the related tools and osx-cross/avr
tap:
brew remove avr-binutils avr-gcc
brew untap osx-cross/avr
For installing the tap, do the following:
brew tap osx-cross/avr
brew install avr-gcc
# avrdude is under homebrew-core
brew install avrdude
Remember the 1k BIGBOOT code image must be booted from byte address 0x7c00 in GNU or 0x3c00 in ATmega328p.
The hfuse value must be 0xDC if EESAVE is not enabled (=set to 0), 0xD4 if EESAVE is enabled.