Arduino.Mk together with MightyCore There's no end to my frustration trying to figure out how the arduino build system works -- despite my best efforts I just can't seem to grok it. Anyhow, I did this:
ALTERNATE_CORE_PATH=/path/to/MightyCore/avr
BOARD_TAG=324
...

make show_boards shows me several boards available, including 324. Yet whenever I try to build my project, I get this error:
avr-g++: error: missing device or architecture after ‘-mmcu=’

Can someone point me in the right direction?
Thanks.
Resolved with the following Makefile options:
BOARD_TAG=324
MCU=atmega324a
VARIANT=standard