When i truid to flash on my mac, i got 
python3 -m ufbt devboard_flash
scons: Entering directory `/Users/henry/.ufbt/current/scripts/ufbt'
scons: *** Toolchain binary arm-none-eabi-ar not found in PATH. Stop.
When i truid to flash on my mac, i got
python3 -m ufbt devboard_flash
scons: Entering directory `/Users/henry/.ufbt/current/scripts/ufbt'
scons: *** Toolchain binary arm-none-eabi-ar not found in PATH. Stop.