qmk_firmware/keyboards/phoenix/rules.mk

# MCU name
MCU = STM32F401

# Bootloader selection
BOOTLOADER = stm32-dfu

# Build Options
#   change yes to no to disable
#
BOOTMAGIC_ENABLE = lite     # Enable Bootmagic Lite
MOUSEKEY_ENABLE = yes       # Mouse keys
EXTRAKEY_ENABLE = yes       # Audio control and System control
CONSOLE_ENABLE = no         # Console for debug
COMMAND_ENABLE = no         # Commands for debug and configuration
SLEEP_LED_ENABLE = no       # Breathing sleep LED during USB suspend, do not enable SLEEP_LED_ENABLE. it uses the same timer as BACKLIGHT_ENABLE
NKRO_ENABLE = yes           # USB Nkey Rollover, if this doesn't work, see here: https://github.com/tmk/tmk_keyboard/wiki/FAQ#nkro-doesnt-work
BACKLIGHT_ENABLE = no       # Enable keyboard backlight functionality
RGBLIGHT_ENABLE = no        # Enable keyboard RGB underglow
BLUETOOTH_ENABLE = no       # Enable Bluetooth
AUDIO_ENABLE = no           # Audio output
STENO_ENABLE = no
SPLIT_KEYBOARD = yes
SERIAL_DRIVER = usart
KEYBOARD_SHARED_EP = yes

OPT_DEFS += -DSTM32_DMA_REQUIRED=TRUE