Where is the Arduino IDE boards.txt file for Nano Every located?

Question

My Arduino Nano Every runs at 16Mhz (but the 4809 can support internal 20Mhz).
I know it may be possible to alter the boards.txt file and set it to build for 20Mhz. However, I can't find the boards.txt for these new boards (MegaAVR). Where is the boards.txt located?

Answer 1

In addition to set the

nona4809.build.f_cpu=20000000L

you will have to set the corresponding fuse byte to

nona4809.bootloader.OSCCFG=0x02

this enables the 20 MHz clock.

Answer 2

I found the boards.txt file at: ~/.arduino15/packages/arduino/hardware/megaavr/1.8.7

The Nano Every portion of the boards.txt looks like the following:

##############################################################

nona4809.name=Arduino Nano Every

nona4809.vid.0=0x2341
nona4809.pid.0=0x0058

nona4809.upload.tool=avrdude
nona4809.upload.protocol=jtag2updi
nona4809.upload.maximum_size=49152
nona4809.upload.maximum_data_size=6144
nona4809.upload.speed=115200
nona4809.upload.use_1200bps_touch=true
nona4809.upload.extra_params=-P{serial.port}

nona4809.build.mcu=atmega4809
nona4809.build.f_cpu=16000000L
nona4809.build.board=AVR_NANO_EVERY
nona4809.build.core=arduino
nona4809.build.variant=nona4809
nona4809.build.text_section_start=.text=0x0
nona4809.build.extra_flags={build.328emulation} -DMILLIS_USE_TIMERB3 -DNO_EXTERNAL_I2C_PULLUP
#nona4809.build.extra_flags=-B{runtime.tools.atpack.path}/gcc/dev/{build.mcu}

nona4809.bootloader.tool=avrdude
nona4809.bootloader.file=atmega4809_uart_bl.hex
nona4809.bootloader.SYSCFG0=0xC9
nona4809.bootloader.BOOTEND=0x00
nona4809.bootloader.OSCCFG=0x01
nona4809.fuses.file=fuses_4809.bin

menu.mode=Registers emulation
nona4809.menu.mode.on=ATMEGA328
nona4809.menu.mode.on.build.328emulation=-DAVR_NANO_4809_328MODE
nona4809.menu.mode.off=None (ATMEGA4809)
nona4809.menu.mode.off.build.328emulation=

##############################################################

If you change the following line from:

nona4809.build.f_cpu=16000000L

to:

nona4809.build.f_cpu=20000000L

Then go in and turn on verbose when you build in the Arduino IDE you will see that avrdude will pass in the following when it builds your sketch:

DF_CPU=20000000L 

Will this push the CPU to 20Mhz? Not sure, but at least you know where this is now.

UPDATE

FYI - Do not set your board to 20Mhz. Especially if you have Serial Communication going on. I have software serial set up to communicate with an attached bluetooth device and when you set the CPU to 20Mhz other things are not set properly and the Serial communication fails.