A few years back, I created my own custom board in the Arduino IDE, so that I could make use of the Calibrated Internal RC Oscillator in the ATMega328p. Doing that was fairly simple. I just created a new bootloader, and modified the boards.txt file so that I would have a Nano board with different fuses and a lower oscillator and clock speed.
Roll forward to 2021. I started a new project and tried to reuse my old custom board files. But there's a problem. The Arduino IDE developers decided to throw the old method of managing boards away, and create an entirely new system.
I found some guidance online, but it's for windoze, and the files don't seem to match those that are in a Linux Ubuntu installation.
So, how do I create a new board in Arduino when using Linux/Ubuntu? It should be quite simple. I just want a Nano with updated fuses and a lower oscillator/clock speed.