When free-climbing don't expect there to be ropes, and that others on the mountain are focused on their own ascent, not explaining where you should put your hands and feet.
The model of how other variants for ATMEL/MICROCHIP are built should be an adequate enough template for most capable of doing the porting work.
Understand the platform and its expectations via thorough code review of things which are already working/functional, and become a chameleon..
The STM32dunio people have done it for STM32 parts, the Arduino Portenta H7 is another.
Once upon a long time ago there was the Arduino OTTO STAR
But as I understand it you'll need to make the pin level variant portions, the interrupt/table start-up code stuff, including the main code calling the setup() and loop() functionality, C++ constructor stuff, memory allocation, low level setup and interrupts, and then build of the core functionality for serial, gpio, timers, pwm, adc, dac, etc to get some semblance of functionality. And glue together all the txt and configuration files so it integrates the board nicely in the IDE.
AdaFruit has done this nicely with a lot of their ARM boards.
