How to go about implementing HAL crate for STM32F2

Hi!

What is the procedure for creating a HAL crate for a microcontroller. I'm in a position to be able to play around with an STM32F207-Nucleo 144 board. I'd like to try to implement a HAL implementation for STM32F2 chips, since it seems there isn't one for that family of STM32 microcontrollers yet. However, I'm not at all sure how to start or how to do it. Are there any documentation/tips?

I know about the STM32F3 HAL which is mentioned in the docs. However, I'm not too sure I understand it. Are there maybe simpler or more basic explanations of what an implementation of embedded_hal should contain, what it can add and what it should not add, etc.?

If anybody wants to contribute, I'll post a link to the repo when I create it.

VS Code's github extension found what I didn't -- an unreleased implementation of an STM32F2 HAL. I'll then contribute to that.