How is UEFI binded to hardware


I'm looking to write a program to send data through an I2C protocol on my board.
How is UEFI binded to the pins on the board so that when I write and read from a pin I'm sure that the board is behaving as I'm expecting?
I understand that UEFI is purposefully abstract, but I cannot find how edkii makes that connection to the board.
Any and all information is appreciated.