I see where people say one gig is 1000 mega bytes and also one gig as 1024 mega bytes.
Which one to use if we are working with microcontroller memory address space?
As you say, some people use one; other people use the other.
So just make it clear which one you are using!
I believe the standard is 1 GB = 1000 MB in favor of rounding down from 1024 over time to make things easier. As Andy says, just make clear which one you are using.