It's not just the direction of the stack: in theory, there are two possible kinds of downwards-growing stacks, a 'full' SP points to the last used entry, whereas an 'empty' SP points to the next free entry. It all depends upon how you 'push' something on to the stack: do you decrease the SP before or after writing the data?
ARM let you choose either approach (making four different stack configurations in total!) - this flexibility is because ARM didn't have any specialised 'push' or 'pop' operations, you read/write to the stack using the normal load/store ops, which have a variety of addressing modes.
ARM let you choose either approach (making four different stack configurations in total!) - this flexibility is because ARM didn't have any specialised 'push' or 'pop' operations, you read/write to the stack using the normal load/store ops, which have a variety of addressing modes.