X'Address is an Ada attribute where X is any object, program unit, or label, RM 13.3(10/1). [A program unit is either a package, a task unit, a protected unit, a protected entry, a generic unit, or an explicitly declared subprogram other than an enumeration literal, RM 10.1(1).]
'Address may be used to return the address of the first element allocated to X. 'Address may also be used to set the address of X for stand-alone objects and program units, RM 13.3(12).
-- A 32 bit hardware register Device_Input_Value: Interfaces.Unsigned_32;
It's not recommended to use Integer_32 in this case.