4.3.9.1 Memx Address Space Qualifier

Using both the __memx and const qualifiers indicates that the object is to be placed in the program space. This method of placing objects in flash is now largely redundant, as you can perform the same task using just the const qualifier, see Const Type Qualifier. The __memx qualifier is not needed when compiling for any device that maps the program memory into their data memory space, such as the avrxmega3 and tinyAVR devices.

Pointers that use this qualifier can reference both data and program memory spaces in a similar way to pointers to const, see Pointers to Both Memory Spaces.