The internal flash can be directly accessed by the CPU;
the external flash cannot be directly accessed by the CPU; such as the spi flash storage device, the data stored in it needs to be accessed through the spi controller.
xip: The code is local.
Non-xip: The code cannot be executed locally, and the non-xip code needs to be read into the memory through other programs before the CPU can execute the code.
The single-chip microcomputer does not have a memory management unit (mmu: mapping from virtual address to physical address), so there is no distinction between virtual address and physical address, it only has one physical address.