Nand vs Norflash (XIP)

XIP：

The storage must provide a similar interface to the CPU as regular memory (or an adaptive layer must be present).
This interface must provide sufficiently fast read operations with a random access pattern.
The file system, if one is used, needs to expose appropriate mapping functions.
The program must either be linked to be aware of the address the storage appears at in the system or be position-independent.
The program must not modify data within the loaded image.