16.10.2.3 Operation From the CPU

Only secure hosts can access the DSU internal address space. Attempting to access the internal address space from a non-secure AHB host will report a PAC error, such accesses are discarded. The external address space can be accessed by either secure or non-secure AHB hosts. The user should access DSU registers in the internal address range (0x0 – 0xFF) to avoid external security restrictions. Refer to 16.8 Security Enforcement.