Reading through Intel's manual of the ARM64 architecture
(all 6666 pages of it!) it seems that some things are
implementation defined.

So, in the case of the RPi4 what optional features
are not included.

For example, are the four exception levels, EL3, EL2, EL1 and EL0
all implemented?

Are the encryption facilities there?

etc, etc, etc

--- SoupGate-Win32 v1.05