[qb45]

Maybe we should start with stating that the core of TZ is an execution mode of the ARM CPU privileged above the normal kernel mode, not a separate core running some obscure code. TZ can run any suitable hypervisor or just be left unused. It's nothing like the ME/PSP.

Still, some boards/devices may lock it down, for example by code signing.

[monocasa]

I think it gets obfuscated due to the fact that about the only public information that AMD provides on the PSP is that it uses ARM Trustzone technology.