A probably naieve question. If the VPU can be used as the bootstrap loader for the CPU, much as a PDP11 on the door of the Vax 11/780 acted as bootstrap loader for the Vax, can we not simply replace all the complex VPU resident functions with 'just run on the CPU' and then resolve the external device bindings in normal CPU code?

Maybe I misread it, but it read like the VPU does more than the tiny necessary bootstrap to find an image, and chain load it. It reads like it has to do some timing critical initialisations of subsystems, but I cannot but think a CPU should be able to do this for itself, once it has some run state with a kernel in memory.

It's as if the VPU has to make the other bits of blobby hardware be alive, for the CPU to be able to see them. Most odd.

Oftentimes there are magic bits of this to do with ring states, and priviledge to alter ring at runtime. Maybe this is part of the story: the VPU initialises a specific ring state and some outer higher trust ring MUST be pre-initialised for the CPU ring state to be allowed to talk to it: it would violate the ring model, if the CPU did it.