Alan,

“I was afraid that this was the proposal. No lower priority NS threads can run while waiting for the secure interrupt. Only higher priority threads that are initiated by a NS interrupt can run.”

You are correct, scheduling of lower priority NS threads would be not possible.  This is definitely a shortcoming of the solution.

May I ask:  how long does a hardware crypto operation take?  What time could be used for low priority NS thread execution?

Reinhard