Stack
Chris;
Its both… The processor automagically uses one of the two stacks
(supervisor or user) when processing traps. There are processor
instructions that enable the user (read programmer) to also use the stack.
Just remember that if you 'mess with the stack' you must ensure that the
data and addresses that the processor is expecting for a return must be
present and in the right location/order when the return occurs.
73, bill