An interpreter invocation mechanism for switching between execution of native
instruction words to interpreted instruction words uses a subroutine call instruction
to start execution of the interpreter. The return address of the subroutine call
instruction is used as an address pointer to the start of the interpreted code.
The interpreted code may terminate with an Exit instruction whereupon normal native
code execution resumes using the instruction at the immediately following memory
address or alternatively with a Return instruction that recovers a return address
previously stored to stack memory.
