*procedure
**
The ENTER procedure (available on 68000s only)

ENTER is a BCPL callable function that allows arbitrary foreign code
to be run (possibly in user state) within a Tripos task.  A typical call
is the following:

                RES  :=  ENTER(REGS)

where REGS is a vector containing a complete set of machine registers
(D0-D7, A0-A6, USP, SR, and PC).  The call causes the processor to execute
instructions from that machine state.  ENTER returns if the entered code
executes any of the TRAPs 1-12, 14-15, returning the TRAP number as result
and the current state of the registers in REGS.  If the entered code faults
in any other way, the standard Tripos debugging aid is entered, thus allowing
for instance the standard breakpoint and single stepping facilities to
work.


