HP 3000 Manuals

Introduction to MPE XL for MPE V Programmers Migration Guide

Arming Traps in a Mixed Mode Programming Environment 
(new) 

One major effect of the architectural differences between MPE V/E-based
and MPE XL-based systems concerns the nature of recovery actions in the
two MPE XL programming environments, CM and NM. Results of trapping
operations on the two systems are different when you recover and
continue.  CM trap handlers cannot catch NM traps and, likewise, NM trap
handlers cannot catch CM traps.  Consequently, if your user-written code
executes in both NM and CM, then in order to catch all arithmetic,
library, and system traps, you must have both a CM and an NM trap handler
and use the Switch subsystem to arm/enable other-mode trap handlers.

The exception to the situation described above is the CONTROL-Y
(subsystem break) trap.  There is only one subsystem break handler at a
time for a process, be it CM or NM. If a CM CONTROL-Y trap handler is
armed with XCONTRAP and you hit CTRLY while the program is executing in
NM, the operating system automatically switches on your behalf to invoke
the trap handling procedure.  The converse is also true.

Refer to the Switch Programming Guide (32650-90014) for more information
about the Switch subsystem and mixed mode programming.

MPE/iX 5.0 Documentation