Jameco Electronics Rabbit 3000 - Manual (Page 333)

324 Rabbit 3000 Microprocessor
C.4 Using the System/User Mode
The System/User mode is designed to work with new features in the Rabbit 3000A
(memory protection, stack protection, etc.) to provide a seamless framework for protection
of critical code. However, there are many levels at which the System/User mode can be
used; some examples are described here.
C.4.1 Memory Protection Only
At the beginning of the user program, all necessary peripherals are enabled, all peripheral
interrupts to be used are set up for the User mode, critical memory regions are protected,
stack limits are set, and the various system/memory/stack violation interrupts are enabled.
The processor then enters the User mode and remains in the User mode for all operations
(interrupts can be handled however the user desires). Obviously the critical interrupts can
be handled in the System mode, but at that point the device is typically reset and the error
is logged. An overview of this level of operation is shown in Figure C-2.
Figure C-2. System/User Mode Setup for Memory Protection Only
Critical
Interrupts
System Mode User Mode
Application
code
Interrupts
Critical
interrupts