Jameco Electronics 2000, 3000 manual C.4 Using the System/User Mode, C.4.1 Memory Protection Only

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C.4 Using the System/User Mode

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.

System Mode

 

User Mode

Critical

 

Application

 

code

interrupts

 

 

 

Critical

Interrupts

 

Interrupts

 

 

Figure C-2. System/User Mode Setup for Memory Protection Only

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Rabbit 3000 Microprocessor

Page 333
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Jameco Electronics 2000, 3000 manual C.4 Using the System/User Mode, C.4.1 Memory Protection Only