12.2.2. Monitor debug-mode debugging

When the processor debug unit is in Monitor debug-mode, the processor takes a debug exception instead of halting. A special piece of software, a monitor target, can then take control to examine or alter the processor state. Monitor debug-mode is essential in real-time systems where the processor cannot be halted to collect information. Examples of these systems are engine controllers and servo mechanisms in hard drive controllers that cannot stop the code without physically damaging the components.

When debugging in Monitor debug-mode, the processor stops execution of the current program and starts execution of a monitor target. The state of the processor is preserved in the same manner as all ARM exceptions. The monitor target communicates with the debugger to access processor and coprocessor state, and to access memory contents and peripherals. Monitor debug-mode requires a debug monitor program to interface between the debug hardware and the software debugger.

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