ARM R4F, r1p3 manual Coprocessor instructions, Effect of debug state on non-invasive debug

Debug

11.8.7Coprocessor instructions

CP14 and CP15 instructions can always be executed in debug state regardless of processor mode.

11.8.8Effect of debug state on non-invasive debug

The processor non-invasive debug features are the ETM and Performance Monitoring Unit (PMU). All of these non-invasive debug features are disabled when the processor is in debug state. For more information, see Chapter 4 System Control Coprocessor and ETM interface on page 1-11.

When the processor is in debug state:

•the ETM ignores all instructions and data transfers

•PMU events are not counted

•events are not visible to the ETM

•the PMU Cycle Count Register (CCNT) is stopped.

11.8.9Effects of debug events on processor registers

On entry to debug state, the processor does not update any general-purpose or program status register. This includes the SPSR_abt and R14_abt registers. In addition, the processor does not update any coprocessor registers, including the CP15 IFSR, DFSR, DFAR, or IFAR registers, except for CP14 DSCR[5:2] method-of-entry bits. These bits indicate the type of debug event that caused the entry into debug state.

Note

On entry to debug state, the processor updates the WFAR register with the address of the instruction accessing the watchpointed address plus:

•+ 8 in ARM state

•+ 4 in Thumb state.

11.8.10Exceptions in debug state

While in debug state, exceptions are handled as follows:

Reset	This exception is taken as in a normal processor state. This means the processor
	leaves debug state because of the system reset.

Prefetch Abort

This exception cannot occur because the processor does not fetch any instructions while in debug state.

Debug The processor ignores debug events, including BKPT instructions.

SVC The processor ignores SVC exceptions.

Undefined

When an Undefined exception occurs in debug state, the behavior of the processor is as follows:

•PC, CPSR, SPSR_und, and R14_und are unchanged

•the processor remains in debug state

•DSCR[8], sticky Undefined bit, is set.

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