User guide

Programmers Model

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3.2 Modes of operation and execution

This section briefly describes the modes of operation and execution of the Cortex-M3 processor.

See the ARMv7-M Architecture Reference Manual for more information.

3.2.1 Operating modes

The processor supports two modes of operation, Thread mode and Handler mode:

• The processor enters Thread mode on Reset, or as a result of an exception return.

Privileged and Unprivileged code can run in Thread mode.

• The processor enters Handler mode as a result of an exception. All code is privileged in

Handler mode.

3.2.2 Operating states

The processor can operate in one of two operating states:

• Thumb state. This is normal execution running 16-bit and 32-bit halfword aligned Thumb

instructions.

• Debug State. This is the state when the processor is in halting debug.

3.2.3 Privileged access and user access

Code can execute as privileged or unprivileged. Unprivileged execution limits or excludes

access to some resources. Privileged execution has access to all resources. Handler mode is

always privileged. Thread mode can be privileged or unprivileged.