ARM Cortex-M3 Modes Overview

I’m preparing learning material on the operating modes of the ARM Cortex-M3 and need a clear, student-friendly walkthrough that stays at a high level. The write-up should cover all processor modes, how control flows between them, and the typical events (interrupts, exceptions, privilege changes) that trigger a switch. Alongside the text, I want a clean block diagram that visually maps each mode and the transitions in a single view. Keep the shapes and arrows straightforward—think one A4 page that can drop straight into PowerPoint or a PDF hand-out. Deliverables • Concise explanatory document (≈2-3 pages) written for learners • Editable block diagram (SVG, Visio, or PowerPoint) plus an exported PNG/PDF I’ll review for clarity, completeness of mode coverage, ARM Cortex-M3 Processor Operating Modes The ARM Cortex-M3 processor has two operating modes: Thread Mode Handler Mode 1. Thread Mode This is the normal mode in which the application program runs. After reset, the processor starts in Thread mode. It can run using either: Main Stack Pointer (MSP), or Process Stack Pointer (PSP). Thread mode can be privileged or unprivileged. 2. Handler Mode Handler mode is entered automatically when an exception or interrupt occurs. It always runs in privileged mode. It always uses the Main Stack Pointer (MSP). After the interrupt service routine (ISR) finishes, the processor returns to Thread mode. Mode Switching Diagram Plain text Reset │ ▼ +----------------------+ | Thread Mode | | (Application Code) | +----------------------+ │ Interrupt/Exception Occurs │ ▼ +----------------------+ | Handler Mode | | (ISR/Exception Code) | +----------------------+ │ Exception Return (ISR Ends) │ ▼ +----------------------+ | Thread Mode | +----------------------+ Switching Between Modes Thread Mode → Handler Mode: Occurs automatically when an interrupt or exception is generated. Handler Mode → Thread Mode: Happens automatically after the interrupt service routine executes the exception return. Key Differences Feature Thread Mode Handler Mode Purpose Executes application code Executes interrupts/exceptions Privilege Privileged or Unprivileged Always Privileged Stack Pointer MSP or PSP MSP only Entered By Reset or exception return Interrupt or exception Used For Normal program execution Interrupt Service Routines (ISRs) Exam Tip Thread Mode runs the main program, while Handler Mode runs interrupt and exception handlers. The processor automatically switches to Handler Mode during an interrupt and returns to Thread Mode when the interrupt service routine completes.

Project ID: 40565476