Summary

This follow-up article continues the deep dive into Cortex-M exception mechanics, focusing on stacking/unstacking, entry/exit timing, tail-chaining, and priority masking. It also covers how these behaviors interact with RTOS context switching (PendSV/SVC), lazy FPU stacking, and practical fault-diagnosis techniques the reader can apply to real firmware.

Key Takeaways

• Explain how Cortex-M stacks and unstacks registers on exception entry/exit and how to interpret the stacked frame for debugging.
• Describe tail-chaining and lazy FPU stacking and quantify their impact on interrupt latency.
• Use PRIMASK, BASEPRI, FAULTMASK, and NVIC priority grouping correctly to control preemption and protect critical sections.
• Design RTOS-friendly context switches using PendSV/SVC and avoid common pitfalls with nested interrupts and priority inversion.
• Apply practical methods to diagnose HardFault/BusFault/UsageFault causes by analyzing stack frames and SCB registers.

Who Should Read This

Embedded firmware engineers working with Cortex-M microcontrollers or RTOS-based systems who need a deeper, practical understanding of exception behavior, interrupt latency, and fault debugging.

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