Nested interrupts in Embedded C - Cheat Sheet & Quick Revision

Recall & Review

beginner

What are nested interrupts in embedded systems?

Nested interrupts allow an interrupt to be interrupted by another higher-priority interrupt before the first one finishes. This helps handle urgent tasks quickly.

intermediate

How does the processor handle nested interrupts?

The processor saves the current interrupt context, enables interrupts again, and then handles the new higher-priority interrupt. After finishing, it returns to the previous interrupt.

beginner

Why is it important to manage interrupt priorities in nested interrupts?

Managing priorities ensures that the most critical tasks interrupt less critical ones, preventing delays in urgent processing and avoiding conflicts.

intermediate

What can happen if nested interrupts are not handled properly?

Improper handling can cause stack overflow, data corruption, or system crashes because the processor may lose track of interrupt contexts.

intermediate

How can you enable nested interrupts in C for an embedded system?

You typically enable nested interrupts by setting interrupt priority levels and re-enabling global interrupts inside an interrupt service routine (ISR). For example, calling __enable_irq() inside an ISR in ARM Cortex-M.

What does nested interrupts allow in an embedded system?

A Only one interrupt can occur at a time

B Interrupts are disabled permanently

C Interrupts are ignored

D An interrupt can be interrupted by a higher-priority interrupt

Nested interrupts allow a higher-priority interrupt to interrupt a currently running interrupt.

What must be saved to handle nested interrupts correctly?

A Only global variables

B Current interrupt context (registers and state)

C Nothing needs to be saved

D Only the program counter

The processor saves the current interrupt context to resume correctly after handling nested interrupts.

Which of these is a risk if nested interrupts are not managed properly?

A Stack overflow

B Faster execution

C More memory available

D No effect

Improper nested interrupt handling can cause stack overflow due to too many saved contexts.

How do you typically enable nested interrupts inside an ISR?

A Re-enable global interrupts inside the ISR

B Disable all interrupts permanently

C Ignore interrupt priorities

D Use a delay function

Re-enabling global interrupts inside an ISR allows higher-priority interrupts to occur.

Why are interrupt priorities important in nested interrupts?

A They slow down the system

B They disable interrupts

C They decide which interrupt can interrupt another

D They are not important

Priorities determine which interrupts can preempt others in nested interrupt handling.

Explain how nested interrupts work and why they are useful in embedded systems.

Think about how urgent tasks can interrupt less urgent ones.

Describe the risks of not handling nested interrupts properly and how to avoid them.

Consider what happens if the system loses track of interrupt states.