Enabling and disabling interrupts in Embedded C - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of enabling interrupts in embedded systems?

Enabling interrupts allows the microcontroller to respond immediately to important events by temporarily pausing the main program and running a special function called an interrupt service routine (ISR).

beginner

How do you disable interrupts in embedded C?

You disable interrupts by clearing the global interrupt enable bit, often using a function or macro like __disable_irq() or by clearing the interrupt enable flag in a control register.

intermediate

Why should interrupts sometimes be disabled temporarily?

Interrupts are disabled temporarily to protect critical sections of code from being interrupted, which prevents data corruption or inconsistent states.

intermediate

What is the difference between enabling individual interrupts and enabling global interrupts?

Enabling individual interrupts allows specific interrupt sources to trigger, while enabling global interrupts allows the CPU to respond to any enabled interrupt source.

beginner

Show a simple example in embedded C to disable and then enable interrupts.

__disable_irq(); // Disable all interrupts // Critical code here __enable_irq(); // Enable all interrupts

What happens when interrupts are disabled in an embedded system?

A The CPU ignores all interrupt requests.

B The CPU runs interrupt service routines immediately.

C The CPU resets automatically.

D The CPU speeds up execution.

Disabling interrupts means the CPU will ignore interrupt requests until they are enabled again.

Which function is commonly used in embedded C to enable global interrupts?

A interrupt_enable()

B __enable_irq()

C start_interrupts()

D enable_global()

__enable_irq() is a common intrinsic function to enable global interrupts.

Why might you disable interrupts before accessing shared data?

A To reset the microcontroller.

B To speed up the program.

C To save power.

D To prevent other code from changing the data during access.

Disabling interrupts prevents interrupt routines from modifying shared data while it is being accessed.

What is an interrupt service routine (ISR)?

A A function that resets the CPU.

B A function that disables interrupts.

C A special function that runs when an interrupt occurs.

D A function that runs only at startup.

An ISR is a special function that executes in response to an interrupt.

Which of these is NOT a reason to disable interrupts?

A Allowing the CPU to sleep.

B Preventing data corruption.

C Protecting critical code sections.

D Avoiding inconsistent program states.

Disabling interrupts is not used to put the CPU to sleep; sleep modes are handled differently.

Explain how and why interrupts are enabled and disabled in embedded C programming.

Think about how the CPU handles urgent tasks and how to safely manage shared data.

Describe a scenario where disabling interrupts is necessary and how you would implement it in code.

Consider when data might be changed by both main code and interrupts.