Skip to content
RED SAGSkills
easyEmbedded Systems Engineer interview question

What is an interrupt, and how is it different from polling?

What the interviewer wants to hear

  • Hardware signal that pauses normal code to run an ISR
  • Polling repeatedly checks a status in a loop
  • Interrupts are efficient and responsive; polling is simple but wastes CPU
  • Interrupt priorities and nesting
  • ISRs should be short

Model answer

An interrupt is a signal, usually from hardware like a timer, GPIO pin or UART, that makes the CPU pause its current code, save its state and jump to an interrupt service routine through the vector table. When the ISR finishes, the CPU continues where it left off. Polling is the alternative: the main loop keeps checking a status flag, for example "has a byte arrived?". Polling is simple and predictable, but it wastes CPU time and power and may react late if the loop is busy. Interrupts respond quickly and let the CPU do other work or sleep until something happens. On Cortex-M, the NVIC handles priorities, so a high-priority interrupt can preempt a lower one. ISRs should be short: copy the data, set a flag or notify a task, and let the main code do the heavy processing.

Can you answer it under time pressure?

Take a timed easy round and get scored on every answer.

Start mock interview

More easy Embedded Systems Engineer questions