Polling or Interrupt based method

Question

When should one use polling method and when should one use interrupt based method ? Are there scenarios in which both can be used ?

Answer 1

There are many design constraints that can drive the decision. My app has a combination of interrupt and polling:

• External and internal clock sources trigger interrupts - it's critical to timestamp both accurately so we can synchronize them.
• Incoming serial messages trigger interrupts. The recieve FIFOs must be serviced before they overflow.
• Outgoing messages trigger interrupts when the FIFO is partially empty - it must be refilled before it underflows.
• The ISR's set semaphores that are polled for in the background. This has 2 advantages:
  • The computation needed to handle incoming events can be lengthy; if it were left in the ISR it could delay other ISRs beyond their service deadlines.
  • Events can be sequenced. For instance, a polling loop can ensure that calculation X always occurs between ADC data collection and incoming message parsing, even if sometimes the message arrives a little earlier than expected.