Polling

Definition

Polling is a method used in embedded systems to repeatedly check the status of a device or input, such as switches or sensors, at regular intervals. This technique allows a microcontroller to determine whether an event has occurred, but it can be resource-intensive since it occupies the CPU with continuous checks instead of allowing it to perform other tasks. Polling connects directly to controlling and interfacing with hardware components, timing operations, managing GPIO states, and differentiating from interrupt-driven designs.

5 Must Know Facts For Your Next Test

1. Polling is often simpler to implement than interrupts but can lead to inefficient CPU usage since it requires continuous checking instead of responding only when needed.
2. In scenarios where quick response times are critical, polling might introduce delays compared to interrupt-driven approaches.
3. Different polling strategies can be employed, such as fixed interval polling or event-driven polling, which optimizes CPU cycles based on the application requirements.
4. While polling can effectively detect changes in input devices like switches, its efficiency diminishes as the number of devices increases due to increased checking overhead.
5. Polling is commonly used in low-power applications where the system needs to remain in sleep mode most of the time and wake only to check inputs periodically.

Review Questions

• How does polling compare to interrupt-driven methods in terms of CPU resource utilization and responsiveness?
  • Polling consumes more CPU resources because it requires the processor to continuously check the status of devices instead of being interrupted by events. This can lead to responsiveness issues, especially in time-sensitive applications. In contrast, interrupt-driven methods allow the CPU to perform other tasks until an event occurs, making them generally more efficient and responsive in scenarios where timely reaction is crucial.
• Discuss how polling can affect the performance of a microcontroller when interfacing with multiple LEDs or switches.
  • When using polling with multiple LEDs or switches, the performance can be negatively impacted due to increased CPU load from checking each input at regular intervals. As the number of devices increases, the time spent polling each one can lead to significant delays in processing other tasks. This can result in slower response times for user inputs and may cause flickering in LED outputs if not managed correctly.
• Evaluate the implications of using polling for timer management in an embedded system compared to utilizing timer/counter features for event handling.
  • Using polling for timer management can introduce inefficiencies as it relies on constant checks that may miss precise timing requirements. On the other hand, utilizing timer/counter features allows for more accurate event handling since these components can generate interrupts based on specific conditions. This means that while polling may simplify design, it may not meet stringent timing constraints, leading to potential issues in applications requiring high precision and reliability.

Related terms

Interrupts: Interrupts are signals that temporarily halt the current execution of a program to address an event, allowing the CPU to respond immediately rather than polling for changes.

GPIO (General Purpose Input/Output): GPIO pins are configurable pins on a microcontroller that can be used for input or output purposes, playing a critical role in device interfacing.

Timer/Counter: Timer/counters are hardware components in microcontrollers that count events and measure time intervals, often used to generate precise timing for polling operations.