Question

In closing, here's an interesting question. If the round-robin switch had numerous states, say a dozen or so, a single increment button might prove a little frustrating to the user. For example, if they accidentally go past the desired setting then they're forced to go all the way around again to effectively "back up". To alleviate this we could add a decrement pushbutton alongside our existing increment pushbutton. How would the code example presented above need to be altered to respond to a two button configuration? If at first this appears to be too daunting of a challenge, then break it into two parts. Initially, consider how the preceding code would need to be altered in order to change the operation of the fan speed increment button into a fan speed decrement button. That is, instead of button pushes producing the sequence offlow-med-high-off etc., implement the button to produce off-high- med-low-off etc. Once this is completed, determine how to combine this new implementation with the existing example code.

Short answer

Add a decrement logic alongside the existing increment logic and test both.

Step-by-step solution

Understand the task

The task involves modifying a round-robin switch implementation to handle two buttons: one for incrementing and one for decrementing the states. We will modify the code for decrementing and then combine it with the existing incrementing function.

Alter the code for a decrement button

Assume we have the states ordered as 'off', 'low', 'med', 'high'. The decrement button should move the state backwards, e.g., from 'high' to 'med'. Pseudocode can help clarify this: ``` if decrement_button_pressed: if current_state == 'off': current_state = 'high' elif current_state == 'high': current_state = 'med' elif current_state == 'med': current_state = 'low' elif current_state == 'low': current_state = 'off' ```

Implement the combined operation

With both increment and decrement logic, we integrate them. Here's the adjustment to the code that allows for both button inputs: ``` if increment_button_pressed: if current_state == 'off': current_state = 'low' elif current_state == 'low': current_state = 'med' elif current_state == 'med': current_state = 'high' elif current_state == 'high': current_state = 'off' if decrement_button_pressed: if current_state == 'off': current_state = 'high' elif current_state == 'high': current_state = 'med' elif current_state == 'med': current_state = 'low' elif current_state == 'low': current_state = 'off' ```

Test and validate

Test the new implementation by simulating button presses and checking if the state transitions properly. The state should move forward when the increment button is pressed and backward when the decrement button is pressed.

Key concepts

Round-Robin Scheduling

Round-robin scheduling is a simple, yet effective form of scheduling that involves cycling through tasks in a fixed order. In the context of embedded systems programming, round-robin scheduling is commonly used to manage state transitions. For example, when you have a device with multiple states like a fan with settings from 'off' to 'high', it cycles through these states, returning to the beginning after reaching the end.

In a round-robin approach:

• Each state has equal priority and time allocation.
• States are managed in a predefined sequence.
• It doesn't require a special mechanism to handle state priorities.

This scheduling is advantageous due to its simplicity and the predictability of state transitions. However, if the sequence becomes too lengthy, it may cause delay, particularly when the user navigates past their desired state. This is where implementation strategies such as adding decrement control become essential to enhance usability.

State Management

State management refers to the way in which a system handles its various modes or settings. In our fan example, the system needs to effectively track and transition between states like 'off', 'low', 'med', and 'high'.

Good state management should:

• Be efficient, ensuring quick response times between transitions.
• Clearly define how each button press will affect the current state.
• Implement checks to prevent invalid state transitions.

In implementing state management for our double-button configuration, the logic distinguishes between incrementing and decrementing states. While the increment button press moves forward, the decrement button moves backwards. This effectively addresses any issues with navigating past the desired state, offering a practical solution in user interface design.

Button Interface Design

Designing an effective button interface significantly affects usability. A well-designed button interface should be intuitive, responding accurately to user inputs without excessive delay or confusion.

For the assignment, we've considered:

• Adding a second button to decrease a setting state.
• Ensuring both buttons provide immediate feedback.
• Maintaining a logical and predictable sequence for both increment and decrement actions.

By integrating a two-button setup, users gain flexibility in navigating device settings without needing to cycle through unnecessary states. Each button offers a clear purpose: one moves settings up and the other down. The interface design must ensure that button presses are easily detected with minimal user effort, enhancing the overall user experience. This detailed attention to interface design ensures that the system is user-friendly and meets practical needs.

Choosing the right components for button detection, such as debouncing mechanisms, can prevent false detections and ensure smooth interaction.