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Observer Library Examples Details

This document provides detailed information for each example in the Observer Library. Each folder contains all source (.c) and header (.h) files. The examples are designed with safety-oriented practices, MISRA-C:2012 compliant, and use deterministic static memory. Terminal I/O is only used for demonstration and is not MISRA-compliant.

📁 Directory Layout

examples/
├─ basic_observer/        # Basic Observer Example
├─ state_observer/        # Observer with State Machine Example
├─ observer_u8/           # Observer with uint8_t Notify Argument Example
└─ ...                    # Other future examples

1️⃣ Basic Observer Example

  • Folder: examples/basic_observer/

  • Purpose: Demonstrates multiple observers reacting to a pushbutton event in a deterministic, MISRA-C compliant way.

  • Files:

File Description
main.c Entry point. Initializes modules, sets up observer subscriptions, and runs main loop.
mock_LED.c/h Mock LED observer that toggles its state on pushbutton events.
mock_LCD.c/h Mock LCD observer that prints messages to terminal on pushbutton events.
mock_pushbutton.c/h Simulates pushbutton input via terminal keyboard ('c' key) and notifies observers.

  • Detailed Description: This example demonstrates a basic observer pattern in C. The system consists of a mock pushbutton event source and two observers: a mock LED and a mock LCD display. Each press of the 'c' key triggers a notification event:

  • The pushbutton module detects the key press and calls notify() only on subscribed observers.

  • The LCD observer prints a message indicating the key press.
  • The LED observer toggles its state and prints the new state.

Static subscription tables are used to avoid dynamic memory allocation. Observer callbacks are independent. Terminal I/O uses POSIX calls for demonstration only.

  • Build & Run:
cd examples/basic_observer
cmake -S ./ -B out -G "Unix Makefiles"   # or "Ninja"
cd out
make all        # or ninja
make run        # or ninja run
  • Expected Output:
[MOCK_LCD]: Key 'C' has been pressed
[MOCK_LED]: LED IS ON
[MOCK_LCD]: Key 'C' has been pressed
[MOCK_LED]: LED IS OFF

  • Safety Notes:

  • Deterministic execution using static memory.

  • Observer callbacks are independent.

  • Terminal I/O uses POSIX calls for demonstration only, not MISRA-compliant.

  • Relation Diagrams for Initialization and Main Loop Phases:

Initialization Phase 
flowchart TD
    A[Pushbutton Module / Publisher]
    B[LED Observer]
    C[LCD Observer]

    B -->|Subscribe to pushbutton events| A
    C -->|Subscribe to pushbutton events| A

    style A fill:#444444,stroke:#ffffff,stroke-width:2px,color:#ffffff
    style B fill:#666666,stroke:#ffffff,stroke-width:1px,color:#ffffff
    style C fill:#666666,stroke:#ffffff,stroke-width:1px,color:#ffffff
Main Loop Phase 
flowchart TD
    D[update_mock_pushbutton]
    A[Pushbutton Module / Publisher]
    B[LED Observer]
    C[LCD Observer]

    D -->|Detect C key press| A
    A -->|Notify only subscribed observers| B
    A -->|Notify only subscribed observers| C

    style A fill:#444444,stroke:#ffffff,stroke-width:2px,color:#ffffff
    style B fill:#666666,stroke:#ffffff,stroke-width:1px,color:#ffffff
    style C fill:#666666,stroke:#ffffff,stroke-width:1px,color:#ffffff
    style D fill:#FFA500,stroke:#ffffff,stroke-width:1px,color:#000000

  • Explanation of Flow:

  • main.c initializes all modules (init_mock_modules()) and sets subscriptions (set_all_subscriptions()) in the Initialization Phase.

  • Main loop (for(;;)) continuously calls update_mock_pushbutton() in the Main Loop Phase.
  • When the user presses C key, pushbutton module invokes notify() only for subscribed observers.
  • LED and LCD react independently.

2️⃣ State Observer Example

  • Folder: examples/state_observer/

  • Purpose: Demonstrates observer_enter_exit API with a mock state machine alternating between ENTER and EXIT states.

  • Files:

File Description
main_state_example.c Entry point, initializes state machine and display
mock_state_machine.c/h Toggles state and notifies observers
mock_display.c/h Prints messages on state transitions

  • Detailed Description: The mock state machine toggles between ENTER and EXIT states at a fixed interval (1 second). Observers subscribed to state events are notified on every state change. The display observer prints a message indicating the current state. Deterministic notifications and static subscription tables ensure safe execution.

  • Build & Run:

cd examples/state_observer
cmake -S ./ -B out -G "Unix Makefiles"   # or "Ninja"
cd out
make all        # or ninja
make run        # or ninja run
  • Expected Output:
[DISPLAY]: State ENTER
[DISPLAY]: State EXIT
[DISPLAY]: State ENTER

  • Safety Notes:

  • Deterministic toggling between states.

  • Observers use static subscription tables.

  • Observer notifications are safe assuming external synchronization.

  • Relation Diagrams for Initialization and Main Loop Phases:

Initialization Phase 
flowchart TD
    A[State Machine / Publisher]
    B[Display Observer]

    B -->|Subscribe to state events| A

    style A fill:#444444,stroke:#ffffff,stroke-width:2px,color:#ffffff
    style B fill:#666666,stroke:#ffffff,stroke-width:1px,color:#ffffff
Main Loop Phase 
flowchart TD
    D[update_mock_state_machine]
    A[State Machine / Publisher]
    B[Display Observer]

    D -->|Toggle state| A
    A -->|Notify subscribed observers| B

    style A fill:#444444,stroke:#ffffff,stroke-width:2px,color:#ffffff
    style B fill:#666666,stroke:#ffffff,stroke-width:1px,color:#ffffff
    style D fill:#FFA500,stroke:#ffffff,stroke-width:1px,color:#000000

3️⃣ Observer with uint8_t Notify Argument Example

  • Folder: examples/observer_u8/

  • Purpose: Demonstrates observer_u8 API with periodic mock sensor updates.

  • Files:

File Description
main_sensor_example.c Entry point, initializes sensor and logger
mock_sensor.c/h Generates periodic sensor values and notifies observers
mock_logger.c/h Logs sensor value to stdout

  • Detailed Description: The mock sensor generates incrementing uint8_t values at a fixed interval (0.5 seconds). Each new sensor value is sent to all subscribed observers using the observer_u8 API. The logger observer prints the sensor value to the terminal. Deterministic updates, static memory, and safe observer execution are ensured when subscription tables are properly sized.

  • Build & Run:

cd examples/observer_u8
cmake -S ./ -B out -G "Unix Makefiles"   # or "Ninja"
cd out
make all        # or ninja
make run        # or ninja run
  • Expected Output:
[LOGGER]: Sensor value = 1
[LOGGER]: Sensor value = 2
[LOGGER]: Sensor value = 3

  • Safety Notes:

  • Static memory only.

  • Deterministic updates.

  • Observer callbacks independent.

  • Relation Diagrams for Initialization and Main Loop Phases:

Initialization Phase 
flowchart TD
    A[Mock Sensor / Publisher]
    B[Logger Observer]

    B -->|Subscribe to sensor updates| A

    style A fill:#444444,stroke:#ffffff,stroke-width:2px,color:#ffffff
    style B fill:#666666,stroke:#ffffff,stroke-width:1px,color:#ffffff
Main Loop Phase 
flowchart TD
    D[update_mock_sensor]
    A[Mock Sensor / Publisher]
    B[Logger Observer]

    D -->|Increment sensor value| A
    A -->|Notify subscribed observers| B

    style A fill:#444444,stroke:#ffffff,stroke-width:2px,color:#ffffff
    style B fill:#666666,stroke:#ffffff,stroke-width:1px,color:#ffffff
    style D fill:#FFA500,stroke:#ffffff,stroke-width:1px,color:#000000


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