feat(gpio): new functional interrupt lambda example

Author: SuGlider

libraries/ESP32/examples/GPIO/FunctionalInterruptLambda/FunctionalInterruptLambda.ino

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+/*
+   SPDX-FileCopyrightText: 2025 Espressif Systems (Shanghai) CO LTD
+
+   SPDX-License-Identifier: Apache-2.0
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+
+   ESP32 Lambda FunctionalInterrupt Example
+   ========================================
+   
+   This example demonstrates how to use lambda functions with FunctionalInterrupt
+   for GPIO pin interrupt callbacks on ESP32. It shows different lambda patterns
+   and capture techniques for interrupt handling with debouncing.
+
+   Hardware Setup:
+   - Connect a button between GPIO 4 (BUTTON_PIN) and GND (with internal pullup)
+   - Connect an LED with resistor to GPIO 2 (LED_PIN or use the built-in LED available on most boards)
+   - Optionally connect a second button (BUTTON2_PIN) to another pin in case that there is no BOOT pin button available
+
+   Features Demonstrated:
+   1. CHANGE mode lambda to handle both RISING and FALLING edges on same pin
+   2. Lambda function with captured variables (pointers)
+   3. Object method calls integrated within lambda functions
+   4. Edge type detection using digitalRead() within ISR
+   5. Hardware debouncing with configurable timeout
+   6. Best practices for interrupt-safe lambda functions
+
+   IMPORTANT NOTE ABOUT ESP32 INTERRUPT BEHAVIOR:
+   - Only ONE interrupt handler can be attached per GPIO pin at a time
+   - Calling attachInterrupt() on a pin that already has an interrupt will override the previous one
+   - This applies regardless of edge type (RISING, FALLING, CHANGE)
+   - If you need both RISING and FALLING detection on the same pin, use CHANGE mode
+     and determine the edge type within your handler by reading the pin state
+
+   For detailed documentation, patterns, and best practices, see README.md
+
+   Note: This example uses proper pointer captures for static/global variables
+         to avoid compiler warnings about non-automatic storage duration.
+*/
+
+#include <Arduino.h>
+#include <FunctionalInterrupt.h>
+
+// Pin definitions
+#define BUTTON_PIN      4        // Button pin (GPIO 4) - change as needed
+#define BUTTON2_PIN     BOOT_PIN // BOOT BUTTON - change as needed
+#ifdef LED_BUILTIN
+#define LED_PIN         LED_BUILTIN
+#else
+#warning Using LED_PIN = GPIO 2 as default - change as needed
+#define LED_PIN         2        // change as needed
+#endif
+
+
+// Global variables for interrupt counters (volatile for ISR safety)
+volatile uint32_t buttonPressCount = 0;
+volatile uint32_t buttonReleaseCount = 0;  // Track button releases separately
+volatile uint32_t button2PressCount = 0;
+volatile bool buttonPressed = false;
+volatile bool buttonReleased = false;     // Flag for button release events
+volatile bool button2Pressed = false;
+volatile bool ledState = false;
+volatile bool ledStateChanged = false;    // Flag to indicate LED needs updating
+
+// Variables to demonstrate lambda captures
+uint32_t totalInterrupts = 0;
+unsigned long lastInterruptTime = 0;
+
+// Debouncing variables (volatile for ISR safety)
+volatile unsigned long lastButton1InterruptTime = 0;
+volatile unsigned long lastButton2InterruptTime = 0;
+const unsigned long DEBOUNCE_DELAY_MS = 50;  // 50ms debounce delay
+
+// State-based debouncing to prevent hysteresis issues
+volatile bool lastButton1State = HIGH;  // Track last stable state (HIGH = released)
+volatile bool lastButton2State = HIGH;  // Track last stable state (HIGH = released)
+
+// Class example for demonstrating lambda with object methods
+class InterruptHandler {
+  public:
+    volatile uint32_t objectPressCount = 0;
+    volatile bool stateChanged = false;
+    String name;
+
+    InterruptHandler(const String& handlerName) : name(handlerName) {}
+
+    void handleButtonPress() {
+      uint32_t temp = objectPressCount;
+      temp++;
+      objectPressCount = temp;
+      stateChanged = true;
+    }
+
+    void printStatus() {
+      if (stateChanged) {
+        Serial.printf("Handler '%s': Press count = %lu\r\n", name.c_str(), objectPressCount);
+        stateChanged = false;
+      }
+    }
+};
+
+// Global handler instance for object method example
+static InterruptHandler globalHandler("ButtonHandler");
+
+void setup() {
+  Serial.begin(115200);
+  delay(1000); // Allow serial monitor to connect
+
+  Serial.println("ESP32 Lambda FunctionalInterrupt Example");
+  Serial.println("========================================");
+
+  // Configure pins
+  pinMode(BUTTON_PIN, INPUT_PULLUP);
+  pinMode(BUTTON2_PIN, INPUT_PULLUP);
+  pinMode(LED_PIN, OUTPUT);
+  digitalWrite(LED_PIN, LOW);
+
+  // Example 1: CHANGE mode lambda to handle both RISING and FALLING edges
+  // This demonstrates how to properly handle both edges on the same pin
+  // Includes: object method calls, pointer captures, and state-based debouncing
+  Serial.println("Setting up Example 1: CHANGE mode lambda for both edges");
+
+  // Create pointers for safe capture (avoiding non-automatic storage duration warnings)
+  InterruptHandler* handlerPtr = &globalHandler;
+  volatile unsigned long* lastButton1TimePtr = &lastButton1InterruptTime;
+  volatile bool* lastButton1StatePtr = &lastButton1State;
+  const unsigned long* debounceDelayPtr = &DEBOUNCE_DELAY_MS;
+
+  std::function<void()> changeModeLambda = [handlerPtr, lastButton1TimePtr, lastButton1StatePtr, debounceDelayPtr]() {
+    // Debouncing: check if enough time has passed since last interrupt
+    unsigned long currentTime = millis();
+    if (currentTime - (*lastButton1TimePtr) < (*debounceDelayPtr)) {
+      return; // Ignore this interrupt due to bouncing
+    }
+
+    // Read current pin state to determine edge type
+    bool currentState = digitalRead(BUTTON_PIN);
+
+    // State-based debouncing: only process if state actually changed
+    if (currentState == (*lastButton1StatePtr)) {
+      return; // No real state change, ignore (hysteresis/noise)
+    }
+
+    // Update timing and state
+    (*lastButton1TimePtr) = currentTime;
+    (*lastButton1StatePtr) = currentState;
+
+    if (currentState == LOW) {
+      // FALLING edge detected (button pressed)
+      uint32_t temp = buttonPressCount;
+      temp++;
+      buttonPressCount = temp;
+      buttonPressed = true;
+
+      // Call object method for press events
+      handlerPtr->handleButtonPress();
+    } else {
+      // RISING edge detected (button released)
+      uint32_t temp = buttonReleaseCount;
+      temp++;
+      buttonReleaseCount = temp;
+      buttonReleased = true;
+
+      // Object method calls can be different for release events
+      // For demonstration, we'll call the same method but could be different
+      handlerPtr->handleButtonPress();
+    }
+  };
+  attachInterrupt(BUTTON_PIN, changeModeLambda, CHANGE);
+
+  // Example 2: Lambda with captured variables (Pointer Captures)
+  // This demonstrates safe capture of global variables via pointers
+  // NOTE: We avoid calling digitalWrite() directly in ISR to prevent FreeRTOS scheduler issues
+  Serial.println("Setting up Example 2: Lambda with pointer captures");
+
+  // Create pointers to avoid capturing static/global variables directly
+  uint32_t* totalInterruptsPtr = &totalInterrupts;
+  unsigned long* lastInterruptTimePtr = &lastInterruptTime;
+  volatile bool* ledStatePtr = &ledState;
+  volatile bool* ledStateChangedPtr = &ledStateChanged;
+  volatile unsigned long* lastButton2TimePtr = &lastButton2InterruptTime;
+  volatile bool* lastButton2StatePtr = &lastButton2State;
+
+  std::function<void()> captureLambda = [totalInterruptsPtr, lastInterruptTimePtr, ledStatePtr, ledStateChangedPtr, lastButton2TimePtr, lastButton2StatePtr, debounceDelayPtr]() {
+    // Debouncing: check if enough time has passed since last interrupt
+    unsigned long currentTime = millis();
+    if (currentTime - (*lastButton2TimePtr) < (*debounceDelayPtr)) {
+      return; // Ignore this interrupt due to bouncing
+    }
+
+    // Read current pin state and check for real state change
+    bool currentState = digitalRead(BUTTON2_PIN);
+
+    // State-based debouncing: only process if state actually changed to LOW (pressed)
+    // and the last state was HIGH (released)
+    if (currentState != LOW || (*lastButton2StatePtr) != HIGH) {
+      return; // Not a valid press event, ignore
+    }
+
+    // Update timing and state
+    (*lastButton2TimePtr) = currentTime;
+    (*lastButton2StatePtr) = currentState;
+
+    // Update button press count
+    uint32_t temp = button2PressCount;
+    temp++;
+    button2PressCount = temp;
+    button2Pressed = true;
+
+    // Update captured variables via pointers
+    (*totalInterruptsPtr)++;
+    (*lastInterruptTimePtr) = millis();
+
+    // Toggle LED state and set flag for main loop to handle
+    (*ledStatePtr) = !(*ledStatePtr);
+    (*ledStateChangedPtr) = true;  // Signal main loop to update LED
+  };
+  attachInterrupt(BUTTON2_PIN, captureLambda, FALLING);
+
+  Serial.println();
+  Serial.println("Lambda interrupts configured:");
+  Serial.printf("- Button 1 (Pin %d): CHANGE mode lambda (handles both press and release)\r\n", BUTTON_PIN);
+  Serial.printf("- Button 2 (Pin %d): FALLING mode lambda with LED control\r\n", BUTTON2_PIN);
+  Serial.printf("- Debounce delay: %lu ms for both buttons\r\n", DEBOUNCE_DELAY_MS);
+  Serial.println();
+  Serial.println("Press and release the buttons to see lambda interrupts in action!");
+  Serial.println("Button 1 will detect both press (FALLING) and release (RISING) events.");
+  Serial.println("Button 2 (FALLING only) will toggle the LED.");
+  Serial.println("Both buttons include debouncing to prevent mechanical bounce issues.");
+  Serial.println();
+}
+
+void loop() {
+  static unsigned long lastPrintTime = 0;
+  static uint32_t lastButton1PressCount = 0;
+  static uint32_t lastButton1ReleaseCount = 0;
+  static uint32_t lastButton2Count = 0;
+
+  // Handle LED state changes (ISR-safe approach)
+  if (ledStateChanged) {
+    ledStateChanged = false;
+    digitalWrite(LED_PIN, ledState);
+  }
+
+  // Update button states in main loop (for proper state tracking)
+  // This helps prevent hysteresis issues by updating state when buttons are actually released
+  static bool lastButton2Reading = HIGH;
+  bool currentButton2Reading = digitalRead(BUTTON2_PIN);
+  if (currentButton2Reading == HIGH && lastButton2Reading == LOW) {
+    // Button 2 was released, update state
+    lastButton2State = HIGH;
+  }
+  lastButton2Reading = currentButton2Reading;
+
+  // Check for button 1 presses and releases (CHANGE mode lambda)
+  if (buttonPressed) {
+    buttonPressed = false;
+    Serial.printf("==> Button 1 PRESSED! Count: %lu (FALLING edge detected)\r\n", buttonPressCount);
+  }
+
+  if (buttonReleased) {
+    buttonReleased = false;
+    Serial.printf("==> Button 1 RELEASED! Count: %lu (RISING edge detected)\r\n", buttonReleaseCount);
+  }
+
+  // Check for button 2 presses (capture lambda)
+  if (button2Pressed) {
+    button2Pressed = false;
+    Serial.printf("==> Button 2 pressed! Count: %lu, LED: %s (Capture lambda)\r\n",
+                  button2PressCount, ledState ? "ON" : "OFF");
+  }
+
+  // Check object handler status (object method lambda)
+  globalHandler.printStatus();
+
+  // Print statistics every 5 seconds if there's been activity
+  if (millis() - lastPrintTime >= 5000) {
+    lastPrintTime = millis();
+
+    bool hasActivity = (buttonPressCount != lastButton1PressCount ||
+                        buttonReleaseCount != lastButton1ReleaseCount ||
+                        button2PressCount != lastButton2Count);
+
+    if (hasActivity) {
+      Serial.println("============================");
+      Serial.println("Lambda Interrupt Statistics:");
+      Serial.println("============================");
+      Serial.printf("Button 1 presses:     %8lu\r\n", buttonPressCount);
+      Serial.printf("Button 1 releases:    %8lu\r\n", buttonReleaseCount);
+      Serial.printf("Button 2 presses:     %8lu\r\n", button2PressCount);
+      Serial.printf("Object handler calls: %8lu\r\n", globalHandler.objectPressCount);
+      Serial.printf("Total interrupts:     %8lu\r\n", totalInterrupts);
+      Serial.printf("LED state:            %8s\r\n", ledState ? "ON" : "OFF");
+      if (lastInterruptTime > 0) {
+        Serial.printf("Last interrupt:       %8lu ms ago\r\n", millis() - lastInterruptTime);
+      }
+      Serial.println();
+
+      lastButton1PressCount = buttonPressCount;
+      lastButton1ReleaseCount = buttonReleaseCount;
+      lastButton2Count = button2PressCount;
+    }
+  }
+
+  // Small delay to prevent overwhelming the serial output
+  delay(10);
+}