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Arduino-WDT/Arduino-WDT.ino

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+const int statePin = 3;     // Connect LattePanda's S3 pin to Arduino's D3
+const int resetPin = 4;     // Connect LattePanda's RST pin to Arduino's D4
+const int D10      = 10;
+const int D11      = 11;
+const int D12      = 12;
+ 
+bool          watchdogActive = false;
+unsigned long lastReceivedTime;
+unsigned long currentTime;
+
+bool          lastLEDState = LOW;
+unsigned long lastLEDTime;
+unsigned long currentLEDTime;
+ 
+void setup() 
+{
+  pinMode(LED_BUILTIN, OUTPUT);
+
+  digitalWrite (LED_BUILTIN, LOW);
+  lastLEDTime = millis ();
+  
+  pinMode(statePin, INPUT); // Set as input to read the state pin's level
+  pinMode(resetPin, INPUT); // By default, the RST pin on LattePanda is 3.3V. Initialize Arduino pin as INPUT to match this level.
+
+  pinMode(D10, OUTPUT);
+  pinMode(D11, OUTPUT);
+  pinMode(D12, OUTPUT);
+    
+  Serial.begin(9600);
+}
+ 
+void loop() 
+{ 
+  //-- Check to see if it's time to change the LED state.
+  currentLEDTime = millis ();
+  if (currentLEDTime > lastLEDTime) //-- Check for millis overflow
+  {
+    if (currentLEDTime - lastLEDTime > 1000U)
+    {
+      if (lastLEDState == LOW)
+      {
+        digitalWrite (LED_BUILTIN, HIGH);
+        lastLEDState = HIGH;
+      }
+      else
+      {
+        digitalWrite (LED_BUILTIN, LOW);
+        lastLEDState = LOW;  
+      }
+    
+      lastLEDTime = millis ();
+    }
+  }
+  else
+    lastLEDTime = currentLEDTime;
+     
+  // Check if the watchdog should be activated
+  if (digitalRead (statePin) == HIGH)
+  {
+    if (Serial.available () > 0) 
+    {
+      char receivedChar = Serial.read ();
+      if (receivedChar == 'A') 
+      {
+        watchdogActive = true;
+        lastReceivedTime = millis();
+      }
+      else if (receivedChar == 'Q') 
+      {
+        watchdogActive = false;
+      }
+      else if (receivedChar == '0')
+      {
+        digitalWrite (D10, LOW);
+        digitalWrite (D11, LOW);
+        digitalWrite (D12, LOW);
+      }
+      else if (receivedChar == '1')
+      {
+        digitalWrite (D10, LOW);
+        digitalWrite (D11, LOW);
+        digitalWrite (D12, LOW);
+
+        digitalWrite (D10, HIGH);
+      }
+      else if (receivedChar == '2')
+      {
+        digitalWrite (D10, LOW);
+        digitalWrite (D11, LOW);
+        digitalWrite (D12, LOW);
+
+        digitalWrite (D11, HIGH);
+      }
+      else if (receivedChar == '3')
+      {
+        digitalWrite (D10, LOW);
+        digitalWrite (D11, LOW);
+        digitalWrite (D12, LOW);
+
+        digitalWrite (D10, HIGH);
+        digitalWrite (D11, HIGH);
+      }
+      else if (receivedChar == '4')
+      {
+        digitalWrite (D10, LOW);
+        digitalWrite (D11, LOW);
+        digitalWrite (D12, LOW);
+
+        digitalWrite (D12, HIGH);
+      }
+    }
+  } 
+  else 
+  {
+    watchdogActive = false;
+  }
+
+  // If watchdog is active and 's' character isn't received within 1 minute, reboot LattePanda board
+  currentTime = millis ();
+  if (currentTime > lastReceivedTime) //-- Check for millis overflow and wait for the next cycle if it has
+  {  
+    if (watchdogActive && (currentTime - lastReceivedTime > 60000U))
+    {
+      pinMode(resetPin,OUTPUT);     // Set pin to OUTPUT mode
+      digitalWrite(resetPin, LOW);  // Pull down the RST pin to reboot the LattePanda board
+      delay(50);                    // Maintain a LOW level for 50ms
+      pinMode(resetPin, INPUT);     // Set pin back to INPUT mode to match default 3.3V level of LattePanda's RST pin
+      watchdogActive = false;       // Stop the watchdog function after rebooting the LattePanda board
+    }
+  }
+}