Merge pull request #700 from arduino/karlsoderby/iotc-cheat-sheet-fix

[MKC-778] Add WDT, I2C best practices for IoTC

Author: karlsoderby

content/arduino-cloud/01.getting-started/02.technical-reference/iot-cloud-tech-ref.md

@@ -308,42 +308,89 @@ One or more **Things** can be added to a **Dashboard**, with all or some of thei
 
 ![Create widgets from a Thing](./images/create-widget-from-thing.png)
 
-***You can read more about [Dashboards & Widgets]().***
+***You can read more about [Dashboards & Widgets](/arduino-cloud/getting-started/dashboard-widgets).***
 
 ## Recommended Code Practices
 
-### Avoid blocking commands within the loop()
+This section highlights some important aspects of writing code with regard to the implementations in the [ArduinoIoTCloud](https://github.com/arduino-libraries/ArduinoIoTCloud).
+
+### Watchdog Timer (WDT)
+
+All IoT Cloud sketches use a **Watchdog Timer (WDT)** by default. The WDT can be used to automatically recover from hardware faults or unrecoverable software errors.
+
+A WDT is essentially a countdown timer, whereas it starts counting from a set value, and upon reaching zero, it resets the board. To prevent it from reaching zero, we continuously call it from the `loop()`, using the `ArduinoCloud.update()` function.
+
+This is why, it is very important to not use any long blocking code in your sketch. For example, using a long `delay()` inside the `loop()` is **strongly discouraged**, as the WDT can reach zero and reset the board.
+
+The WDT can however be disabled inside of the `setup()` function, by adding the `false` parameter:
+
+```arduino
+ArduinoCloud.begin(ArduinoIoTPreferredConnection, false).
+```
+
+***You can view the source code of this implementation [here](https://github.com/arduino-libraries/ArduinoIoTCloud/tree/master/src/utility/watchdog).***
+
+### Alternatives to Delays
 
 The `loop()` function includes the `ArduinoCloud.update();` call, which sends data to the cloud and receives updates. In order to get the best responsiveness in your cloud-connected projects, the `loop()` function should run as fast as possible. This means that no blocking commands should be used inside, and you should prefer a non-blocking programming approach whenever possible.
 
 A common **blocking pattern** is the use of the `delay()` function which stops the execution of the function for the given time. We strongly advise to **get rid of this function** and achieve the same behavior in a non-blocking way with the `millis()` function as described below.
 
 Let's see how to blink a LED. The traditional way involves the `delay()` function:
 
-    void loop() {
-      ArduinoCloud.update();
-  
-      digitalWrite(LED_BUILTIN, HIGH);
-      delay(1000);
-      digitalWrite(LED_BUILTIN, LOW);
-      delay(1000);
-    }
+```arduino
+void loop() {
+  ArduinoCloud.update();
+
+  digitalWrite(LED_BUILTIN, HIGH);
+  delay(1000);
+  digitalWrite(LED_BUILTIN, LOW);
+  delay(1000);
+}
+```
 
 This works, but it will cause a delay of at least two seconds between one execution of `ArduinoCloud.update()` and the next one, thus causing bad performance of the cloud communication.
 
 This can be rewritten in a non-blocking way as follows:
 
-    void loop() {
-      ArduinoCloud.update();
-  
-      digitalWrite(LED_PIN, (millis() % 2000) < 1000);
-    }
+```arduino
+void loop() {
+  ArduinoCloud.update();
+
+  digitalWrite(LED_PIN, (millis() % 2000) < 1000);
+}
+```
 
 How does this work? It gets the current execution time provided by `millis()` and divides it by 2 seconds. If the remainder is smaller than one second it will turn the LED on, and if it's greater it will turn the LED off.
 
 For a more complex and commented example, you can have a look at the [BlinkWithoutDelay example](/built-in-examples/digital/BlinkWithoutDelay).
 
-### Avoid waiting for Serial Monitor to initialize connection
+### I2C Usage
+
+Components connected via I²C (including the sensors onboard the [MKR IoT Carrier](https://store.arduino.cc/products/arduino-mkr-iot-carrier)) uses the same bus as the **ECCX08** cryptochip. As the crypto chip is an essential part of establishing a connection to the IoT Cloud (it contains the credentials), it is important that other I²C peripherals are initialized after the connection has been made.
+
+For example, if you are initializing a library such as [Arduino_MKRENV](https://www.arduino.cc/reference/en/libraries/arduino_mkrenv), your `setup()` should be implemented as:
+
+```arduino
+void setup() {
+  Serial.begin(9600);
+  delay(1500);
+
+  initProperties();
+
+  ArduinoCloud.begin(ArduinoIoTPreferredConnection);
+  setDebugMessageLevel(2);
+  ArduinoCloud.printDebugInfo();
+
+  //initializing the Arduino_MKRENV library
+  if (!ENV.begin()) {
+    Serial.println("Failed to initialize MKR ENV shield!");
+    while (1);
+  }
+```
+
+
+### Avoid Blocking Serial Communication
 
 `while(!Serial) {}` loops endlessly until the Serial Monitor is opened. This is a useful practice in cases where you want to see all debug output from the start of the sketch execution. However, when building IoT systems using **`while(!Serial){}` can hinder our project from running autonomously**, stopping the board from connecting to the network and IoT Cloud before manually opening the Serial Monitor. Therefore, it is recommended to consider removing the `while(!Serial){}` loop if it's not necessary.