Adding UART wakeup (#183)

Author: Ellerbach

README.md

@@ -106,6 +106,27 @@ S2 can only be woke up with 1 touch pad. It is recommended to do tests to find t
 Sleep.EnableWakeupByTouchPad(PadForSleep, thresholdCoefficient: 90);
 ```
 
+## UART wake up from light sleep mode
+
+It is possible to use light sleep in any supported nanoFramework ESP32 with UART wake up. There are few elements to keep in mind:
+
+* You **must** properly setup your COM port, in the following for COM2:
+
+    ```csharp
+    nanoFramework.Hardware.Esp32.Configuration.SetPinFunction(19, nanoFramework.Hardware.Esp32.DeviceFunction.COM2_TX);
+    nanoFramework.Hardware.Esp32.Configuration.SetPinFunction(21, nanoFramework.Hardware.Esp32.DeviceFunction.COM2_RX);
+    ```
+
+* Only COM1 and COM2 are supported. Note that by default COM1 is used for debug. Except if you've build your own version, you may not necessarily use it are a normal UART. But you can definitely use it to wake up your board. In that case, the pins are the default ones and the previous step is not necessary.
+* In order to wake up the board, you need to set a threshold on how many changes in the RX pin (the reception pin of the UART) is necessary. According to [the documentation](https://docs.espressif.com/projects/esp-idf/en/latest/esp32/api-reference/system/sleep_modes.html#uart-wakeup-light-sleep-only), you will lose few characters. So the sender should take this into consideration in the protocol.
+
+Usage is straight forward:
+
+```csharp
+EnableWakeupByUart(WakeUpPort.COM2, 5);
+StartLightSleep();
+```
+
 ## Pulse Counter
 
 Pulse counter allows to count pulses without having to setup a GPIO controller and events. It's a fast way to get count during a specific amount of time. This pulse counter allows as well to use 2 different pins and get a pulse count depending on their respective polarities.

nanoFramework.Hardware.Esp32/Properties/AssemblyInfo.cs

@@ -12,7 +12,7 @@
 
 ////////////////////////////////////////////////////////////////
 // update this whenever the native assembly signature changes //
-[assembly: AssemblyNativeVersion("100.0.9.0")]
+[assembly: AssemblyNativeVersion("100.0.10.0")]
 ////////////////////////////////////////////////////////////////
 
 // Setting ComVisible to false makes the types in this assembly not visible 

nanoFramework.Hardware.Esp32/Sleep.cs

@@ -175,7 +175,23 @@ public enum WakeupGpioPin : UInt64
             /// Gpio Pin 39 used for wakeup.
             /// </summary>
             Pin39 = (UInt64)1 << 39
-        }        
+        }
+
+        /// <summary>
+        /// UART port used for wakeup.
+        /// </summary>
+        public enum WakeUpPort
+        {
+            /// <summary>
+            /// COM1 port.
+            /// </summary>
+            COM1 = 0,
+
+            /// <summary>
+            /// COM2 port.
+            /// </summary>
+            COM2 = 1,
+        }
 
         /// <summary>
         /// Enable Wakeup by Timer.
@@ -228,6 +244,17 @@ public static EspNativeError EnableWakeupByTouchPad(int padNumber1, int padNumbe
             return NativeEnableWakeupByTouchPad(padNumber1, padNumber2, thresholdCoefficient);
         }
 
+        /// <summary>
+        /// Enable wakeup by UART.
+        /// </summary>
+        /// <param name="portNumber">The port to use, only COM1 and COM2 are supported. Pins MUST be properly configured for COM2 for this to work.</param>
+        /// <param name="edgeCount">The number of changes in the RX pin to wakeup the ESP.</param>
+        /// <returns>Returns ESP32 native error enumeration.</returns>
+        public static EspNativeError EnableWakeupByUart(WakeUpPort portNumber, int edgeCount)
+        {
+            return NativeEnableWakeupByUart(portNumber, edgeCount);
+        }
+
         /// <summary>
         /// Enter light sleep with the configured wakeup options. 
         /// </summary>
@@ -299,6 +326,9 @@ public static int GetWakeupTouchpad()
 
         [MethodImpl(MethodImplOptions.InternalCall)]
         private static extern EspNativeError NativeEnableWakeupByTouchPad(int padNumber1, int padNumber2, byte thresholdCoefficient);
+        
+        [MethodImpl(MethodImplOptions.InternalCall)]
+        private static extern EspNativeError NativeEnableWakeupByUart(WakeUpPort padNumber1, int edgeCount);
 
         [MethodImpl(MethodImplOptions.InternalCall)]
         private static extern EspNativeError NativeStartLightSleep();