Added support for MCP9808 (#1026)

* Added support for MCP9808

* Fixed formatting issues

* Fixed items from comments

* Fixes from comments

* Added documentation

src/devices/Mcp9808/Mcp9808.cs

+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+using System.Device.I2c;
+using System.Threading;
+using Iot.Units;
+
+namespace Iot.Device.Mcp9808
+{
+    /// <summary>
+    /// Microchip's MCP9808 I2C Temp sensor
+    /// </summary>
+    public class Mcp9808 : IDisposable
+    {
+        private I2cDevice _i2cDevice;
+
+        /// <summary>
+        /// MCP9808 I2C Address
+        /// </summary>
+        public const byte DefaultI2cAddress = 0x18;
+
+        #region prop
+
+        /// <summary>
+        /// MCP9808 Temperature
+        /// </summary>
+        public Temperature Temperature { get => Temperature.FromCelsius(GetTemperature()); }
+
+        private bool _disable;
+
+        /// <summary>
+        /// Disable MCP9808
+        /// </summary>
+        public bool Disabled
+        {
+            get
+            {
+                return _disable;
+            }
+            set
+            {
+                SetShutdown(value);
+            }
+        }
+
+        #endregion
+
+        /// <summary>
+        /// Creates a new instance of the MCP9808
+        /// </summary>
+        /// <param name="i2cDevice">The I2C device used for communication.</param>
+        public Mcp9808(I2cDevice i2cDevice)
+        {
+            _i2cDevice = i2cDevice;
+
+            Disabled = false;
+
+            if (!Init())
+            {
+                throw new Exception("Unable to identify manufacturer/device id");
+            }
+        }
+
+        /// <summary>
+        /// Checks if the device is a MCP9808
+        /// </summary>
+        /// <returns>True if device has been correctly detected</returns>
+        private bool Init()
+        {
+            if (Read16(Register8.MCP_MANUF_ID) != 0x0054)
+            {
+                return false;
+            }
+
+            if (Read16(Register8.MCP_DEVICE_ID) != 0x0400)
+            {
+                return false;
+            }
+
+            return true;
+        }
+
+        /// <summary>
+        /// Return the internal resolution register
+        /// </summary>
+        /// <returns>Resolution setting</returns>
+        public byte GetResolution()
+        {
+            return Read8(Register8.MCP_RESOLUTION);
+        }
+
+        /// <summary>
+        /// Wakes-up the device
+        /// </summary>
+        public void Wake()
+        {
+            SetShutdown(false);
+
+            // Sleep 250 ms, which is the typical temperature conversion time for the highest resolution (page 3 in datasheet, tCONV)
+            Thread.Sleep(250);
+        }
+
+        /// <summary>
+        /// Shuts down the device
+        /// </summary>
+        public void Shutdown()
+        {
+            SetShutdown(true);
+        }
+
+        /// <summary>
+        /// Read MCP9808 Temperature (℃)
+        /// </summary>
+        /// <returns>Temperature</returns>
+        private double GetTemperature()
+        {
+            ushort value = Read16(Register8.MCP_AMBIENT_TEMP);
+
+            if (value == 0xFFFF)
+            {
+                // Return NaN if the MCP9808 doesn't have a measurement ready at the time of reading
+                return double.NaN;
+            }
+
+            double temp = value & 0x0FFF;
+            temp /= 16.0;
+            if ((value & 0x1000) != 0)
+            {
+                temp -= 256;
+            }
+
+            return Math.Round(temp, 5);
+        }
+
+        /// <summary>
+        /// Set MCP9808 Shutdown
+        /// </summary>
+        /// <param name="isShutdown">Shutdown when value is true.</param>
+        private void SetShutdown(bool isShutdown)
+        {
+            Register16 curVal = ReadRegister16(Register8.MCP_CONFIG);
+
+            if (isShutdown)
+            {
+                curVal |= Register16.MCP_CONFIG_SHUTDOWN;
+            }
+            else
+            {
+                curVal &= ~Register16.MCP_CONFIG_SHUTDOWN;
+            }
+
+            Write16(Register8.MCP_CONFIG, curVal);
+
+            _disable = isShutdown;
+        }
+
+        /// <summary>
+        /// Cleanup
+        /// </summary>
+        public void Dispose()
+        {
+            _i2cDevice?.Dispose();
+            _i2cDevice = null;
+        }
+
+        internal Register16 ReadRegister16(Register8 reg)
+        {
+            return (Register16)Read16(reg);
+        }
+
+        internal ushort Read16(Register8 reg)
+        {
+            _i2cDevice.WriteByte((byte)reg);
+            Span<byte> buf = stackalloc byte[2];
+            _i2cDevice.Read(buf);
+
+            return (ushort)(buf[0] << 8 | buf[1]);
+        }
+
+        internal void Write16(Register8 reg, Register16 value)
+        {
+            _i2cDevice.Write(new byte[]
+            {
+                (byte)reg,
+                (byte)((ushort)value >> 8),
+                (byte)((ushort)value & 0xFF)
+            });
+        }
+
+        internal byte Read8(Register8 reg)
+        {
+            _i2cDevice.WriteByte((byte)reg);
+
+            return _i2cDevice.ReadByte();
+        }
+
+        internal void Write8(Register8 reg, byte value)
+        {
+            _i2cDevice.Write(new byte[]
+            {
+                (byte)reg,
+                value
+            });
+        }
+    }
+}

src/devices/Mcp9808/Mcp9808.csproj

+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>netcoreapp2.1</TargetFramework>
+    <EnableDefaultItems>false</EnableDefaultItems>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="$(MainLibraryPath)System.Device.Gpio.csproj">
+      <AdditionalProperties>$(AdditionalProperties);RuntimeIdentifier=linux</AdditionalProperties>
+    </ProjectReference>
+    <ProjectReference Include="..\Units\Units.csproj" />
+    <Compile Include="Register.cs" />
+    <Compile Include="Mcp9808.cs" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <None Remove="README.md" />
+  </ItemGroup>
+</Project>

src/devices/Mcp9808/README.md

+# MCP9808 - Digital Temperature Sensor
+Microchip Technology Inc.’s MCP9808 digital temperature sensor converts temperatures between -20°C and +100°C to a digital word with ±0.25°C/±0.5°C (typical/maximum) accuracy
+
+## Usage
+```C#
+I2cConnectionSettings settings = new I2cConnectionSettings(1, Mcp9808.DefaultI2cAddress);
+I2cDevice device = I2cDevice.Create(settings);
+
+using(Mcp9808 sensor = new Mcp9808(device))
+{
+    double temperature = sensor.Temperature.Celsius;
+}
+```
+
+## References
+http://ww1.microchip.com/downloads/en/DeviceDoc/25095A.pdf

src/devices/Mcp9808/Register.cs

+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+namespace Iot.Device.Mcp9808
+{
+    /// <summary>
+    /// MCP9808 Register
+    /// </summary>
+    internal enum Register16 : ushort
+    {
+        MCP_CONFIG_SHUTDOWN = 0x0100,   // shutdown config
+        MCP_CONFIG_CRITLOCKED = 0x0080, // critical trip lock
+        MCP_CONFIG_WINLOCKED = 0x0040,  // alarm window lock
+        MCP_CONFIG_INTCLR = 0x0020,     // interrupt clear
+        MCP_CONFIG_ALERTSTAT = 0x0010,  // alert output status
+        MCP_CONFIG_ALERTCTRL = 0x0008,  // alert output control
+        MCP_CONFIG_ALERTSEL = 0x0004,   // alert output select
+        MCP_CONFIG_ALERTPOL = 0x0002,   // alert output polarity
+        MCP_CONFIG_ALERTMODE = 0x0001,  // alert output mode
+    }
+
+    internal enum Register8 : byte
+    {
+        MCP_CONFIG = 0x01,  // config
+        MCP_UPPER_TEMP = 0x02,  // upper alert boundary
+        MCP_LOWER_TEMP = 0x03,  // lower alert boundery
+        MCP_CRIT_TEMP = 0x04,   // critical temperature
+        MCP_AMBIENT_TEMP = 0x05,    // ambient temperature
+        MCP_MANUF_ID = 0x06,    // manufacture ID
+        MCP_DEVICE_ID = 0x07,   // device ID
+        MCP_RESOLUTION = 0x08 // resolution
+    }
+}

src/devices/Mcp9808/category.txt

+thermometer

src/devices/Mcp9808/samples/Mcp9808.Samples.csproj

+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>netcoreapp2.1</TargetFramework>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\Mcp9808.csproj" />
+    <ProjectReference Include="$(MainLibraryPath)System.Device.Gpio.csproj">
+      <AdditionalProperties>$(AdditionalProperties);RuntimeIdentifier=linux</AdditionalProperties>
+    </ProjectReference>
+    <ProjectReference Include="..\..\Units\Units.csproj" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <None Remove="README.md" />
+  </ItemGroup>
+
+</Project>

src/devices/Mcp9808/samples/Program.cs

+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+using System.Device.I2c;
+using System.Threading;
+
+namespace Iot.Device.Mcp9808.Samples
+{
+    internal class Program
+    {
+        public static void Main(string[] args)
+        {
+            I2cConnectionSettings settings = new I2cConnectionSettings(1, Mcp9808.DefaultI2cAddress);
+            I2cDevice device = I2cDevice.Create(settings);
+
+            using (Mcp9808 sensor = new Mcp9808(device))
+            {
+                while (true)
+                {
+                    // read temperature
+                    Console.WriteLine($"Temperature: {sensor.Temperature.Celsius} ℃");
+                    Console.WriteLine();
+
+                    Thread.Sleep(1000);
+                }
+            }
+        }
+    }
+}

src/devices/Mcp9808/samples/README.md

+# MCP9808 - Samples
+
+## Hardware Required
+* MCP9808
+* Male/Female Jumper Wires
+
+## Circuit
+
+* SCL - SCL
+* SDA - SDA
+* VCC - 5V
+* GND - GND
+
+## Code
+```C#
+I2cConnectionSettings settings = new I2cConnectionSettings(1, Mcp9808.DefaultI2cAddress);
+I2cDevice device = I2cDevice.Create(settings);
+
+using(Mcp9808 sensor = new Mcp9808(device))
+{
+    while (true)
+    {
+        Console.WriteLine($"Temperature: {sensor.Temperature.Celsius} ℃");
+        Console.WriteLine();
+
+        Thread.Sleep(1000);
+    }
+}
+```