add ability to manually sync with NTP

Source/Meadow.Contracts/Hardware/INtpClient.cs

@@ -1,31 +1,38 @@
 using System;
+using System.Threading.Tasks;
 
-namespace Meadow
+namespace Meadow;
+
+/// <summary>
+/// Delegate representing a time changed event handler.
+/// </summary>
+/// <param name="utcTime">The updated UTC time.</param>
+public delegate void TimeChangedEventHandler(DateTime utcTime);
+
+/// <summary>
+/// Interface for a Network Time Protocol (NTP) client object.
+/// </summary>
+public interface INtpClient
 {
     /// <summary>
-    /// Delegate representing a time changed event handler.
+    /// Event called when the time is changed.
     /// </summary>
-    /// <param name="utcTime">The updated UTC time.</param>
-    public delegate void TimeChangedEventHandler(DateTime utcTime);
+    event TimeChangedEventHandler TimeChanged;
 
     /// <summary>
-    /// Interface for a Network Time Protocol (NTP) client object.
+    /// Gets a value indicating whether the NTP client is enabled.
     /// </summary>
-    public interface INtpClient
-    {
-        /// <summary>
-        /// Event called when the time is changed.
-        /// </summary>
-        event TimeChangedEventHandler TimeChanged;
+    bool Enabled { get; }
 
-        /// <summary>
-        /// Gets a value indicating whether the NTP client is enabled.
-        /// </summary>
-        bool Enabled { get; }
+    /// <summary>
+    /// Gets or sets the poll period for NTP synchronization.
+    /// </summary>
+    TimeSpan PollPeriod { get; set; }
 
-        /// <summary>
-        /// Gets or sets the poll period for NTP synchronization.
-        /// </summary>
-        TimeSpan PollPeriod { get; set; }
-    }
+    /// <summary>
+    /// Start an NTP time synchronization
+    /// </summary>
+    /// <param name="ntpServer">An optional NTP server address.  If null, the device will use the platform-configured NTP server address</param>
+    /// <returns><b>true</b> if successful, otherwise <b>false</b></returns>
+    Task<bool> Synchronize(string? ntpServer = null);
 }

Source/Meadow.Contracts/ISleepAwarePeripheral.cs

@@ -12,13 +12,11 @@ public interface ISleepAwarePeripheral
     /// Called before the platform goes into Sleep state
     /// </summary>
     /// <param name="cancellationToken"></param>
-    /// <returns></returns>
     public Task BeforeSleep(CancellationToken cancellationToken);
 
     /// <summary>
     /// Called after the platform returns to Wake state
     /// </summary>
     /// <param name="cancellationToken"></param>
-    /// <returns></returns>
     public Task AfterWake(CancellationToken cancellationToken);
 }

Source/Meadow.Contracts/Platform OS/IPlatformOS.Configuration.cs

@@ -229,5 +229,10 @@ public enum NetworkConnectionType
         /// </summary>
         /// <remarks>This should be a semicolon list of pin names that will be reserved for OS use.</remarks>
         public string ReservedPins { get; }
+
+        /// <summary>
+        /// Gets a list of NTP servers used for time synchronization
+        /// </summary>
+        public string[] NtpServers { get; }
     }
 }