DummySPISlave: Add events and minor documentation

Added events so that DummySPISlave can be extended with user implementation. Reference taken from DummyI2CSlave.

Author: niranjanjoshi91

src/Emulator/Peripherals/Peripherals/Mocks/DummySPISlave.cs

@@ -1,15 +1,25 @@
-//
+//
 // Copyright (c) 2010-2021 Antmicro
 //
 //  This file is licensed under the MIT License.
 //  Full license text is available in 'licenses/MIT.txt'.
 //
+using System;
 using Antmicro.Renode.Logging;
 using Antmicro.Renode.Peripherals.SPI;
 using System.Collections.Generic;
 
 namespace Antmicro.Renode.Peripherals.Mocks
 {
+    /// <summary>
+    /// A dummy SPI slave peripheral implementing <see cref="ISPIPeripheral"> for mocking communication and testing SPI controllers.
+    /// Model supports queuing data to its buffer, that will be return upon SPI Transmit. Additionally it exposes events that allow mocking more complex models.
+    /// Example:
+    /// python """
+    ///     dummy = monitor.Machine["sysbus.spi.dummy"]
+    ///     dummy.DataReceived += lambda data: dummy.EnqueueValue(data)
+    /// """
+    /// </summary>
     public class DummySPISlave : ISPIPeripheral
     {
         public DummySPISlave()
@@ -33,8 +43,17 @@ public void Reset()
             idx = 0;
         }
 
+
+        /// <summary>
+        /// Implements <see cref="ISPIPeripheral">.
+        /// Logs the received <paramref name="data"/>.
+        /// </summary>
+        /// <remarks>
+        /// This method invokes <see cref="DataReceived"> event.
+        /// </remarks>
         public byte Transmit(byte data)
         {
+            DataReceived?.Invoke(data);
             this.Log(LogLevel.Debug, "Data received: 0x{0:X} (idx: {1})", data, idx);
             idx++;
             if(buffer.Count == 0)
@@ -45,8 +64,17 @@ public byte Transmit(byte data)
             return buffer.Dequeue();
         }
 
-        private int idx;
+        /// <summary>
+        /// Informs about the <see cref="Write"> method being called with the first argument being the data written to the model.
+        /// </summary>
+        public event Action<byte> DataReceived;
 
+        /// <summary>
+        /// Informs about the <see cref="FinishTransmission"> method being called.
+        /// </summary>
+        public event Action TransmissionFinished;
+
+        private int idx;
         private readonly Queue<byte> buffer;
     }
 }