fix(#1686): throw an argument out range exception if gpio port is not in allowed range

Author: MrCSharp22

README.md

@@ -73,6 +73,10 @@ using var rxChannel = new ReceiverChannel(rxChannelSettings);
 rxChannel.Start(clearBuffer: true);
 ```
 
+## GPIO Pin Restrictions
+
+The ESP32 MCU restricts which GPIO pins can be used for the Transmit Channel (TX). Ports 34 to 39 (inclusive) cannot be used for TX. Attempting to use these ports will cause the `TransmitChannelSettings` class to throw an `ArgumentOutOfRangeException`.
+
 ## Build status
 
 | Component | Build Status | NuGet Package |

nanoFramework.Hardware.Esp32.Rmt/TransmitChannelSettings.cs

@@ -144,8 +144,15 @@ public TransmitChannelSettings(int pinNumber) : this(channel: -1, pinNumber)
         /// <param name="channel">The channel number to use. Valid value range is 0 to 7 (inclusive).</param>
         /// <param name="pinNumber">The GPIO Pin number to use with the channel.</param>
         /// <exception cref="ArgumentOutOfRangeException"><paramref name="channel"/> must be between 0 and 7.</exception>
+        /// <exception cref="ArgumentOutOfRangeException"><paramref name="pinNumber"/> must not be between 34 and 39.</exception>"
         public TransmitChannelSettings(int channel, int pinNumber) : base(channel, pinNumber)
         {
+            // ESP32 RMT TX channels cannot use GPIO pins 34-39
+            if (pinNumber >= 34 && pinNumber <= 39)
+            {
+                throw new ArgumentOutOfRangeException();
+            }
+
             _enableCarrierWave = true;
             _carrierLevel = true;
             _carrierWaveFrequency = 38_000;