Make FT4222 I2C master clock frequency configurable

src/devices/Ft4222/Ft4222Device.cs

@@ -16,6 +16,12 @@ namespace Iot.Device.Ft4222
     /// </summary>
     public class Ft4222Device : FtDevice
     {
+        /// <summary>
+        /// Gets or sets the I2C master clock frequency in kbps used when creating an I2C bus.
+        /// Supported range is 60 to 3400 kbps. Defaults to 400 kbps.
+        /// </summary>
+        public uint I2cBusFrequencyKbps { get; set; } = Ft4222I2cBus.DefaultI2cMasterFrequencyKbps;
+
         /// <summary>
         /// Gets all the FT4222 connected
         /// </summary>
@@ -69,7 +75,7 @@ protected override I2cBusManager CreateI2cBusCore(int busNumber, int[]? pins)
                 throw new ArgumentOutOfRangeException(nameof(busNumber));
             }
 
-            return new I2cBusManager(this, busNumber, pins, new Ft4222I2cBus(this));
+            return new I2cBusManager(this, busNumber, pins, new Ft4222I2cBus(this, I2cBusFrequencyKbps));
         }
 
         /// <inheritdoc />

src/devices/Ft4222/Ft4222I2cBus.cs

@@ -18,11 +18,29 @@ namespace Iot.Device.Ft4222
     /// </summary>
     internal class Ft4222I2cBus : I2cBus
     {
-        private const uint I2cMasterFrequencyKbps = 400;
+        /// <summary>
+        /// The default I2C master clock frequency in kbps used when none is specified.
+        /// </summary>
+        public const uint DefaultI2cMasterFrequencyKbps = 400;
+
+        /// <summary>
+        /// The minimum I2C master clock frequency in kbps supported by the FT4222.
+        /// </summary>
+        public const uint MinimumI2cMasterFrequencyKbps = 60;
+
+        /// <summary>
+        /// The maximum I2C master clock frequency in kbps supported by the FT4222.
+        /// </summary>
+        public const uint MaximumI2cMasterFrequencyKbps = 3400;
 
         private readonly Dictionary<int, I2cDevice> _usedAddresses = new Dictionary<int, I2cDevice>();
         private SafeFtHandle _ftHandle;
 
+        /// <summary>
+        /// Gets the I2C master clock frequency in kbps used by this bus.
+        /// </summary>
+        public uint I2cMasterFrequencyKbps { get; }
+
         /// <summary>
         /// Store the FTDI Device Information
         /// </summary>
@@ -32,8 +50,16 @@ internal class Ft4222I2cBus : I2cBus
         /// Create a FT4222 I2C Device
         /// </summary>
         /// <param name="deviceInformation">Device information. Use FtCommon.GetDevices to get it.</param>
-        public Ft4222I2cBus(Ft4222Device deviceInformation)
+        /// <param name="i2cMasterFrequencyKbps">The I2C master clock frequency in kbps. Supported range is 60 to 3400 kbps.</param>
+        public Ft4222I2cBus(Ft4222Device deviceInformation, uint i2cMasterFrequencyKbps = DefaultI2cMasterFrequencyKbps)
         {
+            if (i2cMasterFrequencyKbps < MinimumI2cMasterFrequencyKbps || i2cMasterFrequencyKbps > MaximumI2cMasterFrequencyKbps)
+            {
+                throw new ArgumentOutOfRangeException(nameof(i2cMasterFrequencyKbps), $"I2C master clock frequency must be between {MinimumI2cMasterFrequencyKbps} and {MaximumI2cMasterFrequencyKbps} kbps.");
+            }
+
+            I2cMasterFrequencyKbps = i2cMasterFrequencyKbps;
+
             switch (deviceInformation.Type)
             {
                 case FtDeviceType.Ft4222HMode0or2With2Interfaces:

src/devices/Ft4222/README.md

@@ -94,6 +94,14 @@ if (bme280.TryReadTemperature(out Temperature temperature))
 }
 ```
 
+By default, the I2C bus is initialized at 400 kbps. You can change the I2C master clock frequency (supported range is 60 to 3400 kbps) by setting `I2cBusFrequencyKbps` on the `Ft4222Device` before creating the bus:
+
+```csharp
+Ft4222Device device = new Ft4222Device(FtCommon.GetDevices()[0]);
+device.I2cBusFrequencyKbps = 100;
+using I2cBus ftI2c = device.CreateI2cBus();
+```
+
 ### SPI
 
 ```Ft4222Spi``` is the SPI driver which you can pass later to any device requiring SPI or directly use it to send SPI commands. The SPI implementation is fully compatible with ```System.Device.Spi.SpiDevice```.