From a91883eba4a52b1a8cedf30ea920c41acc10eb97 Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Wed, 1 Jul 2026 14:14:12 +0000
Subject: [PATCH 1/2] Initial plan


From 3345d4bd9eb7e07dce8caf47171f3401ba88413a Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Wed, 1 Jul 2026 14:18:05 +0000
Subject: [PATCH 2/2] Allow zero-length I2C Write to emit a Start/Stop bus
 transaction

---
 src/System.Device.Gpio/System/Device/I2c/I2cDevice.cs |  2 ++
 .../System/Device/I2c/UnixI2cBus.cs                   | 11 +++++++++++
 2 files changed, 13 insertions(+)

diff --git a/src/System.Device.Gpio/System/Device/I2c/I2cDevice.cs b/src/System.Device.Gpio/System/Device/I2c/I2cDevice.cs
index d43e745ba5..1c7dce159b 100644
--- a/src/System.Device.Gpio/System/Device/I2c/I2cDevice.cs
+++ b/src/System.Device.Gpio/System/Device/I2c/I2cDevice.cs
@@ -70,6 +70,8 @@ public virtual unsafe void WriteByte(byte value)
     /// <param name="buffer">
     /// The buffer that contains the data to be written to the I2C device.
     /// The data should not include the I2C device address.
+    /// An empty buffer generates a transaction on the bus (Start condition, device address and Stop
+    /// condition) without transferring any data byte, which some devices require to be woken up.
     /// </param>
     public abstract void Write(ReadOnlySpan<byte> buffer);
 
diff --git a/src/System.Device.Gpio/System/Device/I2c/UnixI2cBus.cs b/src/System.Device.Gpio/System/Device/I2c/UnixI2cBus.cs
index bd5ee325b5..2e8ee50701 100644
--- a/src/System.Device.Gpio/System/Device/I2c/UnixI2cBus.cs
+++ b/src/System.Device.Gpio/System/Device/I2c/UnixI2cBus.cs
@@ -121,6 +121,17 @@ internal unsafe void Write(int deviceAddress, ReadOnlySpan<byte> buffer)
             throw new ArgumentException($"{nameof(buffer)} length is too long.", nameof(buffer));
         }
 
+        if (buffer.Length == 0)
+        {
+            // An empty write still generates a transaction on the bus (Start condition, device
+            // address, Stop condition) without transferring any data byte. Some devices (e.g. the
+            // PN532 NFC reader) rely on this to be woken up. A non-null pointer is required so that
+            // WriteReadCore emits a zero-length write message instead of skipping it.
+            byte placeholder = 0;
+            WriteReadCore((ushort)deviceAddress, &placeholder, null, 0, 0);
+            return;
+        }
+
         fixed (byte* writeBufferPointer = buffer)
         {
             WriteReadCore((ushort)deviceAddress, writeBufferPointer, null, (ushort)buffer.Length, 0);