From 0716f17df5cb0d5849bb522fe35d2eba3427059a Mon Sep 17 00:00:00 2001
From: jdbruner <jdbruner@users.noreply.github.com>
Date: Sun, 12 Feb 2023 05:05:49 -0800
Subject: [PATCH] MFRC522 NFC transceiver support for Write16Bytes (#2027)

Mifare Write16Bytes, which is used by Mifare Classic and Mifare Ultralight (where it is called
"compatibility write") requires two writes to the card. The first one transfers the
block number, and the second contains the data to be written. Changed the Transceive
function to handle Write16Bytes the same as counter increment, decrement, and restore
(which also require two writes to the card).
---
 src/devices/Mfrc522/Mfrc522.cs | 18 ++++++++++--------
 1 file changed, 10 insertions(+), 8 deletions(-)

diff --git a/src/devices/Mfrc522/Mfrc522.cs b/src/devices/Mfrc522/Mfrc522.cs
index 812b8b0e..e661681b 100644
--- a/src/devices/Mfrc522/Mfrc522.cs
+++ b/src/devices/Mfrc522/Mfrc522.cs
@@ -867,6 +867,8 @@ namespace Iot.Device.Mfrc522
             // Use built in functions for authentication in case of classic Mifare cards
             if ((dataToSend[0] == (byte)MifareCardCommand.AuthenticationA) || (dataToSend[0] == (byte)MifareCardCommand.AuthenticationB))
             {
+                // UltralightCommand.GetVersion has the same command code as MifareCardCommand.AuthenticationA
+                // GetVersion returns data; AuthenticationA does not
                 if ((dataFromCard == null) || (dataFromCard.Length == 0))
                 {
                     status = SendAndReceiveData(MfrcCommand.MifareAuthenticate, dataToSend.ToArray(), null);
@@ -874,15 +876,14 @@ namespace Iot.Device.Mfrc522
                 else
                 {
                     return SendWithCrc(dataToSend, dataFromCard);
-
                 }
 
                 return status == Status.Ok ? 0 : -1;
             }
             else if ((dataToSend[0] == (byte)MifareCardCommand.Incrementation) || (dataToSend[0] == (byte)MifareCardCommand.Decrementation)
-                || (dataToSend[0] == (byte)MifareCardCommand.Restore))
+                || (dataToSend[0] == (byte)MifareCardCommand.Restore || (dataToSend[0] == (byte)MifareCardCommand.Write16Bytes)))
             {
-                return TwoStepsIncDecRestore(dataToSend, dataFromCard);
+                return TwoStepsWrite16IncDecRestore(dataToSend);
             }
             else if (Enum.IsDefined(typeof(UltralightCommand), (UltralightCommand)dataToSend[0]))
             {
@@ -942,7 +943,7 @@ namespace Iot.Device.Mfrc522
             return 0;
         }
 
-        private int TwoStepsIncDecRestore(ReadOnlySpan<byte> dataToSend, Span<byte> dataFromCard)
+        private int TwoStepsWrite16IncDecRestore(ReadOnlySpan<byte> dataToSend)
         {
             Status status;
             Span<byte> toSendFirst = stackalloc byte[4];
@@ -952,17 +953,18 @@ namespace Iot.Device.Mfrc522
             status = SendAndReceiveData(MfrcCommand.Transceive, toSendFirst.ToArray(), null);
             if (status != Status.Ok)
             {
-                _logger.LogWarning($"{nameof(TwoStepsIncDecRestore)} - Error {(MfrcCommand)dataToSend[0]}");
+                _logger.LogWarning($"{nameof(TwoStepsWrite16IncDecRestore)} - Error {(MfrcCommand)dataToSend[0]}");
                 return -1;
             }
 
             Span<byte> toSendSecond = stackalloc byte[dataToSend.Length];
+            int dataLength = toSendSecond.Length - 2;
             dataToSend.Slice(2).CopyTo(toSendSecond);
-            CalculateCrc(toSendSecond.Slice(0, 2), toSendSecond.Slice(2, 2));
+            CalculateCrc(toSendSecond.Slice(0, dataLength), toSendSecond.Slice(dataLength, 2));
 
-            status = SendAndReceiveData(MfrcCommand.Transceive, toSendSecond.ToArray(), dataFromCard);
+            status = SendAndReceiveData(MfrcCommand.Transceive, toSendSecond.ToArray(), null);
 
-            return status == Status.Ok ? dataFromCard.Length : -1;
+            return status == Status.Ok ? 0 : -1;
         }
 
         /// <inheritdoc/>
-- 
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