Initial commit

src/NfcAime.Dll/PN532/Pn532HsuFrame.cs

@@ -0,0 +1,63 @@
+using System;
+
+namespace NfcAime.Dll.PN532 {
+    internal static class Pn532HsuFrame
+    {
+        public const byte Preamble = 0x00;
+        public const byte StartCode1 = 0x00;
+        public const byte StartCode2 = 0xFF;
+        public const byte Postamble = 0x00;
+
+        public const byte HostToPn532Tfi = 0xD4;
+        public const byte Pn532ToHostTfi = 0xD5;
+
+        public static readonly byte[] AckFrame =
+        [
+            0x00, 0x00, 0xFF, 0x00, 0xFF, 0x00
+        ];
+
+        public static readonly byte[] NakFrame =
+        [
+            0x00, 0x00, 0xFF, 0xFF, 0x00, 0x00
+        ];
+
+        public static byte[] BuildDataFrame(byte tfi, ReadOnlySpan<byte> data)
+        {
+            if (data.Length + 1 > byte.MaxValue)
+            {
+                throw new ArgumentOutOfRangeException(nameof(data), "PN532 HSU frames must fit in 255 bytes.");
+            }
+
+            var length = (byte)(data.Length + 1);
+            var lcs = ComputeLcs(length);
+            var dcs = ComputeDcs(tfi, data);
+
+            var frame = new byte[7 + length];
+            frame[0] = Preamble;
+            frame[1] = StartCode1;
+            frame[2] = StartCode2;
+            frame[3] = length;
+            frame[4] = lcs;
+            frame[5] = tfi;
+            data.CopyTo(frame.AsSpan(6));
+            frame[6 + data.Length] = dcs;
+            frame[7 + data.Length] = Postamble;
+
+            return frame;
+        }
+
+        public static byte ComputeLcs(byte length)
+            => (byte)((0x100 - length) & 0xFF);
+
+        public static byte ComputeDcs(byte tfi, ReadOnlySpan<byte> data)
+        {
+            var sum = tfi;
+            for (var index = 0; index < data.Length; index++)
+            {
+                sum += data[index];
+            }
+
+            return (byte)((0x100 - (sum & 0xFF)) & 0xFF);
+        }
+    }
+}