tbf/TBF/Telegram.cs

///
/// Copyright (c) 2013-2015 Sensus Metering Systems
///
using System;
using System.Collections.Generic;
using System.Text;

namespace TBF
{
	public class Telegram
	{
		const UInt16 crcSeed = 0xFFFF;		// Initial crc value
		const UInt16 crcGP = 0xA001;		// Generating polynomial

		/// <summary>
		/// For standard CRC16 (remainder of division)
		/// to start a new crc, set CRC16 = SEED
		/// then for each byte call UpdateCRC(byte, &CRC16);
		/// CRC16 will contain the result
		/// (if you calculate all of the incoming data
		/// INCLUDING the crc, the result should be 0x0000
		/// and if you are sending the crc be sure to
		/// send the bytes in the correct order)
		/// <summary>
		static void UpdateCRC(byte b, ref UInt16 crc)
		{
			crc ^= (UInt16)b;
			for (int i = 0; i < 8; i++)
			{
				bool carry = (crc & 0x0001) != 0;
				crc >>= 1;
				if (carry) crc ^= crcGP;
			}
		}

		/// <summary>
		/// Calculates the CRC from a data telegram (an array of bytes).
		/// A complete telegram including two bytes reserved for the CRC
		/// must be supplied as an argument.
		/// </summary>
		/// <param name="data">Data telegram</param>
		/// <returns>Calculated CRC</returns>
		public static UInt16 ClaculateTelegramCRC(byte[] data)
		{
			UInt16 crc = crcSeed;
			for (int i = 0; i < data.Length - 2; i++) UpdateCRC(data[i], ref crc);
			return crc;
		}

		/// <summary>
		/// This function modifies the last 2 bytes in the message buffer
		/// by the CRC calculated from the remaining first (Lenght - 2) bytes.
		/// A complete telegram including two bytes reserved for the CRC
		/// must be supplied as an argument.
		/// </summary>
		/// <param name="data">Data telegram</param>
		public static void UpdateTelegramCRC(byte[] data)
		{
			int len = data.Length;
			if (len < 2) return;

			UInt16 crc = ClaculateTelegramCRC(data);

			data[len - 2] = (byte)(crc & 0xFF);
			data[len - 1] = (byte)(crc >> 8);
		}

		/// <summary>
		/// This function compares the last 2 bytes in the message buffer
		/// with the CRC calculated from the remaining first (Lenght - 2) bytes.
		/// A complete telegram including two bytes reserved for the CRC
		/// must be supplied as an argument.
		/// </summary>
		/// <param name="data">Data telegram</param>
		/// <returns>true if the CRC in the telegram is correct</returns>
		public static bool VerifyTelegramCRC(byte[] data)
		{
			int len = data.Length;
			if (len < 2) return false;

			UInt16 crc = ClaculateTelegramCRC(data);

			return (data[len - 2] == (byte)(crc & 0xFF)) && (data[len - 1] == (byte)(crc >> 8));
		}



		/// <summary>
		/// Calculates the checksum from a data telegram (an array of bytes).
		/// A complete telegram including one bytes reserved for the checksum
		/// must be supplied as an argument.
		/// </summary>
		/// <param name="data">Data telegram</param>
		/// <returns>Calculated CRC</returns>
		public static byte ClaculateTelegramChecksum(byte[] data)
		{
			byte checksum = 0;
			for (int i = 0; i < data.Length - 1; i++) checksum = (byte)(checksum ^ data[i]);
			return checksum;
		}

		/// <summary>
		/// This function modifies the last byte in the message buffer
		/// by the checksum calculated from the remaining first (Lenght - 1) bytes.
		/// A complete telegram including one bytes reserved for the checksum
		/// must be supplied as an argument.
		/// </summary>
		/// <param name="data">Data telegram</param>
		public static void UpdateTelegramChecksum(byte[] data)
		{
			int len = data.Length;
			if (len < 1) return;
			data[len - 1] = ClaculateTelegramChecksum(data);
		}

		/// <summary>
		/// This function compares the last byte in the message buffer
		/// with the checksum calculated from the remaining first (Lenght - 1) bytes.
		/// A complete telegram including two bytes reserved for the checksum
		/// must be supplied as an argument.
		/// </summary>
		/// <param name="data">Data telegram</param>
		/// <returns>true if the CRC in the telegram is correct</returns>
		public static bool VerifyTelegramChecksum(byte[] data)
		{
			int len = data.Length;
			if (len < 1) return false;
			return (data[len - 1] == ClaculateTelegramChecksum(data));
		}



		public static string LogTelegram(string intro, byte[] data)
		{
			System.Text.StringBuilder sb = new System.Text.StringBuilder(80);

			sb.Append(intro);
			sb.Append(data.Length.ToString());
			sb.Append(" bytes:");
			foreach (var d in data)
			{
				sb.Append(" ");
				sb.Append(((int)d).ToString("X2"));
			}

			return sb.ToString();
		}



		public static string LogTelegram(string intro, string data)
		{
			System.Text.StringBuilder sb = new System.Text.StringBuilder(80);

			sb.Append(intro);
			sb.Append(data.Length.ToString());
			sb.Append(" bytes:");
			foreach (var d in data)
			{
				sb.Append(" ");
				sb.Append(((int)d).ToString("X2"));
			}

			return sb.ToString();
		}
	}
}