c# - 在字节 [] 中查找 MBUS 电报

Question

我正在尝试从串行端口读取 MBUS 电报。我将串口中的所有内容都放入一个字节数组中。

每个 MBUS 电报都以这种模式(十六进制)开头:68 XX XX 68
其中 XX 是以字节为单位的电报长度。

例子: Example http://img97.imageshack.us/img97/6004/mbustele.jpg

这里是一个示例，突出显示的是长度为 99(十六进制)的电报的开头

我想把每一个电报都添加到这样的列表中

List<byte[]> telegramms;

如何实现这个想法？

Answer 1

我刚刚在 VisualStudio 2010 中输入了这个，它对字节顺序做出了各种假设，并且没有管理 MBus 数据包大于串行端口采样字节的潜在问题，或者更重要的是, 如果数据包 header 本身跨越了来自串行端口的数据包之间的边界。

using System;
using System.Collections.Generic;
using System.Linq;
using Microsoft.VisualStudio.TestTools.UnitTesting;

namespace StackOverflowTest
{
    [TestClass]
    public class ByteTest
    {
        private bool FindEndMark(byte[] source, int index, out int size)
        {
            int endIndex = index + 3;
            if (endIndex > source.Count())
            {
                // need to cope with the fact that the datapacket might be shorter than the MBus message.
                throw new Exception("end count > length of array");
            }

        if (source[endIndex] == 0x68)
        {
            // According to the updated spec, the size is emitted twice as a verification
            if (source[index + 1] == source[index + 2])
            {
                size = source[index] + 1;
                return true;
            }
        }
            size = 0;
            return false;
        }

        [TestMethod]
        public void FindMbusDatagram()
        {
            byte[] src = new byte[]
                {
                    // Random junk to start
                    00, 01, 02, 03, 04, 05, 06, 07, 08, 09, 0xa, 0xb, 0xc, 0xd, 
                    // An MBus Packet
                    0x68, 06, 00, 0x68, 08, 05, 72, 00, 00, 00, 
                    // More junk
                    00, 00, 00, 0x16, 00, 00, 00, 00, 01, 
                    // Put a rogue 0x68 in so we can prove we don't get false positives in the datastream
                    0x68, 03, 04, 05, 06, 07, 08, 09, 0xa, 0xb, 0xc, 0xd,
                    // Another Packet
                    0x68, 01, 00, 0x68, 0xFF,
                    //final junk
                     00, 16, 00, 00, 00, 01, 02, 03
                };

            List<byte[]> packets = new List<byte[]>();

            for (int i = 0; i < src.Length; i++ )
            {
                if (src[i] != 0x68)
                {
                    continue;
                }
                else
                {
                    int packetSize = 0;
                    if (FindEndMark(src, i, out packetSize))
                    {
                        if (packetSize > (src.Length - i))
                        {
                            // read more data from your port and append it somehow.
                        }
                        else
                        {
                            // We're packetSize+4 includes the header information + checksum and end
                        // NB: packetSize+5 is a checksum byte
                        // NB: packetSize+6 should be 0x16 according to the MBus spec.
                            byte[] packet = new byte[packetSize + 4];
                            int count = 0;

                            // Copy the packet + header into a byte[]
                            for (int j = i; j < (i + packetSize + 4); j++)
                            {
                                packet[count++] = src[j];
                            }

                            packets.Add(packet);

                            // Move the counter along
                            i += (packetSize + 4);
                        }
                    }
                }
            }

            // Should have two packets here.
            Assert.IsTrue(packets.Count > 0);
        }
    }
}