异或校验和算法

在数据传输或者数据下载过程中，通常要保证数据的可靠性和安全性，所以，发送方和接收方要约定共同的协议，而这个协议中常常会出现校验和的运算。

C代码如下：

 1 unsigned char calc_nmea_checksum(const char * setence)
 2 {
 3     unsigned char checksum = 0;
 4     while(* setence)
 5     {
 6         checksum ^= (unsigned char)* setence++;
 7     }
 8
 9     return checksum;
10 }

实际应用代码

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.IO;
using System.IO.Ports;
using System.Threading;
using System.Diagnostics;
namespace serialport
{
    public partial class MainForm : Form
    {
        //      public Thread threadReceive = null;
        string Download_path = null;
        public static SerialPort com = null;
        public static int serialIndex = 0;
        public static int baudrateIndex = 1;
        public static string PortName = "com1";
        public static int BaudRate = 9600;
        bool IsTryToClosePort = false;
        bool IsReceiving = false;
        StringBuilder line_buffer = new StringBuilder(255);
        enum line { wait_start, wait_cr, wait_lf };
        int line_status = (int)line.wait_start;
        public static MainForm formMain;
        byte[] write_buffer = new byte[227];
        bool isFileOpen = false;
        FileStream fs;
        bool isPackWriten = false;
        //byte[] buffer = new byte[216];
        int count = 0;
        int tmpnum = 0;
        int receive_count = 0;
        byte[] result = new byte[] { 0x04, 0x24, 0x0C, 0x00, 0x02, 0x00, 0x01, 0x00, 0x01, 0x0E, 0x0D, 0x0A };
        byte[] receive_buffer = new byte[12];

        public MainForm()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            formMain = this;
            //IsMdiContainer = true;
            com = new SerialPort();
            com.DataBits = 8;
            com.DataReceived += new SerialDataReceivedEventHandler(com_DataReceived);

            FileStream fs;
            try
            {
                string fold = System.Environment.GetFolderPath(System.Environment.SpecialFolder.MyDocuments) + "\\BDTestTools.ini";
                fs = new FileStream(fold, FileMode.Open);
                try
                {
                    StreamReader sr = new StreamReader(fs, System.Text.Encoding.Default);
                    serialIndex = int.Parse(sr.ReadLine());
                    baudrateIndex = int.Parse(sr.ReadLine());
                    PortName = sr.ReadLine();
                    BaudRate = int.Parse(sr.ReadLine());
                    Download_path = sr.ReadLine();

                }
                catch (Exception ex)
                {
                    MessageBox.Show(ex.Message);
                }
                finally
                {
                    fs.Close();
                }
            }
            catch (Exception ex)
            {
                try
                {
                    string fold = System.Environment.GetFolderPath(System.Environment.SpecialFolder.MyDocuments) + "\\BDTestTools.ini";
                    fs = new FileStream(fold, FileMode.Create);
                    StreamWriter sw = new StreamWriter(fs);
                    sw.WriteLine(serialIndex.ToString());
                    sw.WriteLine(baudrateIndex.ToString());
                    sw.WriteLine(PortName);
                    sw.WriteLine(BaudRate.ToString());
                    sw.WriteLine(Download_path);

                    sw.Close();
                }
                catch (Exception ex1)
                {
                    MessageBox.Show(ex1.Message);
                }
            }
            label2.Text = PortName + ":" + BaudRate.ToString();

        }

        private void com_DataReceived(object sender, SerialDataReceivedEventArgs e)
        {
            if (IsTryToClosePort)
            {
                return;
            }
            if (!isPackWriten)
                return;
            while (receive_count < 12)
            {
                int n = com.BytesToRead;
                if (n == 0)
                    return;
                com.Read(receive_buffer, receive_count, 1);
                if (receive_buffer[receive_count] == result[receive_count])
                    receive_count++;

                 for (int i = 0; i < 5000; i++) ;

            }

            if (!WritePack())
            {
                write_buffer[6] = 0xff;
                write_buffer[7] = 0xff;
                Array.Clear(write_buffer, 8, 219);
                int checksum = 0;
                for (int i = 2; i < 224; i++)
                {
                    checksum ^= write_buffer[i];
                }
                write_buffer[224] = (byte)checksum;
                write_buffer[225] = 0x0d;
                write_buffer[226] = 0x0a;
                com.Write(write_buffer, 0, 227);

                fs.Close();
                isPackWriten = false;
                com.Close();
                MessageBox.Show("下载完成");

            }
        }

        private void ComToolStripMenuItem_Click(object sender, EventArgs e)
        {
            SetComForm formSetCom = new SetComForm();
            formSetCom.ShowDialog();
        }

        private void FileToolStripMenuItem_Click(object sender, EventArgs e)
        {
            string file;
            OpenFileDialog fileDialog = new OpenFileDialog();
            fileDialog.FileName = Download_path;
            fileDialog.Filter = "EPO文件|*.EPO";
            if (fileDialog.ShowDialog() == DialogResult.OK)
            {
                isFileOpen = false;

                file = fileDialog.FileName;
                try
                {
                    fs = new FileStream(file, FileMode.Open, FileAccess.Read);
                    fs.Close();
                    Download_path = file;
                    try
                    {
                        string fold = System.Environment.GetFolderPath(System.Environment.SpecialFolder.MyDocuments) + "\\BDTestTools.ini";
                        fs = new FileStream(fold, FileMode.Create);
                        StreamWriter sw = new StreamWriter(fs);
                        sw.WriteLine(serialIndex.ToString());
                        sw.WriteLine(baudrateIndex.ToString());
                        sw.WriteLine(PortName);
                        sw.WriteLine(BaudRate.ToString());

                       //label3.Text = Download_path;

                        sw.WriteLine(Download_path);
                        sw.Flush();

                        sw.Close();
                    }
                    catch (Exception ex1)
                    {
                        MessageBox.Show(ex1.Message);
                    }

                }
                catch (Exception ex)
                {
                    fs.Close();
                    MessageBox.Show(ex.Message);
                }
            }
        }

        private void DownloadToolStripMenuItem_Click(object sender, EventArgs e)
        {
            try
            {
                fs = new FileStream(Download_path, FileMode.Open, FileAccess.Read);
            }
            catch (Exception ex)
            {
                fs.Close();
                MessageBox.Show(ex.Message);
                return;
            }
            if (MainForm.com.IsOpen)
            {
                IsTryToClosePort = true;
                while (IsReceiving)
                {
                    System.Windows.Forms.Application.DoEvents();
                }
                try
                {
                    MainForm.com.Close();
                    IsTryToClosePort = false;
                    //                    ConnectToolStripMenuItem1.Text = "连接";
                }
                catch (Exception ex)
                {
                    MessageBox.Show(ex.Message);
                }
            }
            else
            {
                com.PortName = PortName;
                com.BaudRate = BaudRate;
                //com.NewLine = "";
                try
                {
                    //打开串口
                    com.Open();
                    try
                    {
                        string fold = System.Environment.GetFolderPath(System.Environment.SpecialFolder.MyDocuments) + "\\BDTestTools.ini";
                        FileStream fs = new FileStream(fold, FileMode.OpenOrCreate);
                        StreamWriter sw = new StreamWriter(fs);
                        sw.WriteLine(serialIndex.ToString());
                        sw.WriteLine(baudrateIndex.ToString());
                        sw.WriteLine(PortName);
                        sw.WriteLine(BaudRate.ToString());
                        sw.WriteLine(Download_path);
                        sw.Close();
                        label2.Text = PortName + ":" + BaudRate.ToString();
                        //                        ConnectToolStripMenuItem1.Text = "断开";
                    }
                    catch (Exception ex1)
                    {
                        MessageBox.Show(ex1.Message);
                    }
                }
                catch (Exception ex)
                {
                    //捕获到异常信息，创建一个新的comm对象，之前的不能用了
                    //com = new SerialPort();
                    //现实异常信息给客户
                    MessageBox.Show(ex.Message);
                    fs.Close();
                    return;
                }
            }

            receive_count = 0;
            WriteBuadeRate();
            WritePack();

            //启动线程
            Thread fthread = new Thread(new ThreadStart(SleepT));
            fthread.Start();

            isPackWriten = true;
        }

        public static string ToHexString(byte[] bytes)
        {
            string hexString = string.Empty;
            if (null != bytes)
            {
                StringBuilder sb = new StringBuilder();
                for (int i = 0; i < bytes.Length; i++)
                {
                    sb.Append(bytes[i].ToString("X2") + ‘ ‘);
                }
                hexString = sb.ToString();
            }
            return hexString;
        }

        public static void WriteFile(string context)
        {

            FileStream f = new FileStream(@"D:\EPOdownload.LOG", FileMode.OpenOrCreate, FileAccess.Write);

            StreamWriter sw = new StreamWriter(f);

            sw.BaseStream.Seek(0, SeekOrigin.End);

            sw.WriteLine(context);

            sw.Flush();
            sw.Close();
            f.Close();
        }

        private void WriteBuadeRate()
        {

            byte[] buadeRate = new byte[] { 0x24, 0x50, 0x4D, 0x54, 0x4B, 0x32, 0x35, 0x33, 0x2C, 0x31, 0x2C, 0x30, 0x2A, 0x33, 0x37, 0x0D, 0x0A };
            try
            {
                com.Write(buadeRate, 0, 17);
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }

        }
        private bool WritePack()
        {

            if (fs.Read(write_buffer, 8, 216) == 0)
            {
                return false;
            }
            write_buffer[0] = 0x04;
            write_buffer[1] = 0x24;
            write_buffer[2] = 0xE3;
            write_buffer[3] = 0x00;
            write_buffer[4] = 0xD3;
            write_buffer[5] = 0x02;
            write_buffer[6] = (byte)count;
            write_buffer[7] = (byte)(count / 0x100);
            count++;

            int checksum = 0;
            for (int i = 2; i < 224; i++)
            {
                checksum ^= write_buffer[i];//校验和算法
            }
            write_buffer[224] = (byte)checksum;
            write_buffer[225] = 0x0d;
            write_buffer[226] = 0x0a;

            result[6] = write_buffer[6];
            result[7] = write_buffer[7];
            checksum = 0;
            for (int i = 2; i <= 8; i++)
            {
                checksum ^= result[i];
            }
            result[9] = (byte)checksum;
            try
            {
                com.Write(write_buffer, 0, 227);
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }

            receive_count = 0;
            // WriteFile(ToHexString(write_buffer));
            // WriteFile(ToHexString(result));

            return true;
        }

        //private void progressBar1_Click(object sender, EventArgs e)
        //{
        //   Thread fthread = new Thread(new ThreadStart(SleepT));
        //  fthread.Start();
        // }

        private delegate void SetPos(int ipos);

        private void SetTextMessage(int ipos)
        {
            if (this.InvokeRequired)
            {
                SetPos setpos = new SetPos(SetTextMessage);
                this.Invoke(setpos, new object[] { ipos });
            }
            else
            {
                this.label.Text = ipos.ToString() + "%";
                this.progressBar1.Value = Convert.ToInt32(ipos);
                this.label1.Text = "已下载";

            }
        }

        private void SleepT()
        {
            for (int i = 0; i < 500; i++)
            {
                System.Threading.Thread.Sleep(60);//没什么意思，单纯的执行延时
                SetTextMessage(100 * i / 500);
            }
        }
}