C#为什么Serial.WriteLine()这么慢？

Question

当我想给一个小小的3.5微控制器编程时，我会通过一个硬件串口发送一个.HEX文件给它。我有两种方法；一种方法是使用像Tera Term这样的串行通信应用程序来发送文件，另一种方法是通过我编写的一个小型C#命令行应用程序来做同样的事情。

当我向微控制器发送一个3000+行十六进制文件时，大约需要14秒。当我用我的C#程序做同样的事情时，它需要两倍的时间(或者更长！)。Tera Term和我的C#程序的波特率是相同的，当然，这两个程序的设置都很简单。当我使用数字示波器查看串行传输时，我看到了以下内容(两张照片中的时间刻度相同)：

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第一张照片显示了使用Tera Term时的传输，第二张照片显示了使用我的C#程序使用Serial.WriteLine()逐行传输文件内容时的传输，如下所示：

using System;
using System.IO;
using System.IO.Ports;
using System.Threading;
using System.Timers;
using System.Diagnostics;

/*
Small console app to facilitate over-the-air (OTA) updates to a Teensy 3.x/4.x controller,
using VS2019 with the Visual Micro extension as the Arduino IDE. It is called by a post-build
'hook' statement in a file called 'board.txt' located in whatever Teensy program is 
being updated.  This app does the following:

 - Extract the project path and selected COMPORT number from the arguments to the call to Main()
 - Opens a UART serial port connection to the Teensy, typically one provided by a BT adaptor
   operating in 'pass-through' mode. The serial port COMPORT number is passed into this app
   as an argument.
 - Sends whatever command is required to put the existing Teensy firmware into 'update' mode
 - Using the path of the updating program (passed in as an argument), locates the .HEX file 
   associated with the project, and sends it's contents to the Teensy, one line at a time, counting
   lines and confirming checksums line-by-line
 - Compares the number of lines sent to the Teensy with the number of lines received by the Teensy,
   and if there is a match, allows the Teensy update process to complete; otherwise aborts
*/

namespace TeensyFlash
{  
    class Program
    {
        const string startCmdStr = "U"; //used in sketch's 'GetUserInput()' to start upload sequence
        static string rcvStr = string.Empty;
        private static System.Timers.Timer aTimer;
        private static bool bTimedOut;

        static void Main(string[] args)
        {
            //Extract the build path and selected COMPORT number from the arguments to the call to Main()
            Console.WriteLine("Teensy Flash Console");
            Console.WriteLine("Number of arguments in args = {0}\n", args.Length);
            int argindex = 0;
            string comPortStr = string.Empty;
            foreach (var item in args)
            {
                Console.WriteLine(item);
                if (item.Contains("COM"))
                {
                    comPortStr = args[argindex];
                }

                argindex++;
            }

            string build_path = args[0];
            string projectName = args[args.Length - 1];
            projectName = projectName.Substring(0, projectName.Length - 4); //remove extension
            build_path = build_path.Replace("\"", string.Empty).Trim();
            string hexfilename = build_path + "\\" + projectName + ".hex";
            Console.WriteLine("path = {0}", build_path);
            Console.WriteLine("comport = {0}", comPortStr);
            Console.WriteLine("build name = {0}", projectName);
            Console.WriteLine("path to HEX file = {0}", hexfilename);

            try
            {
                Stopwatch stopwatch = Stopwatch.StartNew();
                string[] lines = System.IO.File.ReadAllLines(hexfilename);
                foreach (string item in lines)
                {
                    Console.WriteLine(item);
                }

                Console.WriteLine("this took " + stopwatch.ElapsedMilliseconds + " Msec");



            }
            catch (Exception)
            {

                throw;
            }

            Console.WriteLine("Opening Serial Port...");

            try
            {
                SerialPort _serport = new SerialPort(comPortStr, 115200);
                _serport.WriteTimeout = 1000;
                _serport.WriteBufferSize = 20480;
                _serport.Open();
                _serport.DiscardOutBuffer();
                _serport.DiscardInBuffer();
                Thread.Sleep(100);


                Console.WriteLine("Sending Trigger Character " + startCmdStr);
                Console.WriteLine(startCmdStr);
                _serport.Write(startCmdStr);


                Console.WriteLine("Waiting for 'waiting' from Teensy...");
                rcvStr = string.Empty;
                aTimer = new System.Timers.Timer();
                //aTimer.Interval = 5000;
                aTimer.Interval = 25000;
                aTimer.Elapsed += OnTimedEvent;

                aTimer.Start();
                
                while (!rcvStr.Contains("waiting") && !bTimedOut)
                {
                    if (_serport.BytesToRead > 0)
                    {
                        rcvStr = _serport.ReadLine();
                    }
                }
                aTimer.Stop();

                if (bTimedOut)
                {
                    Console.WriteLine("Timed out waiting for 'waiting' response from Teensy");
                }
                else
                {
                    //if we get to here, the Teensy is ready to receive HEX file contents
                    Console.WriteLine("Received " + rcvStr + " from Teensy");
                     
                    Stopwatch stopwatch2 = Stopwatch.StartNew();
                    int numlines = 0;
                    string[] lines = System.IO.File.ReadAllLines(hexfilename);
                    foreach (string item in lines)
                    {
                        numlines++;
                        _serport.WriteLine(item);
                    }
                    Console.WriteLine("total lines = {0}, time = {1} mSec", numlines, stopwatch2.ElapsedMilliseconds);

                    //now we wait for Teensy to emit "hex file: xx lines xx bytes..." and then "enter xx to flash..."
                    aTimer.Start();
                    while (!rcvStr.Contains("hex file:") && !bTimedOut)
                    {
                        if (_serport.BytesToRead > 0)
                        {
                            rcvStr = _serport.ReadLine();
                        }
                    }
                    aTimer.Stop();
                    aTimer.Dispose();

                    if (bTimedOut)
                    {
                        Console.WriteLine("Timed out waiting for 'hex file' response from Teensy");
                    }
                    else
                    {
                        //extract number of lines from Teensy string, and compare with numlines.
                        //If they match, then send the number back to Teensy to complete the update.
                        //Otherwise, send '0' to abort

                        int colonIdx = rcvStr.IndexOf(':');
                        int lineIdx = rcvStr.IndexOf("lines");
                        string compareStr = rcvStr.Substring(colonIdx + 1, lineIdx - colonIdx - 1);
                        compareStr = compareStr.Trim();
                        int numTeensyLines = Convert.ToInt16(compareStr);

                        Console.WriteLine("sent {0} teensy replied {1}", numlines, numTeensyLines);
                        if (numTeensyLines == numlines)
                        {
                            Console.WriteLine("numlines {0} matches numTeensyLines {1} - send confirmation",
                                numlines, numTeensyLines);

                            _serport.WriteLine(compareStr);
                        }
                    }
                }
            }
            catch (Exception)
            {

                throw;
            }

            try
            {

                }
            catch (Exception)
            {

                throw;
            }
        }

        static string chksum(string input)
        {
            int TwosComplement(string s)
            {
                if (s.Length % 2 != 0)
                    throw new FormatException(nameof(input));

                var checksum = 0;

                for (var i = 0; i < s.Length; i += 2)
                {
                    var value = int.Parse(s.Substring(i, 2), System.Globalization.NumberStyles.AllowHexSpecifier);

                    checksum = (checksum + value) & 0xFF;
                }

                return 256 - checksum & 0xFF;
            }

            //return string.Concat(":", input, " ", TwosComplement(input).ToString("X2"));
            return TwosComplement(input).ToString("X2");
        }
        private static void SetTimer()
        {
            // Create a timer with a two second interval.
            aTimer = new System.Timers.Timer(2000);
            // Hook up the Elapsed event for the timer. 
            aTimer.Elapsed += OnTimedEvent;
            //aTimer.AutoReset = true;
            aTimer.Enabled = true;
        }

        private static void OnTimedEvent(Object source, ElapsedEventArgs e)
        {
            Console.WriteLine("The Elapsed event was raised at {0:HH:mm:ss.fff}",
                              e.SignalTime);
            bTimedOut = true;
        }
    }

}

实际执行文件传输的代码是：

Stopwatch stopwatch2 = Stopwatch.StartNew();
int numlines = 0;
string[] lines = System.IO.File.ReadAllLines(hexfilename);
foreach (string item in lines)
{
    numlines++;
    _serport.WriteLine(item);
}
Console.WriteLine("total lines = {0}, time = {1} mSec", numlines, stopwatch2.ElapsedMilliseconds);

当'_serport.WriteLine(item);‘行被注释掉时，报告的运行时间是0 mSec，正如预期的那样-因此'ReadAllLines()’步骤不是问题。

有没有人知道为什么'WriteLine(item)‘处理这么慢？

Answer 1

这取决于设备的方法本身的结构，但我在同一网站上找到了一个可以帮助你的查询和方法

stackoverflow: console writeline slow