在串行端口中并不总是检测到奇偶校验错误

Question

I have a serial port class in netcore - it just listens to the port and tries to detect parity errors. Parity is set to space, and all incoming bytes are being sent with parity=mark which should result in a parity error. Unfortunately, this is being detected only about a 1/3 of times. I need this detection because this is how the protocol states the beginning of a message. bytes (80 and 81) are being sent every 1 second so the buffer should always have 1 byte.

What am I doing wrong?

// Use this code inside a project created with the Visual C# > Windows Desktop > Console Application template.
// Replace the code in Program.cs with this code.

using System;
using System.Collections.Generic;
using System.IO.Ports;
using System.Threading;
using SASComms;

public class PortChat
{
    static bool _continue;
    static SASSerialPort _serialPort;
    static object msgsLock = new object();
    static Queue<byte[]> msgs = new Queue<byte[]>();
    static Queue<byte> receiveQeue = new Queue<byte>();
    public static void Main()
    {
        string name;
        string message;
        StringComparer stringComparer = StringComparer.OrdinalIgnoreCase;
        Thread readThread = new Thread(Read);

        // Create a new SerialPort object with default settings.
        _serialPort = new MachineSerialPort();

        // Allow the user to set the appropriate properties.
        _serialPort.PortName = "COM2";
        _serialPort.BaudRate = 19200;
        _serialPort.ParityReplace = (byte)'\0' ;
        _serialPort.ReadBufferSize = 128;
        _serialPort.Parity = Parity.Space;
        _serialPort.DataBits = 8;
        _serialPort.StopBits = StopBits.One;
        _serialPort.Handshake = Handshake.None;
        // Set the read/write timeouts
        _serialPort.ReadTimeout = 5;
        _serialPort.WriteTimeout = 5;
        _serialPort.ErrorReceived +=  new SerialErrorReceivedEventHandler(sp_SerialErrorReceivedEventHandler);

        _serialPort.Open();
        _continue = true;
        readThread.Start();
    }

    public static void sp_SerialErrorReceivedEventHandler(Object sender, SerialErrorReceivedEventArgs e)
    {
        if (e.EventType == SerialError.RXParity)
        {
            Console.WriteLine("Parity error");
        }
    }

    public static void Read()
    {
        while (_continue)
        {
            try
            {

                    while (_serialPort.BytesToRead > 0)
                    {
                     receiveQeue.Enqueue((byte)_serialPort.ReadByte());
                }

                if (receiveQeue.Count > 0)
                {
                    foreach (byte r in receiveQeue)
                    {
                        Console.Write(r.ToString("X")+" " );
                        Console.WriteLine();
                        }
                    }
                }
                receiveQeue.Clear();
            }
            catch (TimeoutException) { }
        }
    }
}

The console is outputing this:

80
Parity error
81
80
Parity error
81
Parity error
80
Parity error
81
80
Parity error
81
80
81
80
81
Parity error
80
Parity error
81
80
Parity error

And I'm expecting "Parity error" after each byte.

Answer 1

Achieved much better result by moving the read logic into the SerialError handler. Removed the Read() function and the readThread thread.

Answer 2

I had the exact same issue. I was getting only 30-50% of Mark bytes being flagged with parity errors. In my case the problem was the USB RS-232 Serial cable I was using. When I switched to true RS-232 over a DB-9 cable the serial errors were raised 100% correctly.