如何使用 pySerial 从 serialException 中恢复

问题描述

我有一个应用程序可以读取数据并将数据传输到通过 USB 连接的设备.我正在使用 pySerial 来促进这种通信.一切正常，直到从 PC 上拔下 USB 电缆并引发异常.重新插入电缆后，我似乎无法恢复并重新连接到我的设备.我恢复的唯一方法是关闭应用程序并拔下并再次插入电缆.任何帮助了解正在发生的事情将不胜感激.

I have an application that reads and transmits data to a device connected via USB. I'm using pySerial to facilitate this communication. Everything works fine until the USB cable is unplugged from the PC and an exception is thrown. Once the cable is plugged back in, I can't seem to recover and reconnect to my device. The only way for me to recover is to close down the application and unplug and plug the cable in again. Any help in understanding what's going on would be much appreciated.

这是我用来帮助我理解过程的基本测试代码.

This is basic test code that I'm useing to help me understand the process.

# Class used to communicate with USB Dongle

import serial
import time
import sys

class LPort:
  def __init__(self, port=0):
    "initialize the LPort class"
    self.error = ""
    self.traffic = ""
    self.dest = None
    if port == None:
        self.simulation = True
    else:
        self.simulation = False
        self.port = port # serial port we should use
    self.reset()
    self.time = time.time()

def reInit(self):
    self.close()

def reset(self):
    "flush port, reset the LPort, initialize LPort"
    if self.simulation:
        r = "LPort simulator"
    else:
        self.port.flushInput()
        self.port.flushOutput()
        self.fail = False
        self.command("/H1")
        self.dest = None
        r = "reset"
    self.error = ""
    self.traffic = ""
    return r

def status(self):
    "return accumulated status info, reset collection"
    s = self.error
    self.error = ""
    return s

def data(self):
    "return accumulated traffic data, reset collection"
    s = self.traffic
    self.traffic = ""
    return s

def set_dest(self, addr):
    "set the destination address (if necessary)"
    if addr != self.dest:
        self.dest = addr
        self.command("/O")
        r = self.command("/D%02X" % addr)
        if r != "*":
            self.dest = None
            self.error += r
        else:
            r = True
    return r

def checksum(self, bytes):
    "calculate the CRC-8 checksum for the given packet"
    crc_table = [
            # this table is taken from the CP rectifier code
            0x00,0x07,0x0E,0x09,0x1C,0x1B,0x12,0x15,0x38,0x3F,
            0x36,0x31,0x24,0x23,0x2A,0x2D,0x70,0x77,0x7E,0x79,
            0x6C,0x6B,0x62,0x65,0x48,0x4F,0x46,0x41,0x54,0x53,
            0x5A,0x5D,0xE0,0xE7,0xEE,0xE9,0xFC,0xFB,0xF2,0xF5,
            0xD8,0xDF,0xD6,0xD1,0xC4,0xC3,0xCA,0xCD,0x90,0x97,
            0x9E,0x99,0x8C,0x8B,0x82,0x85,0xA8,0xAF,0xA6,0xA1,
            0xB4,0xB3,0xBA,0xBD,0xC7,0xC0,0xC9,0xCE,0xDB,0xDC,
            0xD5,0xD2,0xFF,0xF8,0xF1,0xF6,0xE3,0xE4,0xED,0xEA,
            0xB7,0xB0,0xB9,0xBE,0xAB,0xAC,0xA5,0xA2,0x8F,0x88,
            0x81,0x86,0x93,0x94,0x9D,0x9A,0x27,0x20,0x29,0x2E,
            0x3B,0x3C,0x35,0x32,0x1F,0x18,0x11,0x16,0x03,0x04,
            0x0D,0x0A,0x57,0x50,0x59,0x5E,0x4B,0x4C,0x45,0x42,
            0x6F,0x68,0x61,0x66,0x73,0x74,0x7D,0x7A,0x89,0x8E,
            0x87,0x80,0x95,0x92,0x9B,0x9C,0xB1,0xB6,0xBF,0xB8,
            0xAD,0xAA,0xA3,0xA4,0xF9,0xFE,0xF7,0xF0,0xE5,0xE2,
            0xEB,0xEC,0xC1,0xC6,0xCF,0xC8,0xDD,0xDA,0xD3,0xD4,
            0x69,0x6E,0x67,0x60,0x75,0x72,0x7B,0x7C,0x51,0x56,
            0x5F,0x58,0x4D,0x4A,0x43,0x44,0x19,0x1E,0x17,0x10,
            0x05,0x02,0x0B,0x0C,0x21,0x26,0x2F,0x28,0x3D,0x3A,
            0x33,0x34,0x4E,0x49,0x40,0x47,0x52,0x55,0x5C,0x5B,
            0x76,0x71,0x78,0x7F,0x6A,0x6D,0x64,0x63,0x3E,0x39,
            0x30,0x37,0x22,0x25,0x2C,0x2B,0x06,0x01,0x08,0x0F,
            0x1A,0x1D,0x14,0x13,0xAE,0xA9,0xA0,0xA7,0xB2,0xB5,
            0xBC,0xBB,0x96,0x91,0x98,0x9F,0x8A,0x8D,0x84,0x83,
            0xDE,0xD9,0xD0,0xD7,0xC2,0xC5,0xCC,0xCB,0xE6,0xE1,
            0xE8,0xEF,0xFA,0xFD,0xF4,0xF3]
    for i in range(len(bytes)):
        b = int(bytes[i])
        if i == 0: chksum = crc_table[b]
        else: chksum = crc_table[chksum ^ b]
    return chksum

def command(self, cmd):
    "transmit distinct commands to unit, and accept response"
    if self.simulation:
        r = "*"
    else:
        try:
            self.port.write(cmd + chr(13))
        except serial.serialutil.SerialTimeoutException:
            r = "/TO"
            return r
        except:
            print "Unexpected error:", sys.exc_info()[0]
            r = "/Unknown"
            return r
        r = ""
        eol = False
        while True:
            c = self.port.read(1)
            if not c:
                r = "/FAIL " + r + " " + cmd
                self.error = r
                break
            else:
                r += c
                ordc = ord(c)
                if ordc == 13 or ordc == 42:
                    break
    return r

def checkRawDataForErrors(self, raw, errors = []):

    errorCodes = {'/SNA':'Slave Not Acknowledging',
                    '/I81':'Busy, Command Ignored',
                    '/I88':'Connection Not Open',
                    '/I89':'Invalid Command Argument',
                    '/I8A':'Transmit Not Active',
                    '/I8F':'Invalid Command',
                    '/I90':'Buffer Overflow',
                    '/DAT':'Data Error',
                    '/BADPEC':'Bad PEC Value',
                    '/NO_MRC':'No Master Read Complete Signal',
                    '/FAIL':'General Failure',
                    '/LEN':'Data Length Error'}

    for ekey, eval in errorCodes.items():
        if ekey in raw:
            errors.append(eval)

    return errors
# self-testing module
if __name__ == "__main__":

  com = serial.Serial(port=4, baudrate=115200, timeout=1, xonxoff=0)

  if com:
    port = LPort(com)
    print port
    time.sleep(5)

    port = LPort(com)

    print "/V =", port.command("/V")
    print "/V", port.data(), port.status()
    print "/O =", port.command("/O")
    print "/O", port.data(), port.status()
    print "/A =", port.command("/A")
    print "/A", port.data(), port.status()
    print "/L =", port.command("/L")
    print "/L", port.data(), port.status()
    com.close()
else:
    print "cannot open com port"

更新:以下是 serialwin32.py 中 creatfile() 周围的代码，它返回以下消息:serial.serialutil.SerialException: 无法打开端口 COM5: [错误 2] 系统找不到指定的文件.

UPDATE:The following is the code around the creatfile() in serialwin32.py which returns the following message:serial.serialutil.SerialException: could not open port COM5: [Error 2] The system cannot find the file specified.

    self.hComPort = win32.CreateFile(port,
           win32.GENERIC_READ | win32.GENERIC_WRITE,
           0, # exclusive access
           None, # no security
           win32.OPEN_EXISTING,
           win32.FILE_ATTRIBUTE_NORMAL | win32.FILE_FLAG_OVERLAPPED,
           0)
    if self.hComPort == win32.INVALID_HANDLE_VALUE:
        self.hComPort = None    # 'cause __del__ is called anyway
        raise SerialException("could not open port %s: %s" % (self.portstr,  ctypes.WinError()))

推荐答案

假设您的设备表现良好，您必须做的就是:

Assuming your device is well-behaved, all you must do is this:

• 关闭你的串口(serial.Serial 实例)
• 再次查找端口的 COMX 名称
• 打开串口

第二部分是有问题的，因为 Windows 试图变得聪明.在您的情况下，会发生以下情况:

The 2nd part is problematic because Windows tries to be clever. In your case the following happens:

• USB 设备已连接并被分配名称 COM2
• 您的程序会打开设备
• USB 断开连接
• USB 在您的程序注意到设备死机之前快速重新连接
• Windows 发现 COM2 正忙，并为此 USB 设备分配了一个不同的名称
• (可选)您的程序会关闭设备
• 您的程序尝试再次打开 COM2，但没有该名称的硬件

• USB device is connected and is assigned name COM2
• Your program opens the device
• USB disconnects
• USB reconnects quickly before your program noticed that device died
• Windows sees that COM2 is busy and assigns a different name to this USB device
• (optional) your program closes the device
• your program tries to open COM2 again, but there's no hardware at that name

绕过 Windows 的方法很聪明——您可以在设备管理器、COM 端口、您的端口、高级选项中专门为此设备分配固定的 COMX 名称.

The are way to get around Windows being clever -- you can specifically assign fixed COMX name to this device in Device Manager, COM ports, your port, advanced options.

另一种选择是检测设备快速死亡并关闭文件句柄.如果你很幸运，那么当设备重新连接时，原始 COM2 又免费了.

Another option is to detect device dying very fast and closing the file handle. If you are lucky then by the time device reconnects original COM2 is free again.

另一种选择是使用使用其他驱动程序的其他制造商的 USB 串行转换器.不知何故，COMX 字母分配是特定于驱动程序的.更好的驱动程序可能会给你一个稳定的名字.

Yet another option is to use a USB-serial converter from another manufacturer that uses another driver. Somehow COMX letter assignment is driver-specific. Better drivers may give you a stable name.

这篇关于如何使用 pySerial 从 serialException 中恢复的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！