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我有一个应用程序可以读取数据并将其传输到通过 USB 连接的设备。我正在使用 pySerial 来促进这种交流。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重新插入电缆。任何有助于理解正在发生的事情将不胜感激。

这是我用来帮助我理解该过程的基本测试代码。

# 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。

    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()))
4

2 回答 2

3

假设您的设备运行良好，您所要做的就是：

  • 关闭你的串口（serial.Serial实例）
  • 再次找到您的端口的 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：

  • USB 设备已连接并分配了名称COM2
  • 您的程序打开设备
  • USB 断开连接
  • 在您的程序注意到设备死机之前，USB 会快速重新连接
  • Windows 发现它COM2很忙，并为此 USB 设备分配了不同的名称
  • （可选）您的程序关闭设备
  • 您的程序尝试COM2再次打开，但该名称没有硬件

巧妙地绕过 Windows 的方法是——您可以COMX在设备管理器、COM 端口、您的端口、高级选项中专门为该设备分配固定名称。

另一种选择是快速检测设备死机并关闭文件句柄。如果你很幸运，那么到设备重新连接时，原始设备COM2将再次免费。

另一种选择是使用来自另一个制造商的 USB 串行转换器，该制造商使用另一个驱动程序。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。

于 2014-10-01T14:21:43.647 回答
1

我也遇到过这个问题。有时再次插入设备时我的程序已锁定。

注意。我已经修复了COMx@qarma 提到的端口名称

我重新安排了我的程序，以便一旦从read()或write()方法抛出异常，Serial我就停止调用这些方法。

然后我有一个功能，它会定期重试打开端口以尝试检测设备何时再次插入。

此函数创建一个Serial与原始实例具有相同参数的新实例并尝试打开它：

def try_to_open_new_port(self):
    ret = False
    test = serial.Serial(baudrate=9600, timeout=0, writeTimeout=0)
    test.port = self.current_port_name
    try:
        test.open()
        if test.isOpen():
            test.close()
            ret = True
    except serial.serialutil.SerialException:
        pass
    return ret

返回True表示该端口再次存在。

于 2015-08-13T14:06:10.383 回答