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社区首页 >问答首页 >如何使用serialException从pySerial中恢复

如何使用serialException从pySerial中恢复
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Stack Overflow用户
提问于 2013-01-25 16:24:21
回答 2查看 12.8K关注 0票数 12

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来促进这种交流。一切正常工作,直到USB电缆从PC上拔出并抛出异常为止。一旦电缆插入,我似乎无法恢复和重新连接到我的设备。唯一的办法,我恢复是关闭应用程序,并拔掉和插入电缆再次。任何帮助,以了解发生了什么,将是非常感谢。

这是我用来帮助我理解过程的基本测试代码。

代码语言:javascript
运行
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# 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"

UPDATE:下面是序列化Win32.py中creatfile()的代码,它返回以下消息: serial.serialutil.SerialException:未能打开端口COM5: Error 2系统找不到指定的文件。

代码语言:javascript
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    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())) 
EN

回答 2

Stack Overflow用户

发布于 2014-10-01 14:21:43

假设您的设备性能良好,您所必须做的就是:

  • 关闭您的串口(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。在您的例子中,会发生以下情况:

  • USB设备已连接并指定名称为COM2
  • 您的程序打开设备。
  • USB断开
  • 在程序注意到设备失效之前,USB会很快重新连接。
  • Windows会看到COM2很忙,并为这个USB设备指定了一个不同的名称。
  • (可选)程序关闭设备
  • 您的程序再次尝试打开COM2,但是没有该名称的硬件

绕过Windows聪明的方法--你可以在设备管理器,COM端口,端口,高级选项中为这个设备特别指定固定的COMX名称。

另一种选择是快速检测设备死机并关闭文件句柄。如果你是幸运的,那么当设备重新连接的时候,原来的COM2又是免费的。

另一个选择是使用另一个使用另一个驱动程序的制造商的USB串行转换器。不知怎么的,COMX的字母分配是特定于驱动程序的.更好的司机可能给你一个稳定的名字。

票数 3
EN

Stack Overflow用户

发布于 2015-08-13 14:06:10

我也遇到过这个问题。有时,当设备再次插入时,我的程序就会被锁定。

NB. i已经固定了@qarma中提到的端口的COMx名称。

我已经重新安排了我的程序,以便一旦从read()write()方法的Serial中抛出异常,我就停止调用这些方法。

然后,我有一个函数,它定期重新尝试打开端口,尝试检测设备何时再次插入。

此函数使用与原始函数相同的参数创建一个新的Serial实例,并尝试打开它:

代码语言:javascript
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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表示端口再次出现。

票数 1
EN
页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接:

https://stackoverflow.com/questions/14525977

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