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。
# 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。
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()))
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:
serial.Serial
实例)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:
COM2
。COM2
很忙,并为这个USB设备指定了一个不同的名称。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。
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()
或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:
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。
https://stackoverflow.com/questions/14525977
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