這個屬於我專案中一個函式，跟大家分享一下我的思路及最終實現

在編寫串列埠通訊工具中，需要實現一個函式，自動找到對應com 口，並且連線該com口，保證後續通訊正常
作為初始化過程的一部分。

思路

在win 裝置管理器中，經常會出現多個com 口，但並不是每個com 口都是目標裝置所連結的。
嘗試開啟每個com 口，輸入enter 按鍵， 正確的com 口，會有ack log 返回，表明通訊 正常

否則，沒有任何log 返回，則判斷為非目標裝置所連線的com 口。

實現

嘗試去開啟所有com 口，然後傳送enter， 如果在一段時間內有返回值，檢查com 口收到的位元組數，如果非零，則表明找到了對應的com 口。

完整測試程式碼如下：

import serial
import serial.tools.list_ports
import threading
import binascii
import time
from datetime import datetime

# default value
baunRate = 115200
is_read = False
is_write = False
write_buff = []
sys_buff = []
mSerial = None
callback = None
is_opened = 0
is_registed = 0


class SerialPort:

  def __init__(self,port,buand):

    self.port = serial.Serial(port,buand)
    self.port.close()
    if not self.port.isOpen():
      self.port.open()

    #the index of data_bytes for read operation,私有屬性
    #only used in read lines
    self.__read_ptr = 0
    self.__read_head = 0
    #store all read bytes
    # used in read date， read lines
    self.__data_bytes = bytearray()

  def port_open(self):
    if not self.port.isOpen():
      self.port.open()

  def port_close(self):
    self.port.close()

  def send(self):
    global is_write
    global write_buff

    while is_write:
      if len(write_buff):
        msg = write_buff.pop(0)
        msg = msg+"\n"
        cmd = msg.encode()
        try:

          self.port.write(cmd)
        except:
          write_buff.clear()
          is_write = False
    write_buff.clear()

  def read_data(self):
    global is_read
    global is_opened
    byte_cnt = 0
    while is_read:
      try:
        count = self.port.inWaiting()
        if count > 0:
          rec_str = self.port.read(count)
          self.__data_bytes = self.__data_bytes+rec_str
        #print("receive:",rec_str.decode())
          #print(rec_str)
          byte_cnt += count
          if not is_opened:
            is_opened = 1
      #print("累計收到：",byte_cnt)
      #time.sleep(0.5)
        self.read_lines()
      except:
        deinit()


  #將當前所有的資料都讀出，讀取位置不變，每次讀取指標依次移動，不漏資料， 讀取行為一直在進行
  def read_lines(self):
    #reset
    line_cnt = 0
    data_len = len(self.__data_bytes)
    #print ("")
    #print ("begin: prt=:",self.__read_ptr," head =",self.__read_head,"current len =",data_len)
    if self.__read_ptr >=data_len:
      return
    #get all lines in current data_bytes
    while(self.__read_ptr < data_len-1):
      if(self.__data_bytes[self.__read_ptr+1] == 0x0a and self.__data_bytes[self.__read_ptr] == 0x0d):
        tmp = bytearray()
        tmp = self.__data_bytes[self.__read_head:self.__read_ptr]

        try:
          line = tmp.decode()
        except:
          self.__read_head = self.__read_ptr + 2
          self.__read_ptr = self.__read_head
          continue
        iprint(line)
        line_cnt += 1
        self.__read_head = self.__read_ptr + 2
        self.__read_ptr = self.__read_head
      else:
        self.__read_ptr = self.__read_ptr + 1

def auto_open_serial():
  global baunRate
  global mSerial
  global callback
  global is_registed
  global is_opened
  #reset
  deinit()
  # 列出所有當前的com口
  port_list = list(serial.tools.list_ports.comports())
  port_list_name = []
  #get all com
  if len(port_list) <= 0:
    iprint("the serial port can't find!")
    return False
  else:
    for itms in port_list:
      port_list_name.append(itms.device)
  #try open
  #print(port_list_name)
  for i in port_list_name:
    try:
      mSerial = SerialPort(i,baunRate)
      iprint("try open %s"%i)
      start_task()
      send("")
      #return True
      time.sleep(1)
      if is_opened:
        iprint("connect %s successfully"%i)
        return True
      else:
        deinit()
        if i == port_list_name[len(port_list_name)-1]:
          iprint("uart don't open")
          break
        continue
    except:
      iprint(" uart don't open")
  deinit()
  return False

def deinit():
  global mSerial
  global is_write
  global is_read
  global write_buff
  global is_opened

  if mSerial:
    mSerial.port_close()

  is_opened = 0
  is_read = False
  is_write = False
  write_buff = []

  mSerial = None
  time.sleep(1)

def init():
  global mSerial
  global callback
  global is_registed
  global is_opened
  global is_read
  global is_write
  #retry
  retry_time = 0
  while not auto_open_serial():
    if not is_opened:
      iprint("wait for uart connect,retry %s"%str(retry_time))
    else:
      return True
    retry_time += 1
    time.sleep(2)
    if retry_time == 10:
      iprint(" open uart fail")
      return False

def send(msg):
  global mSerial
  global is_write
  global write_buff
  if is_write:
    write_buff.append(msg)

def start_task():
  global mSerial
  global is_write
  global is_read

  if mSerial:
    is_write = True
    t1 = threading.Thread (target=mSerial.send)
    t1.setDaemon (False)
    t1.start ()

    is_read = True
    t2 = threading.Thread (target=mSerial.read_data)
    t2.setDaemon (False)
    t2.start ()

def iprint(msg):
  global callback
  global is_registed

  msg = "[Uart] "+str(msg)
  if is_registed:
    callback.append(msg)
  else:
    print(msg)

def start_sys_cmd():
  global is_registed
  if is_registed:
    t3 = threading.Thread (target=process_receive_sys_cmd)
    t3.setDaemon (False)
    t3.start()

def process_receive_sys_cmd():
  global sys_buff
  global is_registed
  global callback
  #print("process_receive_sys_cmd")
  while is_registed:
    #print ("wait,process_receive_sys_cmd")
    if len(sys_buff):
      #print ("receive,process_receive_sys_cmd")
      line = sys_buff.pop(0)
      if "init" in line:
        if is_opened and is_read and is_write:
          iprint("already open uart")
          break
        iprint("start init")
        init()
    if is_opened:
      break
  iprint("Eixt uart sys thread")

def register_cback(list):
  global callback
  global is_registed

  callback = list
  is_registed = 1


def unregister_cback():
  global callback
  callback.clear()

if __name__ == '__main__':

  receive = []
  register_cback(receive)
  sys_buff.append("init")
  start_sys_cmd()

  def process_receive_msg():
    global receive
    while True:
      #print("wait")
      if len(receive):
        #print("receive")
        print(receive.pop(0))

  t = threading.Thread(target=process_receive_msg)
  t.setDaemon(False)
  t.start()

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