[英]How to read serial data with multiprocessing in python?
I have a device that outputs data at irregular intervals. 我有一台以不规则间隔输出数据的设备。 I want to write data onto a csv in 2 second intervals.
我想每隔2秒将数据写入CSV。 So I figured multiprocessing with a queue might work.
因此,我认为使用队列进行多重处理可能有效。
Here I'm trying to just pass data from one process to another but I get Serial Exception. 在这里,我试图将数据从一个进程传递到另一个进程,但出现串行异常。 Also, I'm unable to run it on IDLE.
另外,我无法在IDLE上运行它。 So I'm stuck with using the terminal.
所以我坚持使用终端。 As a result, the error message closes as soon as it opens.
结果,错误消息一打开就关闭。
Here's the code: 这是代码:
import multiprocessing
import time
import datetime
import serial
try:
fio2_ser = serial.Serial("COM3",
baudrate=2400,
bytesize=serial.EIGHTBITS,
parity =serial.PARITY_ODD)
except serial.SerialException:
print("FiO2 Analyser Device not detected")
def Read_Data(q):
global fio2_ser
while True:
try:
fio2_data = fio2_ser.readline().decode('utf-8')
fio2_data = str(fio2_data).replace("\r\n","")
fio2_data = fio2_data.replace("\x000","")
except:
fio2_data = "FiO2 Data Unavailable"
q.put(fio2_data)
def Disp_Data(q):
while q.empty() is False:
fio2_data = q.get()
print(fio2_data)
time.sleep(2)
if __name__ == "__main__":
q = multiprocessing.Queue()
p1 = multiprocessing.Process(target=Read_Data, args=(q,))
p2 = multiprocessing.Process(target=Disp_Data, args=(q,))
p1.start()
p2.start()
p1.join()
p2.join()
When I run a separate module to collect data, it runs fine and collects data. 当我运行一个单独的模块来收集数据时,它可以正常运行并收集数据。
import serial
try:
fio2_ser = serial.Serial("COM3",
baudrate=2400,
bytesize=serial.EIGHTBITS,
parity =serial.PARITY_ODD)
except serial.SerialException:
print("FiO2 Analyser Device not detected")
def Reader():
global fio2_ser
try:
fio2_data = fio2_ser.readline().decode('utf-8')
fio2_data = str(fio2_data).replace("\r\n","")
fio2_data = fio2_data.replace("\x000","")
return fio2_data
except:
return "FiO2 Data Unavailable"
if __name__ =='__main__':
value = Reader()
print(value)
The Disp_Data() function will stop running when q.empty() is True. 当q.empty()为True时,Disp_Data()函数将停止运行。 In my case the loop exits immediately.
就我而言,循环立即退出。
Might be useful to display the error message thrown by SerialException to see the cause: 显示由SerialException抛出的错误消息以查看原因可能很有用:
except serial.SerialException as msg:
print( "Error opening serial port %s" % msg)
Also, it would be better to gracefully shut down the child-processes. 同样,最好适当地关闭子进程。 In my case, they kept running after killing the main process, so the Read_Data() process keeps the port open.
就我而言,它们在终止主进程后仍保持运行,因此Read_Data()进程使端口保持打开状态。
The multiprocessing module doesn't like pickling pyserial. 多处理模块不喜欢腌制pyserial。
This following code snip works on my Windows10 box 以下代码片段可在我的Windows10机器上使用
import threading, multiprocessing
import time
import serial
import sys
def OpenSerialPort(port=""):
print ("Open port %s" % port)
fio2_ser = None
try:
fio2_ser = serial.Serial(port,
baudrate=2400,
bytesize=serial.EIGHTBITS,
parity =serial.PARITY_ODD)
except serial.SerialException as msg:
print( "Error opening serial port %s" % msg)
except:
exctype, errorMsg = sys.exc_info()[:2]
print ("%s %s" % (errorMsg, exctype))
return fio2_ser
def Read_Data(queue, serialPort, stopped):
print ("Start reading data.")
serialPort.timeout = 1.0
while not stopped.is_set():
fio2_data = ''
try:
#print "Reading port..."
fio2_data = serialPort.readline()
except:
exctype, errorMsg = sys.exc_info()[:2]
print ("Error reading port - %s" % errorMsg)
stopped.set()
break
if len(fio2_data) > 0:
fio2_data = fio2_data.decode('utf-8')
fio2_data = str(fio2_data).replace("\r\n","")
fio2_data = fio2_data.replace("\x000","")
queue.put(fio2_data)
else:
queue.put("Read_Data() no Data")
serialPort.close()
print ("Read_Data finished.")
def Disp_Data(queue, stopped):
print ("Disp_Data started")
while not stopped.is_set():
#print "Check message queue."
if queue.empty() == False:
fio2_data = queue.get()
print(fio2_data)
print ("Disp_Data finished")
if __name__ == "__main__":
#serialPort = OpenSerialPort('/dev/ttyUSB0')
serialPort = OpenSerialPort('COM3')
if serialPort == None: sys.exit(1)
queue = multiprocessing.Queue()
stopped = threading.Event()
p1 = threading.Thread(target=Read_Data, args=(queue, serialPort, stopped,))
p2 = threading.Thread(target=Disp_Data, args=(queue, stopped,))
p1.start()
p2.start()
loopcnt = 20
while (loopcnt > 0) and (not stopped.is_set()):
loopcnt -= 1
print ("main() %d" % loopcnt)
try:
time.sleep(1)
except KeyboardInterrupt: #Capture Ctrl-C
print ("Captured Ctrl-C")
loopcnt=0
stopped.set()
stopped.set()
loopcnt=0
print ("Stopped")
p1.join()
p2.join()
serialPort.close()
print ("Done")
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