Issue with python serial: ValueError: Attempting to use a port that is not open

Question

我正在尝试使用树莓派 pi3 中的 python 从血压计获取数据。我用谷歌搜索并找到了一些使用 python.

获取数据的示例

我的代码：

#!/usr/bin/python
import serial
neo = serial.Serial(
    port='/dev/ttyUSB0',
    baudrate=9600,
    parity=serial.PARITY_NONE,
    stopbits=serial.STOPBITS_ONE,
    bytesize=serial.EIGHTBITS,
    timeout=0
)
print("connected to: " + neo.portstr)

#neo.open()      #opens port
print "Is port open ? ",neo.isOpen()    #returns true?

#ser.write("help\n");
while True:
    dataline = neo.readline();
    if dataline:
        print(dataline), neo.close()

当我运行上面的代码使用“sudo python pyusb.py”命令时，它返回以下错误：

connected to: /dev/ttyUSB0
Is port open ?  True
None
Traceback (most recent call last):
  File "pyusb.py", line 18, in <module>
    dataline = neo.readline();
  File "/usr/lib/python2.7/dist-packages/serial/serialposix.py", line 443, in read
    if not self._isOpen: raise portNotOpenError
ValueError: Attempting to use a port that is not open

如果取消注释行“neo.open()”，则会抛出另一个错误：

connected to: /dev/ttyUSB0
Traceback (most recent call last):
  File "pyusb.py", line 13, in <module>
    neo.open()      #opens port
  File "/usr/lib/python2.7/dist-packages/serial/serialposix.py", line 271, in open
    raise SerialException("Port is already open.")
serial.serialutil.SerialException: Port is already open.

我看过类似的问题。但是覆盖“serial.Serial()”方法存在问题。我无法确定上面的代码到底出了什么问题。任何人都可以帮助我，我在那里做错了什么？

Answer 1

如果您查看 pyserial 的文档，http://pyserial.readthedocs.io/en/latest/shortintro.html#readline 它说您必须在使用 readline() 时指定超时。这是因为 readline() 在每次传输结束时等待 EOL 字符。尝试使用如下方法将超时增加到 1：

import serial
neo = serial.Serial(
    port='/dev/ttyUSB0',
    baudrate=9600,
    parity=serial.PARITY_NONE,
    stopbits=serial.STOPBITS_ONE,
    bytesize=serial.EIGHTBITS,
    timeout=1
)
print("connected to: " + neo.portstr)

while True:
    dataline = neo.readline();
    print dataline

Issue with python serial: ValueError: Attempting to use a port that is not open

Issue with python serial: ValueError: Attempting to use a port that is not open

python

pyserial

uart

raspberry-pi3