Pyserial Write() Instant Timeout

EDIT I found out what the problem was and have answered my own question. Original question below this line I have a serial bridge between COM4 and COM5 implemented in software (Spe

Solution 1:

The clue is in the error message[1]

File "C:\Python27\lib\site-packages\serial\serialwin32.py", line 270, inwrite
raise writeTimeoutError

so we open that file and find:

if self._writeTimeout != 0: # if blocking (None) or w/ write timeout (>0)# Wait for the write to complete.#~ win32.WaitForSingleObject(self._overlappedWrite.hEvent, win32.INFINITE)
            err = win32.GetOverlappedResult(self.hComPort, self._overlappedWrite, ctypes.byref(n), True)
            if n.value != len(data):
                raise writeTimeoutError

Read that first conditional again:

ifself._writeTimeout!=0:

so let us rewrite our code from before

send = serial.Serial(port = 'COM4', baudrate = 9600, timeout = 0)

becomes

send = serial.Serial(port = 'COM4', baudrate = 9600, writeTimeout = 0)

and Et Voila: No exception.

[1] Well Designed Error Messages? That's new!

Solution 2:

The problem may be that the interface tries to comply with RTS, CTS, DSR, or DTS signals. It is possible that if they are not properly virtually connected, they can mysteriously affect communication through a timeout.

I would also recommend looking at the configuration of the used virtual serial bridge.

One solution may be to ignore influence using rtscts=False and/or dsrdtr=False when opening the serial port in Python.

I could use an alternative solution for sniffing communication using hub4com, where I used the parameter --octs = off, for example in this way, but the virtual ports had to be created correctly before. hub4com --baud=115200 --route=0:All --route=1:All --route=2:All --no-default-fc-route=All:All --octs=off \\.\COM1 \\.\CNCB0 \\.\CNCB1