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rin67630
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Joined: Fri Mar 04, 2016 10:15 am

Seeking for the best way to interface with another app over serial.

Sun Mar 24, 2019 9:33 pm

Hi,
I am currently seeking for the best way to interface with another app over serial.

The other app is a blackbox that expects to get every second an incoming byte from a parametrable "serial connection" (e.g. /dev/ttyS0)
At the beginning we get an initial short handshake with a control byte sent from the app which must be responded by a given byte before the (slow) data stream starts.

The pty — Pseudo-terminal utilities looked promising to create a symbolic serial device that could act as a real one.

https://docs.python.org/3/library/pty.html

But it turned out to be tougher than it appeared. The code...

Code: Select all

master,slave = pty.openpty() #open the pseudoterminal
s_name = os.ttyname(slave) #translate the slave fd to a filename

print ("Pseudo serial name is: ")
print (s_name)
ser = Serial(s_name, 9600, timeout=1)
...reveals that the Pseudo-terminal utilities do create a quasi random device which name is /dev/pty/[n], whereas n is variable.
I could not find a way to configure a fixed device name.
Morever the device is always created with restricted rights, so I could not even read the stream with Minicom.

Apparently the library does not allow to change that.

These two unwanted behaviours act for me as a showstopper.
Has someone got either a clue on how to manage predictable and open devices with the pty library, or know another library to get the job done in Python3?

Thank you for your advices...
Laszlo

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