1. Python Check If Serial Port Is Available In Florida
2. Parallel Port
3. Python If Serial Available

A port cannot be opened in exclusive access mode if it is already open in. An instance of bytes when available (Python 2.6 and newer) and str otherwise. I've got a Python program which is reading data from a serial port via the PySerial module. The two conditions I need to keep in mind are: I don't know how much data will arrive, and I don't know when to expect data. How can I know if a certain port is open/closed on linux ubuntu, not a remote system, using python? How can I list these open ports in python? Netstat: Is there a way to integrate netstat output.

I am using a script in Python to collect data from a PIC microcontroller via serial port at 2Mbps.

The PIC works with perfect timing at 2Mbps, also the FTDI usb-serial port works great at 2Mbps (both verified with oscilloscope)

Im sending messages (size of about 15 chars) about 100-150x times a second and the number there increments (to check if i have messages being lost and so on)

On my laptop I have Xubuntu running as virtual machine, I can read the serial port via Putty and via my script (python 2.7 and pySerial)

The problem:

• When opening the serial port via Putty I see all messages (the counter in the message increments 1 by 1). Perfect!
• When opening the serial port via pySerial I see all messages but instead of receiving 100-150x per second i receive them at about 5 per second (still the message increments 1 by 1) but they are probably stored in some buffer as when I power off the PIC, i can go to the kitchen and come back and im still receiving messages.

Here is the code (I omitted most part of the code, but the loop is the same):

Anyone knows why pySerial takes so much time to read from the serial port till the end of the line?Any help?

I want to have this in real time.

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Thank you

Vasco BaptistaVasco Baptista

4 Answers

You can use inWaiting() to get the amount of bytes available at the input queue.

Python Check If Serial Port Is Available In Florida

Then you can use read() to read the bytes, something like that:

Why not to use readline()at this case from Docs:

You are waiting for the timeout at each reading since it waits for eol. the serial input Q remains the same it just a lot of time to get to the 'end' of the buffer, To understand it better: you are writing to the input Q like a race car, and reading like an old car :)

Kobi KKobi K

You need to set the timeout to 'None' when you open the serial port:

This is a blocking command, so you are waiting until you receive data that has newline (n or rn) at the end:line = ser.readline()

Once you have the data, it will return ASAP.

From the manual:

Possible values for the parameter timeout: … x set timeout to x seconds

and

readlines(sizehint=None, eol='n') Read a list of lines, until timeout. sizehint is ignored and only present for API compatibility with built-in File objects.

Parallel Port

Note that this function only returns on a timeout.

So your readlines will return at most every 2 seconds. Use read() as Tim suggested.

Python If Serial Available

mswmsw

A very good solution to this can be found here:

Here's a class that serves as a wrapper to a pyserial object. It allows you to read lines without 100% CPU. It does not contain any timeout logic. If a timeout occurs, self.s.read(i) returns an empty string and you might want to throw an exception to indicate the timeout.

It is also supposed to be fast according to the author:

The code below gives me 790 kB/sec while replacing the code with pyserial's readline method gives me just 170kB/sec.

JoeJoe

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