Python Serial Write Timeout
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- Feb 03, 2019 I am learning Python new and i want send to date and time but i have some problem. When i write to input method something, i can send to my message.But the message been date and time on windows,cannot send to arduino.
- Raspberry Pi とか arduino が流行っており 通信することもあるだろうと思うので、 シリアル通信ライブラリ pysserial の使い方を知っておく.
PySerial Documentation, Release 3.4. Python -m serial.tools.listportswill print a list of available ports. It is also possible to add a regexp as first argument and the list will only include entries that matched. writetimeout(float) – Set a write timeout value. Do specify a timeout when opening the serial port otherwise it could block forever if no newline character is received. Also note that readlines only works with a timeout. Readlines depends on having a timeout and interprets that as EOF (end of file). It raises an exception if the port is not opened correctly. Welcome to pySerial’s documentation¶. This module encapsulates the access for the serial port. It provides backends for Python running on Windows, OSX, Linux, BSD (possibly any POSIX compliant system) and IronPython. The module named “serial” automatically selects the appropriate backend.
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Sign upMore than 3 years have passed since last update. PySerialを使ったシリアル通信 未だに組み込み系においては何かとお世話になるシリアル通信。最近ではRaspberry Piなどの組み込みようとに使えるLinuxボードが出てきているので、Pythonから. Raspberry Pi とか arduino が流行っており 通信することもあるだろうと思うので、 シリアル通信ライブラリ pysserial の使い方を知っておく.
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Comments
commented Oct 4, 2015
When I set a timeout like this: pyserial just retries reads like this: I need to be able to know, when the read has timed out to resend my last message. Please raise a TimeoutError, so I can use pyserial like this: I think that it is unpythonic to silently drop errors like a timeout. When a user of pyserial invokes a read(), the expected outcome is that it returns the data that has been read. So hitting the timeout is an error. |
commented Oct 4, 2015
I found a workaround of using threads that communicate over queues: |
commented Oct 4, 2015
You can detect that there was a timeout by checking the length of returned bytes versus the number of bytes requested. It is more like an EOF in Python, rather than a timeout error. That is also how some protocols are using the timeout, as packet delimiter.
An exception would be inconvenient in many cases. E.g. consider reading more than one byte but fewer arrive, the timeout strikes. Then you'd still expect to get the bytes, but how? Attached to the exception? Probably not where most people would expect to find data. When they would be returned with the current |
commented Oct 6, 2015
Thanks for your reply, @zsquareplusc. Checking the length of the returned bytes did not work for me. If I requested a specified number of bytes with a timeout, I would either expect that exact number of bytes or an exception. I am not sure if it would also be OK to return all bytes that have been read up to the timeout. That would definitely need to be documented and users would need to check whether the received data is complete. I think there is little value in aborted data, because the timeout can strike at any given instance, so users would need to program every eventuality. In practice this means to handle as many cases as characters requested. Restarting the communication should be easier to program in most cases. |
I need to communicate with an Arduino. When I use serial.readline() to read what Arduino has to say it works fine. But when I useserial.write('something') doesn't seem to do anything.
Interesting thing is that if I write the same code in the console or command-line, it works as expected..
Python Serial.serialutil.serialtimeoutexception Write Timeout
Using Python 2.7.
Python code:
Arduino code:
Again, Python code runs fine from the console, so no idea why this happens.
1 Answer
Closely related to To know the state of USB (Serial) connection (connected or not connected)
I would not be using Serial.readString() personally. How do you know where the string starts and ends? Just check for three 'A' in a row.
Like this:
Note that this will fail (ie. it will light the LED) if it gets something other than 'A' which would include newlines, etc.
What it does it count the number of times it gets the letter 'A'. If it gets something else it resets the count. If 10 seconds elapse without receiving something, the count resets.