Serial Monitor should handle disconnects more gracefully

[cinderblock]

Edit from maintainers - Temporary solution: https://docs.platformio.org/en/latest/faq/advanced-serial-monitor.html

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Serial Monitor should handle disconnects more gracefully

This is a bug report/feature request to improve the serial port functionality in Platform IO.

Configuration

Operating system: Windows 10 x64

PlatformIO Version (platformio --version): PlatformIO Core, version 5.1.1

Description of problem

Using serial monitor on a USB based serial port crashes with Exception

Steps to Reproduce

1. Start a serial monitor to a device with a USB based serial port: pio device monitor
2. Reset the device

Actual Results

Exception in thread rx:
Traceback (most recent call last):
  File "C:\Users\camer\.platformio\python3\lib\threading.py", line 926, in _bootstrap_inner
    self.run()
  File "C:\Users\camer\.platformio\python3\lib\threading.py", line 870, in run
    self._target(*self._args, **self._kwargs)
  File "c:\users\camer\.platformio\penv\lib\site-packages\serial\tools\miniterm.py", line 445, in reader
    data = self.serial.read(self.serial.in_waiting or 1)
  File "c:\users\camer\.platformio\penv\lib\site-packages\serial\serialwin32.py", line 257, in in_waiting
    raise SerialException("ClearCommError failed ({!r})".format(ctypes.WinError()))
serial.serialutil.SerialException: ClearCommError failed (PermissionError(13, 'The device does not recognize the command.', None, 22))

Expected Results

An error message designed for a novice user to understand.

Ideally also (optional) automatic reconnect when the device comes back.

[jcw]

For references, here is the slightly different traceback on MacOS:

--- exit ---
Traceback (most recent call last):
  File "/usr/local/Cellar/platformio/5.2.5/libexec/lib/python3.9/site-packages/serial/serialposix.py", line 575, in read
    buf = os.read(self.fd, size - len(read))
OSError: [Errno 6] Device not configured

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/local/Cellar/python@3.9/3.9.12/Frameworks/Python.framework/Versions/3.9/lib/python3.9/threading.py", line 973, in _bootstrap_inner
    self.run()
  File "/usr/local/Cellar/python@3.9/3.9.12/Frameworks/Python.framework/Versions/3.9/lib/python3.9/threading.py", line 910, in run
    self._target(*self._args, **self._kwargs)
  File "/usr/local/Cellar/platformio/5.2.5/libexec/lib/python3.9/site-packages/serial/tools/miniterm.py", line 499, in reader
    data = self.serial.read(self.serial.in_waiting or 1)
  File "/usr/local/Cellar/platformio/5.2.5/libexec/lib/python3.9/site-packages/serial/serialposix.py", line 581, in read
    raise SerialException('read failed: {}'.format(e))
serial.serialutil.SerialException: read failed: [Errno 6] Device not configured

[belm0]

This is a basic thing (e.g. done by the Arduino IDE monitor), so I'd like to see it.

Most UI's would use some connection status indicator (Arduino IDE uses backgroud color), but for a simple text terminal it should be enough to print <disconnect>.

Maybe this is complicated by device / port autodetection by device monitor, but a first pass would have it only reconnect to the same port.

[belm0]

pyserial itself doesn't have any special reconnect support: pyserial/pyserial#558

if monitor implements this, it will have to be in a crude way like suppress the exception and silently retry connection every second

[belm0]

monitor is using the "miniterm" tool of pyserial. It's basically a stand-alone program, and exceptions happen in background threads. So it will be hard to control error output.

options for implementing reconnect:

1. live with the spamming on the output when there are disconnects, and during retry polling
2. try to filter stderr to suppress the spam
3. fork miniterm (about 1,000 loc) and enhance it for reconnect
4. contribute reconnect option to miniterm and use it <--

[belm0]

I implemented --reconnect option for pyserial miniterm... but then realized this project appears unmaintained (no commits in 6 months, backlog of PR's) 😢

pyserial/pyserial#651

[ivankravets]

@belm0, thank you so much for your contribution to the OSS.

How about having a separate PR that just catches exceptions or exits gracefully without reconnecting? Typically, this issue arises when a user does not close the serial terminal but unplugs the board.