Serial Monitor stops printing output

[galinawind]

Describe the problem

The serial monitor output works for anything in the setup() subroutine. The serial monitor stops working for anything in loop().

This problem started after I upgraded from Ubuntu 18.04 to Ubuntu 20.04 LTS.

I am doing a complicated operation set using a NeoKey 1x4 and I need to see that the buttons are registering callbacks correctly. I would start the program. If I immediately hit one of the keys, it would output for some time. If I pause for even a tiny bit, the serial monitor freezes. If I navigate to a web browser or something, the serial monitor freezes. I can un-freeze it temporarily by randomly changing the baud rate from the drop-down menu. Any change at all, to anything at all, unfreezes the monitor, but again, only temporarily.

To reproduce

1. Connect Adafruit Feather RP2040 and NeoKey 1x4 with a StemmaQT cable.
2. Plug the lot into the USB port.
3. Upload the basic_callback sketch to the Adafruit Feather RP2040 board.
4. Push the buttons on the NeoKey 1x4 a couple of times so that you see the printouts.
5. Navigate away from the IDE to a web browser, or any other window.
6. Come back to the IDE
   🐛 Nothing is being printed anymore.
7. Change the baud rate from the drop-down menu on the serial monitor.
   You will see that the printouts are appearing again.
8. Stop interacting for like a count of 5.
   🐛 The serial monitor will freeze again.

Expected behavior

Serial Monitor does not freeze.

Arduino IDE version

2.3.2 and 2.3.4

Operating system

Linux

Operating system version

Ubuntu 20.04 LTS

Additional context

Discussion: https://forum.arduino.cc/t/arduino-ide-and-ubuntu-20-04-serial-monitor-problems/1345265

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The fault does not occur when I use Serial Monitor on my Intel MacBook Pro.

Issue checklist

• I searched for previous reports in the issue tracker
• I verified the problem still occurs when using the latest nightly build
• My report contains all necessary details

[per1234]

Thanks for your report @galinawind. Please tell us whether the fault still occurs if you upload this simple sketch to the board:

void setup() {
  Serial.begin(9600);
}

void loop() {
  Serial.println("hello");
  delay(1000);
}

[galinawind]

There is no fault if this simple sketch runs. To be exact, there is never any fault. There is never any error anywhere. The Serial monitor just stops working.

[per1234]

there is never any fault. There is never any error anywhere. The Serial monitor just stops working.

When I said "fault", I was referring to the problem you are reporting:

the serial monitor freezes

Now please provide the information I requested in my previous comment: After you upload the simplified sketch to your board, does the Serial Monitor freeze on your Linux computer like it does when the board is running the complex "basic_callback" sketch?

[galinawind]

No, the serial monitor does not freeze when I run a simple sketch.

I now have a work-around. Everything works perfectly if I use the Mac build of the 2.3.4 IDE. I don't like Macs and my Intel MacBook Pro is a piece of trash, but this one thing works on it. Hopefully you can fix the Linux build at some point.