Intermittent comm port connection depending on serial monitor

Official Hardware UNO Family UNO R4 WiFi
1

Just got the r4 and updated thefirmware to the latest version 0.4.1 .
I try to upload a sketch and I get an error,

Cannot perform port reset: TOUCH: error during reset: opening port at 1200bps: Serial port busy
No device found on COM3.
"C:\Users\zleep\AppData\Local\Arduino15\packages\arduino\tools\bossac\1.9.1-arduino5/bossac" -d --port=COM3 -U -e -w "C:\Users\zleep\AppData\Local\Temp\arduino\sketches\44C57B0641BDF2EF74BECF72C0908594/Blink.ino.bin" -R
Failed uploading: uploading error: exit status 1

It was connected to comm port but has dropped for some reason.
If I turn on the serial monitor it seems to force it to reconnect to the comm port then I can upload. I have had to retry this a couple of times to get it to work. seems the comm port connection is being dropped for some reason. The IDE does say it is connected before I try to upload the sketch.

2

I've moved your topic to the dedicated Arduino WiFi R4 section of the forum.

3

Hi @ArduinoFan12.

What do you mean by "has dropped"?

This part of the output is expected:

This is only a side effect of the real problem:

The sequence that occurs when uploading to the UNO R4 WiFi:

  1. Arduino IDE sends a special "touch" signal to the serial port of the UNO R4 WiFi.
  2. The UNO R4 WiFi goes into a boot mode.
  3. Arduino IDE runs the bossac command that flashes the sketch binary to the UNO R4 WiFi.

Step (1) in the sequence failed because some other process already had the UNO R4 WiFi's serial port open (as indicated by the "Serial port busy" part of the output). Since the first step failed, the board was never put into the boot mode at step (2). Since the board was not in boot mode, step (3) could not be successful, which is what produced the "No device found on COM3." error.

So the question is: why was the serial port busy at step (1)? Normally we would guess that some external process had opened the port. However, that doesn't match with this observation:

If some external process had the port open, then opening Serial Monitor should also fail. This makes it seem like it is Serial Monitor itself that is interfering with the upload. Serial Monitor is designed to close the port at the start of an upload, and then only open it again after the upload finishes so that it does not cause such interference so this is quite unexpected.

Are you still experiencing this problem? If so, which version of Arduino IDE are you using (e.g., "2.0.1")? The version is shown on the window title bar and also in the dialog that opens when you select Help > About from the Arduino IDE menus.

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