Uno waiting for serial answer after Serial.write?

Using Arduino Networking, Protocols, and Devices
1

On my notebook I have a USB port that is powered even if the computer is turned off. In my sketch I measure battery voltage every few seconds and send the value via Serial.writeln to the computer and after a few minutes I save a summary to the EEPROM (the power is lost for a short moment when powering on the computer but long enough to reset Arduino even with my largest cap between GND and 5V).
When I turn the computer off the Arduino works but when it should send data the TX LED stays on instead of a short blink. I am not sure what happens and din't test it because I din't want to turn computer on, make a test, turn it off, turn it on and see results, repeat...
I have used this method with another sketch on Arduino Nano clone with the CH 340 USB/serial converter and it worked well. When uploading the sketch on the Nano works as expected. Do you have any ideas where may be a problem? Does the stuck TX mean the whole Arduino is stuck?
Thanks for help.

2

Smajdalf:
Does the stuck TX mean the whole Arduino is stuck?

I don't know but it would be very easy to add some test code. Just make another LED bink. If it continues to do so the answer is NO.

...R

3

Well I hoped it is a know "feature". Because discovering if the Arduino is stuck is just a minor (and easy) part of the problem. There are many more questions: why this happens? What else is not working as expected when this happens? What will the Serial do when the computer starts responding again? Ofc I could get answers myself by experimenting and possibly reading the source codes of Serial library and the USB/Serial converter but I hoped someone else encountered such behavior because it doesn't look like so rare to send data to USB without an active Master on the other side.

4

send the value via Serial.writeln

No such method.

5

PaulS:
No such method.

Sorry, meant Serial.println

6

I KNOW that an Arduino will happily Serial.print() for ever when nothing is connected to the Serial port. AFAIK my PC switches off its USB ports when it shuts down so I have never thought to try what you are describing.

Why don't you do the testing and become the Forum expert on the subject.

...R