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Topic: IDE 1.8.9 creates multiple COM port entries when re-connecting the board (Read 360 times) previous topic - next topic


I updated to 1.8.9 from 1.8.5, but is now back using the older version.

With the 1.8.9 I sometimes get the relevant COM-port listed more than once and the IDE can't resolve in between them (for example two COM7 both ticked as being the selected one). Upload doesn't work and it seems persistent.

So far I haven't been able to pin-point what situation that might trigger the issue; probably either or both of:
- re-connecting the board
- having to reset the board manually when upload gets stuck (e.g. due to having loaded a non-working sketch...)

Currently using Adafruit Feather M0, should that play a role.



It is entirely feasible that you are seeing two seperate com ports.

The feather is similar to the MKR series and that has two ports.

1. The regular post you would see to initiate an upload and monitor serial traffic.

2. The BOOTLOADER port which is only generally available after upload has started and if you wish then by double clicking the reset quickly to force it into bootloader mode.

3. Very rare but not unknown is for USB 3.0 to cause random swapping of ports for no apparent reason.

4. Laptops using power saving on the USB ports and waking up the board.

You should rule out the power saving and USB 3.0 issues if you can by using a regular computer with power saving OFF and USB 2.0 ports.


It may not be the answer you were looking for but its the one I am giving based on either experience, educated guess, google or the fact that you gave nothing to go with in the first place so I used my wonky crystal ball.


The feather might play a role. But I have seen a few reports on this site which, if I'm not mistaken, show this behaviour for other boards.

You will have to do a search but it might be tricky to find the correct search terms.

You can try the hourly build and see if that solves the issue.
If you understand an example, use it.
If you don't understand an example, don't use it.

Electronics engineer by trade, software engineer by profession. Trying to get back into electronics after 15 years absence.


This is a known bug with Arduino IDE 1.8.9:

It's actually two bugs that are triggered by the same event:
  • Duplicate ports listed in Tools > Port menu.
  • Spurious upload failure.

Both are fixed in the beta build of the Arduino IDE, while only the latter is fixed in the hourly build of the Arduino IDE. Since the hourly build of the Arduino IDE tends to be a bit more stable than the beta build and the duplicate ports listing is only a cosmetic issue, my recommendation is to use the hourly build:


Thanks @pert for reporting this bug with 1.8.9.

I experienced it the other night when using a Feather 32U4 Bluefruit LE.

I was trying to see if  the monitor would stay working on a native USB board when usb power was removed and restarted. It did not, and indeed created the dual port issue.

This testing was in response to this posting about the serial monitor behaviour with the Arduinos with the secondary usb driver chips. https://forum.arduino.cc/index.php?topic=633968.msg4293808#msg4293808


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