[Solved] Nano Serial Debug Port appears dead/no output?


As a part of my experimentation, I wanted to see what the serial debug port was offering, so I hooked up an Adafruit FTDI Friend Serial/USB adapter and tried to see what the serial debut port was telling me.

The device is in “force boot” mode for programming.

The USB\Serial adapter is set for 3.3v logic levels.

No matter what I tried (swapping USB cables, swapping RX and TX, verifying a good ground, etc.), there was nothing.  I put a 'scope on the serial data lines and ground. . . . and nothing.

Note that this is the first time I messed with these ports.

Is it possible that something I did while flashing the device caused the serial debug port to stop working, or is it just plain 'ole dead?  Is it possible to revert the QSPI to an older version?

When booted into “normal” mode the nano appears to boot correcctly, but the serial debug port is still silent.  Note that I have done nothing to test the GPIO pins yet.

Thanks again for all your help!

Recovery mode will not show anything unless the unit is being flashed. Incidentally, during normal operation, logging or output to that port during boot stages is independent of when Linux is running. For a stage to do this it has to be set up to log there. On a Nano logging enabled is the default, and normal boot should show activity during both boot stages and running Linux.

Serial console is very reliable, and very hard to cause it to fail. If the system can boot normally, then I would find it rare for there to be no serial console output unless it was intentionally set to not log. What you are seeing is normal. Have you examined serial console output while QSPI is being flashed? During that time the “3p server” is running and responding in a much more basic manner than what goes on during normal boot.

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Well I’ll be. . . . . dipped!

Today, this is exactly the behavior I experienced.

Yesterday, I would have sworn in court that I tried it both ways : man_facepalming: and I was getting nothing.

Today it’s working like a charm.

(Whew!  I thought I fried my serial debug port. . .)

Don’t you just hate voodoo magic in electronics? :wink:

Long ago I had a Voodoo 3dfx GPU accelerator…before NVIDIA was on the scene. I found Voodoo magic useful back then. I’m ok with space magic and electronic magic so long as the capacitors are high enough quality to not fail under the load. 😁

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