[BUG] Marlin fails to boot when enabling UART3 on SKR 1.4

[zeleps]

Bug Description

On an SKR 1.4, when setting either serial port to 3 (UART3), the printer does not start. It appears that the firmware fails to initialize, and it restarts every 2 seconds, failing to reach boot screen. Unfortunately, I have no other means to debug the issue at this point.

Configuration Files

Marlin.zip

Additional Information

Tested in latest bugfix. UART3 pins (4_28 & 4_29) are unused. Tried a lot of different configuration options to no avail. Since the printer does not boot, I have no feedback on what's causing the issue, and I can't think of a way to debug this. Any debugging tips are welcome.

While the intention was to use ESP-01S on the port, the issue remains without the module attached.

[rhapsodyv]

Probably related to: #20783.
@X-Ryl669 can you take a look?

[zeleps]

Interesting, I noticed the templates when looking into my issue, didn't know it was so recent. I'll try to roll back before #20783 and see if the problem persists. Cheers!

[zeleps]

Indeed, I had a branch locally from Jan 9, no issue there. It looks like #20783 still has some bugs...

[X-Ryl669]

Can you enable #20492 code to get a backtrace ?

[GMagician]

I found some reboot causes and fixed with #20938, you may give it a try, maybe can also fix your issue

[zeleps]

@X-Ryl669 it seems the issue was introduced before your code was merged. @GMagician I'm trying to find the exact commit that caused the issue, after that I'll try your solution.

I'll get back to you with conclusions within the next hour.

[zeleps]

Ok, the commit that breaks my configuration is #20810. It's not an obvious issue and it's a bit late to work it out rn, I'll give it a try tomorrow.

[GMagician]

Ok, the commit that breaks my configuration is #20810. It's not an obvious issue and it's a bit late to work it out rn, I'll give it a try tomorrow.

Maybe you should only properly set KILL_PIN_STATE

[zeleps]

I don't have a KILL_PIN.

The problem is that I have DEV_MODE enabled and setup() tries to write debug output to the serial before it's initialized. Moving serial port initialization at the top of the function solved the issue.

@Rockman18 please check if initializing serial ports before kill_pin etc works for you, cause I don't want to break your changes.

[zeleps]

I have created PR #20944 to address the issue, if there's more discussion on this, it should continue there. @Rockman18 please verify that #20944 is not breaking your change.

[Rockman18]

@zeleps : Check ! It's ok for me !

[github-actions]

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