[BUG] mmu2 does not reset with SW Reset

[ChGeorgi]

Did you test the latest bugfix-2.1.x code?

Yes, and the problem still exists.

Bug Description

Marlin sends during boot ?X0 instead of X0 i fixed it by sending a "start" before X0 (but can also only be a blank)

Bug Timeline

No response

Expected behavior

reset of mmu2

Actual behavior

mmu2 will be disabled

Steps to Reproduce

connect mmu2 without reset cable

Version of Marlin Firmware

2.0.9.2

Printer model

self designed almost like prusa mk3s

Electronics

skr 1.4 /skr 2.0

Add-ons

MMU2S with clone board

Bed Leveling

ABL Bilinear mesh

Your Slicer

Prusa Slicer

Host Software

SD Card (headless)

Don't forget to include

• [X] A ZIP file containing your Configuration.h and Configuration_adv.h.

Additional information & file uploads

nothing else

[thinkyhead]

The code is only sending "X0" so it's not clear where the "?" is coming from on your serial line.

  MMU2_SERIAL.begin(MMU_BAUD);
  safe_delay(10);
  MMU2_COMMAND("X0"); // Send soft reset

You can try experimenting with a longer safe_delay, or you might try adding MMU2_SERIAL.flushTX(); to see if it makes a difference in the reliability of startup.

[ChGeorgi]

The '?' appears directly at startup. Followed by the X0 later. So Its something before.

[GMagician]

May this be caused by noise on usart line? You don't send anything but noise causes bits to be loaded into shift register.