[BUG] FTMotion: after power loss printing is restarted from very beginning

[vovodroid]

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

Yes, and the problem still exists.

Bug Description

With FT_MOTION enabled printed file is started again from the very beginning. First X/Y homing is performed (as expected), next after full XYZ homing file is printed again.

video_2025-10-07_16-08-11-edit.mp4

Bug Timeline

No response

Expected behavior

Resume printing from the interrupted point.

Actual behavior

Printing is restarted from the very beginning.

Steps to Reproduce

Enable FTMotion, PLR, start print.
Pause print, reset printer, resume printing.

Version of Marlin Firmware

bugfix-2.1.x, 2025-10-07 (commit 0937fe5)

Printer model

Custom

Electronics

BTT SKR-3, TMC2209, sensorless homing, BTT Microprobe

LCD/Controller

No response

Other add-ons

No response

Bed Leveling

ABL Bilinear mesh

Your Slicer

None

Host Software

None

Don't forget to include

• A ZIP file containing your Configuration.h and Configuration_adv.h.

Additional information & file uploads

Marlin.zip

[ellensp]

the default setting save state is only updated when Z position is changed, if your still on the first layer it re-starts at the beginning of that layer

[vovodroid]

It wasn't first layer, may be 3rd-5th. The same test without FTM seems working properly.

I see there are issues and PRs related to Z probing with FTM (including BTT Microbrobe, like my setup). Could it be related?

[narno2202]

I don't think that is related to the microprobe as you disable FT_MOTION for homing and probing. On printer start, all the data related to FT_MOTION are reset. When the PLR stuff is done, FT_MOTION has no information about X, Y, Z, and E positions. We probably need to inject resume_pos in FT_MOTION.

As you have a Biqu Microprobe wired on the Z min stop, could you enable homing and probing with the probe in Configuration_adv.h and enable DELAY_BEFORE_PROBING with the default value and report the results?

[vovodroid]

enable homing and probing with the probe

@narno2202, which options? #define FTM_HOME_AND_PROBE ?

[narno2202]

Yes

[vovodroid]

Well, with

#define FTM_HOME_AND_PROBE
#define DELAY_BEFORE_PROBING 200 

Marline died on homing Z with error "Homing failed. Reset printer" after moving to center without going down.

[narno2202]

Did the probe deploy and is it wired as I think on the Z min endstop ?

[vovodroid]

is it wired as I think on the Z min endstop ?

Yes, according to BTT instruction for SKR 3:

Did the probe deploy

Yes, and went down for a few millimeters.

video_2025-10-08_18-47-25--.mp4

[narno2202]

Ok, many thanks. With FT_MOTION enabled for homing and probing, with a delay this probe works or not depending on the MCU and the wiring, so let's wait for @dbuezas PR (as my configs are working with a delay).

Regarding your issue, perhaps a call to stepper.ftMotion_syncPosition() after the PLR stuff is done would be enough (I don't have PLR so I can't test).

[vovodroid]

perhaps a call to stepper.ftMotion_syncPosition() after the PLR stuff is done would be enough

Unfortunately no. I added (without FTM_HOME_AND_PROBE)

  // Continue to apply PLR when a file is resumed!
  enable(true);

  stepper.ftMotion_syncPosition();

  // Resume the SD file from the last position
  PROCESS_SUBCOMMANDS_NOW(MString<MAX_CMD_SIZE>(F("M23 "), info.sd_filename));
  PROCESS_SUBCOMMANDS_NOW(TS(F("M24S"), resume_sdpos, 'T', info.print_job_elapsed));

but nothing changed - it still goes to the second homing.

[vovodroid]

I don't have PLR so I can't test

Actually real PLR (with UPS) isn't needed for testing. Just build it as if it were here, pause print via menu and press reset button.

[narno2202]

In FT_MOTION when a block is loaded, its start position is the end of the previous block. But with PLR we don't have a previous block, only the last saved position on the SD card. On printer restart, ftMotion_init(), reset data. The solution is perhaps to inject the correct position for the previous block: resume_pos. I was ready to test but my power supply just died.
You will find below the 2 modified files if you want to test.

plr_ftmotion.zip

[vovodroid]

Something very impressive))) After XY homing it rushed to maximum XY with terrible sound until head crashed into gantry stop.

video_2025-10-09_20-20-04---.mp4