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Power Loss Shutdown and Power Loss Resume

Notice

1. Feature Concepts and Workflow

  • Power Loss Shutdown

    • Concept: Upon detecting an abnormal power loss, the system does not save the current print state and directly performs a safe shutdown.
    • Recovery Workflow: After power is restored, the device will automatically restart and enter standby mode. The previous print job has been aborted, and you will need to manually start a new print.

  • Power Loss Resume

    • Concept: Upon detecting an abnormal power loss, the system will immediately save the current print progress (such as position, layer height), and then shut down.
    • Recovery Workflow: After power is restored, typically requiring user confirmation, the device can resume the unfinished print from the point of power loss.

2. Core Rules

  • Power Loss Shutdown and Power Loss Resume are mutually exclusive features and cannot be enabled simultaneously.
  • If the Power Loss Shutdown feature is enabled, the Power Loss Resume feature will automatically become inactive.

3. How to Choose

  • Choose "Power Loss Shutdown": If you prioritize electrical safety, or prefer the device to automatically start and enter standby mode after power is restored without needing to resume an interrupted print, enable this feature.
  • Choose "Power Loss Resume": If you frequently run long-duration print jobs that cannot afford failure, and wish to resume printing from the interruption point after a power loss, enable this feature.

Wiring​

Power Operation

Before starting, completely turn off the printer and disconnect the power supply. Do not plug or unplug wiring harnesses, organize interface cable sequences, or touch terminals while the system is powered on.

KPPM Wiring Requirements
  • The following instructions apply to the Power Loss Shutdown and Power Loss Resume functions of the FLY-Pi.
  • When connecting other devices via USB, a finished USB power isolator or a finished USB cable containing only data lines must be used to prevent backfeeding 5V power between the two ends. Do not cut or modify cables yourself.
  • Power must be supplied using the dedicated KPPM module. Do not use other power supply methods.
  • If the 5V connection between the host and client board cannot be disconnected, the mainboard must be fully powered off before restarting; otherwise, it may fail to boot properly.
  • FLY-Pi 5V Wiring
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Configuration​

Disable Power-Off Shutdown​

Notice
  • Before using print resume after power loss, ensure that Klipper has started properly and can control the printer.
  • The power-off shutdown feature must be disabled; otherwise, print resume after power loss will not take effect.
  • After disabling power-off shutdown, the device will remain powered. Please ensure that the host machine does not have any other independent power supply connected; otherwise, the device will still not be able to shut down after a power outage.

  • Enter the device's IP address in the browser's address bar, for example: http://192.168.6.179

  • Enter the configuration page

    • Open the device's IP address in the browser, for example: http://192.168.1.2/
    • In fluidd, as shown in the left image below: Uncheck -> Filter hidden files and folders.
    • In mainsail, as shown in the right image below: Check -> Show hidden files.
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    • At this point, you can see the .flyos-config folder. Enter this folder and you will find the sys-config.conf file.
    • The sys-config.conf file is a symbolic link to the config.txt configuration file in the removable disk FlyOS-Conf.
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    • Open the sys-config.conf file and locate the two configurations: shutdown_pin_state and shutdown_pin=.
    • Add # at the beginning of these two configurations.
    • Then Save -> Close, and restart the device.
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plr.cfg Configuration File​

  • In the printer configuration page, locate the plr.cfg file.
  • Clear all existing content, then paste the configuration below.
  • The configuration file content is as follows:
  • The power_pin must use the host GPIO or a pin recommended by the product, and cannot use a pin from the slave (MCU/toolboard).
[mcu host]   
serial: /tmp/klipper_host_mcu

[power_loss_resume]
power_pin: host:gpiochip1/gpio21
is_shutdown: True # Whether to execute shutdown operation, enabled by default
paused_recover_z: -2.0 # If paused during shutdown, Z movement distance when resuming print, default no movement
start_gcode:
    # Gcode to execute before starting resume printing
    # All parameters saved before power loss can be accessed via {PLR}
    # Use M118 {PLR} to output all available parameters
    # M118 {PLR}
    M118 Starting resume printing: {PLR.print_stats.filename}
    M118 Interrupted position: X:[{PLR.POS_X}] Y:[{PLR.POS_Y}] Z:[{PLR.POS_Z}] E:[{PLR.POS_E}]
    # Restore all heater temperatures
    {% for name, heater in PLR.heaters.items() %}
        {% if heater.target > 0 %}
            M118 Setting heater[{heater.name}] target temperature: {heater.target}
            SET_HEATER_TEMPERATURE HEATER="{heater.name}" TARGET={heater.target}
        {% endif %}
    {% endfor %}
    # Wait for extruder temperature
    {% if PLR.toolhead.extruder in PLR.heaters and PLR.heaters[PLR.toolhead.extruder].target > 0 %}
        {% set extruder = PLR.heaters[PLR.toolhead.extruder] %}
        M118 Waiting for [{extruder.name}] to reach target temperature: {extruder.target}
        TEMPERATURE_WAIT SENSOR="{extruder.name}" MINIMUM={extruder.target-5} MAXIMUM={extruder.target+5}
    {% endif %}
    M83                             ; Relative extrusion
    G1 E-2 F1000                    ; Retract
    G91                             ; Relative coordinates
    G1 Z2 F100                      ; Lift Z, prepare for X,Y homing
    G90                             ; Absolute coordinates
    G28 X Y                         ; Home X Y
resume_gcode:
    # Gcode to execute after moving to target position, before starting formal printing
    M83                             ; Relative extrusion
    G1 E4 F800                      ; Extrude 4mm filament, compensate for oozing
layer_count: 2 # Execute layer_change_gcode after printing specified layers during resume
layer_change_gcode:                
    # Gcode to execute after {layer_count} layers of resume printing
    M118 Restoring print speed
    M106 S{PLR.fan_speed}             ; Turn on part cooling fan
    M220 S{PLR.move_speed_percent}    ; Set requested speed percentage
    M221 S{PLR.extrude_speed_percent} ; Set requested extrusion speed percentage
shutdown_gcode:
    # Gcode to execute before shutdown
    M118 Power voltage low, shutting down
    # M112 ; Emergency stop

  • After saving the configuration file above

  • Open the printer.cfg file, and add the following at the very beginning:


    [include plr.cfg]

  • Click "Save & Restart" in the top right corner.

  • This completes the configuration of the Klipper power loss resume function.

About [homing_override]​

Note
  • If [homing_override] is used, do not arbitrarily set the homing position within [homing_override]. Failure to do so may result in print resume failure and no responsibility will be accepted.
  • Configuration instructions for [homing_override] are provided below.
  • Explanation
    • [force_move]: Enables the forced move function, allowing forced movement to a specified position when not homed.
    • [force_move] replaces the set_position_z function in [homing_override]. Failure to configure this way may lead to print resume failure.
    • The [homing_override] configuration below is intended to correctly home the Z-axis during print resume.
[force_move]
enable_force_move: true


[homing_override]
axes: z
gcode:
    {% set max_x = printer.configfile.config["stepper_x"]["position_max"]|float %}
    {% set max_y = printer.configfile.config["stepper_y"]["position_max"]|float %}
    {% if 'z' not in printer.toolhead.homed_axes %}
        SET_KINEMATIC_POSITION Z=0
        G90
        G0 Z5 F600
    {% endif %}
    {% set home_all = 'X' not in params and 'Y' not in params and 'Z' not in params %}

    {% if home_all or 'X' in params %}
    G28 X
    {% endif %}

    {% if home_all or 'Y' in params %}
    G28 Y
    {% endif %}

    {% if home_all or 'Z' in params %}
    G0 X{max_x / 2} Y{max_y / 2}  F3600
    G28 Z
    G1 Z10 F2000
    {% endif %}

  • About Lift Explanation
    • This configuration only executes when the Z-axis is not homed and does not affect normal usage. 
      {% if 'z' not in printer.toolhead.homed_axes %}
          SET_KINEMATIC_POSITION Z=0
          G90
          G0 Z5 F600
      {% endif %}

About Configuration for [gcode_macro _CLIENT_VARIABLE]​

  • When your configuration includes the [gcode_macro _CLIENT_VARIABLE] macro and sets the following variables:
  • Reference
[gcode_macro _CLIENT_VARIABLE]
variable_use_custom_pos: True    # Enable custom position
variable_custom_park_dz: 5       # Set custom park height offset
  • You must accordingly adjust the paused_recover_z parameter in the [power_loss_resume] module, making it opposite in sign to the offset value above.

Configuration Correspondence​

Macro VariablePause/Resume Module ParameterCorrespondence
variable_custom_park_dz: 5paused_recover_z: -5Opposite sign, same value
variable_custom_park_dz: -3paused_recover_z: 3Opposite sign, same value

Example Configuration​

[gcode_macro _CLIENT_VARIABLE]
variable_use_custom_pos: True
variable_custom_park_dz: 5

[power_loss_resume]
paused_recover_z: -5

Important: Failure to maintain this correspondence may lead to incorrect Z-axis height calculation during print resume or pause recovery, affecting the print.

Testing​

First Step Test: Simulating Power Loss via Emergency Stop​

  1. Start printing any file. During the print, click the Emergency Stop button to simulate a power loss scenario.
  2. Click Firmware Restart again and wait for Klipper to reconnect and return to normal.
  3. Check if a popup notification appears on the web interface. If it appears, the print resume function is working correctly.
  4. Subsequently, you can further test with an actual power loss to verify the function's reliability.

Second Step Test: Actual Power Loss Simulation and Function Verification​

  1. Test Preparation: After the system starts normally and connects to Klipper, first confirm the status of the indicator light next to the host computer. Usually, an LED will blink when the system is running. This indicator light is the key one to observe in subsequent steps.
  2. While the device is running normally and connected to Klipper, directly disconnect the power to simulate a real power loss scenario.
  3. Immediately check if the indicator light next to the host computer turns off completely within 5 seconds.
    • If it turns off: The power-off shutdown function is normal. Please proceed with the subsequent steps.
    • If it does not turn off: The automatic shutdown function is not working. This is usually due to incorrect related configurations (such as kppm wiring or settings), which need to be carefully checked and troubleshot.
  4. Wait at least 5 seconds, then reconnect the power. Observe if Klipper automatically reconnects and returns to normal operation. (Saving data and shutting down takes 3-5 seconds).
  5. Check the web interface
    • If a popup notification appears: The print resume function has been successfully activated and is operating normally.
    • If there is no notification: The print resume function did not start as expected. Please systematically check the relevant configurations based on the above observations.
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