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Power Loss Shutdown and Power Loss Recovery

Important Notes

1. Function Concepts and Processes

  • Power Loss Shutdown

    • Concept: When an abnormal power loss is detected, the system does not save the current printing state and directly executes a safe shutdown.
    • Recovery Process: After power is restored, the device will automatically restart and stand by. The previous print job is aborted, and you need to manually start a new print.

  • Power Loss Recovery

    • Concept: When an abnormal power loss is detected, the system immediately saves the current print progress (e.g., position, layer height), then shuts down.
    • Recovery Process: After power is restored, user confirmation is typically required before the device can resume and complete the unfinished print from the point of interruption.

2. Core Rules

  • Power Loss Shutdown and Power Loss Recovery are mutually exclusive functions and cannot be enabled simultaneously.
  • If the Power Loss Shutdown function is enabled, the Power Loss Recovery function will automatically become ineffective.

3. How to Choose

  • Choose "Power Loss Shutdown": If you are more concerned about electrical safety, or want the device to automatically start up and stand by after power is restored without needing to resume an interrupted print, enable this function.
  • Choose "Power Loss Recovery": If you frequently perform long, critical print jobs that cannot afford to fail and wish to resume printing from the interruption point after a power loss, enable this function.

Wiring​

Important Precautions
  • FLY Pi-V2 Power Loss Shutdown/Recovery Function Notes
  • When connecting to other host computers via USB, the 5V power line must be disconnected or isolated (e.g., by cutting the cable or using a USB cable with only data pins)
  • Power must be supplied using the dedicated KPPM module. Do not use other power supply methods.
  • If the 5V connection between the mainboard and the host computer cannot be disconnected, the mainboard must be completely powered off before it can be restarted. Otherwise, it may fail to boot normally.
  • FLY-Pi using 5V wiring
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Configuration​

Disable Power-Off Shutdown​

Note
  • Power-off shutdown must be disabled; otherwise, power-loss resume printing will not work.
  • There is an auto-shutdown function after saving progress during power-loss resume printing.
  • Ensure no other power source is connected to the host, otherwise it will not be able to power on.

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

  • Access the configuration page

    • Open the device IP address in the browser, for example: http://192.168.1.2/
    • In Fluidd, as shown on the left side of the image below, uncheck -> Filter hidden files and folders.
    • In Mainsail, as shown on the right side of the image below, check -> Show hidden files.
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    • At this point, you can see the .flyos-config folder. Entering this folder will reveal a sys-config.conf file.
    • The sys-config.conf file is a symlink to the configuration file config.txt in the removable disk FlyOS-Conf.
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    • Open the sys-config.conf file and find the two configurations: shutdown_pin_state and shutdown_pin=
    • Add # before both of these configurations
    • Then Save -> Close and restart the device.
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plr.cfg Configuration File​

  • On the printer configuration page, locate the plr.cfg file.
  • Clear its contents, then paste the configuration below into it.
  • The configuration file content is as follows:
[mcu host]
serial: /tmp/klipper_host_mcu

[power_loss_resume]
power_pin: host:gpiochip1/gpio21
is_shutdown: True # Whether to perform shutdown operation, default is enabled
paused_recover_z: -2.0 # Z-axis movement distance when resuming from a paused print, default is no movement
start_gcode:
    # G-code executed before resuming printing
    # All parameters saved before power loss can be accessed via {PLR}
    # Use M118 {PLR} to output all available parameters
    # M118 {PLR}
    M118 Resuming print: {PLR.print_stats.filename}
    M118 Interruption 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 %}
    G91                             ; Relative positioning
    G1 Z2 F100                      ; Lift Z, prepare for X, Y homing
    G90                             ; Absolute positioning
    G28 X Y                         ; Home X and Y
    M83                             ; Relative extrusion
    # G1 E0.5 F400                   ; Extrude a small amount
layer_count: 2 # Execute layer_change_gcode after resuming the specified number of layers
layer_change_gcode:
    # G-code to execute after resuming {layer_count} layers
    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:
    # G-code executed before shutdown
    M118 Low power voltage, shutting down
    # M112 ; Emergency stop

  • After saving the configuration file above

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


    [include plr.cfg]

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

  • At this point, the Klipper power loss recovery function has been configured.

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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