This plugin adds Prusa MMU support to OctoPrint. The active filament will be displayed in the navbar and you will be prompted to select which filament to use when slicing in "MMU Single" mode. Other settings are available to name each tool and set defaults. This plugin only works for Prusa printers with an MMU. Supports MMU firmware 1.X.X and 3.X.X.

  • Displays MMU state in the navbar (configurable)
  • (Optional) Default to a filament if none are selected
  • On single color prints, shows a modal to select the filament within Octoprint
  • Displays an error popup when the MMU throws an error (Only when running 3.0.0+)
  • Supports retrieving filament data from Spool Manager and Filament Manager if installed.

GCode Interactions

This plugin does some minimal gcode manipulation. This is how it detects tool events and pause the print to provide the dialog.

The command interactions are as follows:

  • Before sent: (gcode_queuing_hook)
    • Tx: When the GCODE would send a Tx (tool change) it first triggers the modal and then does not send the Tx command. Instead, it sends a pause event to the printer. This results in Prusa not prompting for a tool change. If the timeout time is reached (_timeout_prompt) then the plugin resends the Tx command to allow Prusa to prompt the user.
    • M109: When the GCODE would send an M109 (Wait for Hotend Temperature) and the user has selected a filament it sends both the M109 and T# (like T2), otherwise it just sends the M109.
  • After sent: (gcode_sent_hook)
    • When the plugin notices a T# command it sets the tool internally, so it can be used to display. This is to support multicolor printing. This trigger is also used to show unloading.

MMU2 1.X.X

It listens to printer responses and does some substring matching. This is done to identify filament events and printer notifications, so it can update the navbar: (gcode_received_hook)

  • paused for user - Used to show that the printer needs attention (either error or waiting for tool selection at printer).
  • MMU not responding - Used to show that the printer needs attention because of an MMU failure.
  • MMU - ENABLED / MMU starts responding - Used to show printer is “OK”.
  • MMU can_load / Unloading finished - Used to show the filament loading message.
  • OO succeeded - Used to show what filament is loaded.

MMU2/3 3.X.X

The MMU 3.X.X firmware communicates continuously with the printer. The printer sends the MMU requests, and the MMU sends back responses. The MMU’s responses start with the request letter and data, so it just listens for the Responses.

MMU 3.X.X responses come in this format:
MMU2:<(Request Letter)(Request Data) (Response Letter)(Response Data)

  • (Request Letter) - A single letter code that represents a request sent from the printer to the MMU.
    • It only listens for T - Tool, L - Load, U - Unload, X - Reset, K - Cut, and E - Eject.
  • (Request Data) - Hexidecimal data that follows the Request Letter.
    • It’s usually 0, unless the request involves filament, in which case it is the filament number [0-4].
  • (Response Letter) - A single letter code that represents a response from the MMU.
    • Possible responses are P - Processing, E - Error, F - Finished, A - Accepted, R - Rejected, and B - Button.
  • (Response Data) - Hexidecimal data that follows the Response Letter.
    • The amount of data varies depending on the Request Letter and Response Letter.
    • We only use Response Data to decode P - Progress messages, and E - Error messages

Several Regex strings are used to parse the MMU 3.X.X responses:

  • MMU2:<[TLUXKE] - Generic Regex used to catch the responses with the Request Letters that are important.
  • MMU2:<([TLUXKE])(.*) ([PEFARB])(.*)\* - Used to split the command into the four groups described above.

Additionally, it also listens for these lines:

  • MMU2:Saving and parking - Used to detect when the printer is waiting for user input after the MMU fails at auto-retrying after an Error.
  • MMU2:Heater cooldown pending - The same as above. Might be unnecessary, but included just in case.
  • LCD status changed - If the printer was paused, this indicates that the pause is probably over.

For all instances where command manipulation happens see for Gcode Hooks. Also look at function _timeout_prompt where it handles unpausing the printer after the timer and either sending a Tx or T# if useDefaultFilament and defaultFilament settings are set.

More documentation is available here.

Known Bugs

  1. In rare instances, the “waiting for user input” event can come in directly after a tool change is sent, resulting in the navbar never updating. This will not impact printing, but you will see “Awaiting user input” until the next tool change.
  2. If the Prusa printer prompts the user for a “new version”, the select filament modal may not display. You will still be able to select the filament directly on the printer.


Dialog that opens to select the filament to use.
Navbar showing the MMU state.
An error popup on MMU failure.
Settings configuration options.