Understanding MMU State¶

Before moving filament or recovering from a problem, it helps to separate four questions:

Run without any modifying parameters, all four are read-only reports. Taken together, they distinguish a configuration problem from an incorrect map, stale tracked state, or a physical sensor that disagrees with reality.

A Box Turtle snapshot¶

The following snapshot is from a four-gate Box Turtle. T0 and gate 0 are selected, filament is preloaded and parked in every gate, and no filament is loaded into the bowden or extruder. Your report will differ with the MMU design, fitted sensors, calibration, maps, and current filament position.

Machine state and configured sequences¶

MMU_STATUS SHOWCONFIG=1

MMU: Happy Hare v4.0.0 controlling 1 units:
● BoxTurtle-0, a BoxTurtle v1.0 (gates 0-3)
└ Connected to extruder: extruder
└ Selector Type: VirtualSelector.

Print state is INITIALIZED. Tool T0 selected on gate #0
MMU gear stepper at 100% current and is NOT SYNCED to extruder
Sync feedback indicates filament in bowden is: TENSION (not currently active)
Filament positon believed to be: UNLOADED AND PARKED

PRELOAD SEQUENCE:
- Filament preloads by homing a maximum of 200.0mm (gate_preload_homing_max) to MMU_EXIT sensor, with up to 2 attempts
- Filament is parked by moving 10.0mm (gate_preload_parking_distance) from the preload endstop
- RFID/NFC scanning during preload is OFF; no per-gate readers are configured

LOAD SEQUENCE:
- Filament loads into gate from parked position by homing a maximum of 300.0mm (gate_homing_max) to mmu_shared_exit sensor
- Bowden is loaded with a fast 680.0mm (calibrated_bowden_length:700.0 - bowden_load_homing_buffer:20.0) move
- Filament finds extruder entrance by homing a maximum of 120.0mm (bowden_load_homing_buffer:20.0 + extruder_homing_max:100.0) to FILAMENT_COMPRESSION sensor and then moving -4.0mm (buffer_range:8.0 / 2) to center sync-feedback buffer
- Extruder (synced) loads by moving 68.0mm (toolhead_extruder_to_nozzle:72.0 - toolhead_residual_filament:2.0 - toolhead_ooze_reduction:0.0 - toolchange_retract:2.0 - filament_remaining:0.0) to the nozzle
- Purging is always managed by Happy Hare using '_MMU_PURGE' macro with extruder purging current of 100%
- Filament in bowden will be adjusted a maximum of 8.0mm to neutralize tension

UNLOAD SEQUENCE:
- Tip is always formed by Happy Hare using '_MMU_FORM_TIP' macro after initial retract of 2.0mm (toolchange_retract) with extruder current of 100%
- Extruder (optionally synced) unloads by moving 82.0mm (toolhead_extruder_to_nozzle:72.0 + toolhead_unload_safety_margin:10.0) less tip-cutting reported park position to exit extruder
- Bowden is unloaded with a fast 660.0mm (calibrated_bowden_length:700.0 - bowden_unload_homing_buffer:40.0) move
- Filament finds gate by homing a maximum of 340.0mm (bowden_unload_homing_buffer:40.0 + gate_homing_max:300.0) to mmu_shared_exit sensor
- Filament is parked by moving -100.0mm (gate_parking_distance) from the gate endstop (mmu_shared_exit sensor)

For details on TTG and EndlessSpool groups add 'DETAIL=1'

Gate : | 0 | 1 | 2 | 3 |
Tools: |T0 |T1 |T2 |T3 |
Avail: |■■■|■■■|■■■|■■■|
Selct: |\▼/|~~~~~~~~~~~~ T0
[T0] ■◉■■◉■┈◯┈┈┈┈┈┈┈┈ [◁ ▷] ┈┈┈┈┈┈┈Ex┈┈┈┈┈┈┈┤Nz UNLOADED 50.0mm

The report has three layers:

• Machine and active state identifies the MMU unit, attached extruder, selector type, print state, selection, motor synchronization, sync-feedback state, and tracked filament position.
• Preload, load, and unload sequences describe the exact decisions and calculated distances the current setup will use. The parameter names and values in parentheses make this especially useful while tuning. A different sensor layout can produce a substantially different route.
• Compact state display relates gates, tools, availability, selection, and tracked filament position. Here the selection marker is under gate 0, T0 maps to that gate, and the final line shows filament parked at the gate rather than loaded through the bowden.

Add DETAIL=1 when you also want the Tool-to-Gate map and EndlessSpool groups included in the status report:

MMU_STATUS SHOWCONFIG=1 DETAIL=1

Reading the compact state displays¶

The compact table and filament-path line answer different questions. The table covers every unit and gate; the path line covers only the currently selected tool and gate. Read the table first to establish the selection, then read the path from the selected gate on the left toward the nozzle on the right.

The following two examples are independent snapshots: the table has T8 selected, while the path line begins with T9.

Unit, gate, tool, and availability table¶

Unit : ----------------- unit0 -----------------   ----- unit1 -----
Gate : | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 |Byp|   | 9 | 10| 11| 12|
Tools: |T0 |T1 |T2 |T3 |T4 |T5 |T6 |T7 |T8 | - |   |T9 |T10|T11|T12|
Avail: |■■■|■■■| - |■■■|■?■|■?■|■■■|■?■|■?■|   |   |■■■|■■■| - | - |
Selct: ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~|\▼/|~~~~   ~~~~~~~~~~~~~~~~~ T8

Each four-character column describes one physical gate:

The availability cells use the center character to distinguish state:

In the selection row, ~ means that unit's selector is homed and X means it is not homed. |\▼/| points at the active physical gate; the triangle is rendered in that gate's filament color when possible. In this snapshot gate 8 is selected on unit0, its TTG mapping is T8, and unit1 has no selected gate. The table also shows gates 2, 11, and 12 as empty, gates 4, 5, 7, and 8 as unknown, and the remaining gates as available.

Filament position line¶

[T9] ■◉■■◉■┈┈┈┈┈┈┈┈┈┈ [◁ ▷] ┈┈┈┈┈┈┈Ex┈┈┈◯┈┈┈┤Nz UNLOADED 0.0mm

Read this from left to right:

This example says that T9 is selected, filament is parked across the fitted gate sensors, and nothing extends into the bowden, extruder, or nozzle. The toolhead sensor is open. The tension-side buffer switch is physically triggered, but the empty center of [◁ ▷] shows that sync feedback is inactive because filament is not loaded through the buffer.

What is loaded in each gate¶

MMU_GATE_MAP describes the physical gates. Availability and filament attributes belong to a gate even when the TTG map sends a differently numbered tool there.

MMU_GATE_MAP

Gates / Filaments:
0 (■■■) [T0]:    On spool;  TPU   | 226°C | #14BA5E | Prusa TPU HF [SELECTED]
1 (■■■) [T1]:    On spool;  TPU   | 240°C | #9B4BCE | Prusa TPU Silk
2 (■■■) [T2]:    On spool;  PLA+  | 228°C | #474EE2 | KVS PLA+ Matte
3 (■■■) [T3]:    On spool;  ABS   | 229°C | #4B3E86 | Bambu Labs ABS Basic

Each row identifies the physical gate, availability, mapped tool, material, temperature, color, and filament name. [SELECTED] agrees with the gate 0 selection in MMU_STATUS. Depending on your integrations and settings, the report can also include Spoolman, RFID, and speed-override information.

If the filament attributes are wrong but the physical sensors are correct, the gate map is the layer to fix. See Gate/TTG Maps for updating it directly or through Spoolman.

Which gate each tool will use¶

Slicer g-code requests logical tools (T0, T1, and so on); the TTG map resolves each request to a physical gate.

MMU_TTG_MAP

TTG Map:
T0 -> Gate 0(■■■) [SELECTED]
T1 -> Gate 1(■■■)
T2 -> Gate 2(■■■)
T3 -> Gate 3(■■■)

This is a straight-through map: each tool uses the same-numbered gate. A remapped printer might instead show T0 -> Gate 3; that is valid and does not mean the gate map is wrong. Use MMU_TTG_MAP DETAIL=1 to include EndlessSpool groups.

What the sensors see¶

MMU_SENSORS reports the raw state of every fitted filament sensor. The names and number of sensors depend on the hardware.

MMU_SENSORS

filament_compression  --> Open
filament_tension      --> TRIGGERED
mmu_entry_0           --> TRIGGERED
mmu_entry_1           --> TRIGGERED
mmu_entry_2           --> TRIGGERED
mmu_entry_3           --> TRIGGERED
mmu_exit_0            --> TRIGGERED
mmu_exit_1            --> TRIGGERED
mmu_exit_2            --> TRIGGERED
mmu_exit_3            --> TRIGGERED
mmu_shared_exit       --> Open

In this snapshot, the entry and exit sensors for every gate are triggered, which is consistent with all four filaments being preloaded and parked. The shared exit is open, consistent with nothing entering the bowden. The sync-feedback tension switch is triggered, but MMU_STATUS explicitly says feedback is not currently active because no filament is loaded through it.

Treat a sensor report as physical evidence, not as a command to change Happy Hare's tracked state. If a sensor reading is unexpected, inspect the filament and switch first. The Sensors page covers naming, testing, and temporarily disabling a faulty sensor.

Cross-checking the reports¶

The most useful information is often where two views agree—or fail to:

If the reports disagree:

• Run MMU_CHECK_GATE to physically check filament presence and refresh gate availability.
• Use MMU_RECOVER when the tracked selection or filament position does not match reality.
• Correct MMU_GATE_MAP when the spool attributes or availability are wrong, and MMU_TTG_MAP when a tool points to the wrong gate.
• Investigate an unexpected MMU_SENSORS reading as a filament, wiring, or switch problem before disabling that sensor.

See also¶

• Operation
• Feature: Gate/TTG Maps
• Feature: Sensors
• Feature: State Persistence
• Command Reference