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MVP Functional Requirements — 3D Printer Control Firmware

Architecture

┌─────────────────────────────────────────────────────────────────┐
│  Portable library crates (no_std, test on host + WASM)         │
│                                                                 │
│  ┌──────────────┐  ┌──────────────┐  ┌────────────────────┐   │
│  │ gcode-parser │  │  dispatcher  │  │  motion-planner    │   │
│  │  (pure parse)│  │ (cmd routing)│  │  + step_generator  │   │
│  └──────────────┘  └──────────────┘  └────────────────────┘   │
│                                                                 │
│  ┌──────────────┐  ┌──────────────┐  ┌────────────────────┐   │
│  │   thermal    │  │    sdcard    │  │  actor-framework   │   │
│  │  (PID + mgr) │  │ (line reader)│  │  (mailbox, select) │   │
│  └──────────────┘  └──────────────┘  └────────────────────┘   │
│                                                                 │
│  ┌──────────────────────────────────────────────────────────┐  │
│  │  printer-hal  (trait definitions — no implementations)   │  │
│  └──────────────────────────────────────────────────────────┘  │
└─────────────────────────────────────────────────────────────────┘

┌───────────────────────────┐  ┌───────────────────────────┐
│  firmware/ (binary)       │  │  firmware-pico/ (binary)   │
│  Duet 3 ATSAME54 HAL     │  │  BTT SKR Pico RP2040      │
│  board-hal pin mappings   │  │  board-pico pin mappings   │
│  Embassy executor spawn   │  │  4x TMC2209 shared UART   │
│  Full mainboard stack     │  │  Full mainboard stack      │
└───────────────────────────┘  └───────────────────────────┘

┌───────────────────────────┐  ┌──────────────────────────────┐
│  firmware-ebb42/ (binary) │  │  wasm-sim/ (binary/lib)      │
│  BTT EBB42 STM32G0B1     │  │  Browser mock HAL impls      │
│  board-ebb42 pin mappings │  │  Embassy arch-wasm32         │
│  CAN toolboard (subset)  │  │  Canvas rendering, WebSerial │
│  Stepper + thermal + CAN │  │  No hardware dependencies    │
└───────────────────────────┘  └──────────────────────────────┘

Supported Boards

Board MCU Role Crate Firmware
Duet 3 Mini 5+ Ethernet ATSAME54P20A (Cortex-M4F, 120MHz) Mainboard board-hal firmware/
BTT EBB42 v1.2 STM32G0B1CBT6 (Cortex-M0+, 64MHz) CAN Toolboard board-ebb42 firmware-ebb42/
BTT SKR Pico v1.0 RP2040 (dual Cortex-M0+, 133MHz) Mainboard board-pico firmware-pico/

MVP Checklist

1. Motion Control

  • G-code parsing (G0, G1, G28, G90, G91, G92)
  • Trapezoidal acceleration planner
  • Multi-axis Bresenham step distribution
  • Per-axis feedrate and acceleration clamping
  • Absolute / relative positioning modes
  • Homing state tracking
  • Emergency stop (M112) — immediate queue clear
  • Wait for moves (M400)
  • Position reporting (M114)
  • Endstop reading (homing actually hits a switch)
  • Software endstops (min/max travel limits)
  • Backlash compensation (optional)

2. Pressure Advance

Linear advance for extruder pressure compensation. Adjusts extruder steps ahead of actual motion to compensate for filament compression in the Bowden tube or hotend melt zone.

  • Pressure advance factor (K) storage per extruder (M572)
  • Extruder step lookahead — advance E steps based on instantaneous speed
  • Deceleration compensation — retract extra E steps on deceleration
  • G-code: M572 D0 S0.06 — set advance factor per extruder
  • Per-segment E-step adjustment in step generator
  • Unit tests: verify E steps lead/lag XY motion by K × velocity

3. Input Shaping / Dynamic Speed Control

Reduce ringing (ghosting) artifacts by filtering acceleration profiles to cancel resonant frequencies of the printer frame and toolhead.

  • Input shaper filter (ZV, MZV, EI, 2HUMP_EI, 3HUMP_EI types)
  • Configurable shaper frequency per axis (M593)
  • Configurable damping ratio per axis
  • Shaped acceleration profile generation (pre-filter trapezoid into shaped segments)
  • G-code: M593 F45.0 — set input shaper frequency
  • G-code: M593 P"mzv" — select shaper type
  • Acceleration limit adjustment based on shaper (max_accel × shaper_factor)
  • Dynamic speed scaling — reduce speed at sharp corners to limit vibration
  • Unit tests: verify shaped profile has correct number of impulses
  • Unit tests: verify frequency response attenuation at resonant frequency

4. Thermal Management

  • PID controller with anti-windup
  • Bed + dual hotend heater channels
  • Thermal runaway detection
  • Temperature set (M104) and set-and-wait (M109)
  • Bed temperature set (M140) and wait (M190)
  • Fan speed control (M106 / M107)
  • Actual ADC thermistor reading (HAL trait)
  • Actual PWM heater/fan output (HAL trait)
  • PID auto-tune (M303)

5. Configuration

  • Steps per mm (M92)
  • Max feedrate (M203)
  • Max acceleration per axis (M201)
  • Default print/travel acceleration (M204)
  • Microstepping (M350)
  • Motor current (M906)
  • Driver direction/mode (M569)
  • Built-in config defaults
  • SD card config load (CONFIG.G)
  • Config save/restore (M500/M501)

6. SD Card / File I/O

  • Line reader (zero-allocation line parser)
  • SD card actor message protocol
  • SPI init + FAT32 mount (HAL trait)
  • Stream G-code file for job execution
  • Job pause / resume / cancel
  • Job progress reporting

7. Communication

  • USB serial G-code input
  • Serial response output (ok, error, temperature reports)

8. CAN Toolboard Support (CBOR)

CAN-FD bus for distributed tool boards (e.g., Duet 3 1HCL, 3HC, toolboard 1LC). Uses CBOR encoding for compact, schema-flexible messages over CAN frames.

  • CAN-FD driver (1 Mbit arbitration, 5 Mbit data phase)
  • CBOR message serialization/deserialization (no_std, zero-alloc)
  • Toolboard discovery and address assignment protocol
  • Remote heater control — set target temp, read current temp via CAN
  • Remote stepper control — send step/dir commands to toolboard drivers
  • Remote endstop reading — poll toolboard endstop state
  • Remote thermistor reading — stream ADC values over CAN
  • Remote fan control — set fan PWM via CAN
  • Heartbeat / watchdog — detect toolboard disconnect
  • printer-hal trait proxying — wrap CAN transport as HAL trait impls
  • G-code: M954 — configure CAN toolboard mapping
  • Unit tests: CBOR encode/decode roundtrip
  • Unit tests: mock CAN transport with loopback

9. Hardware Abstraction (printer-hal traits)

  • StepperDriver — set direction, pulse step, enable/disable
  • TemperatureSensor — read temperature from ADC channel
  • HeaterOutput — set PWM duty cycle for heater/fan
  • FileSystem — open/read/close files from storage
  • EndstopReader — read endstop switch state
  • Delay — microsecond-precision timing for step pulses

10. Actor System

  • Typed mailboxes (embassy-sync channels)
  • System event bus (pub/sub broadcast)
  • Priority-based select (select, select3)
  • Dispatcher → planner → step generator pipeline
  • Thermal manager 10Hz PID loop
  • Status monitor (aggregates all actor outputs)

11. WASM Simulation Target

  • Mock StepperDriver — logs steps, tracks position
  • Mock TemperatureSensor — simulated thermal model
  • Mock HeaterOutput — records duty cycles
  • Mock FileSystem — reads from embedded strings or JS
  • Mock EndstopReader — configurable trigger state
  • Embassy arch-wasm32 executor
  • Browser entry point (wasm-bindgen)
  • Simulated time (embassy-time with wasm tick source)

12. Portability Requirements

  • All business logic in no_std library crates
  • Library crates depend only on printer-hal traits (not board-hal)
  • Firmware binary: only hardware init + task spawn + HAL impl wiring
  • Unit tests run on host (x86_64-unknown-linux-gnu)
  • WASM target compiles with mock HAL

13. Safety

  • Thermal runaway detection
  • Emergency stop propagation to all actors
  • Watchdog timer (hardware reset on firmware hang)
  • Heater interlock (max on-time without temp change)
  • Stepper timeout (disable after idle period)