PicoFaceCP

A Yamaha Reface CP emulation for the Raspberry Pi RP2350 (16 MB flash).

PicoFaceCP turns an RP2350 board into a compact electric-piano module: the mda‑EPiano sound engine drives six classic electric‑piano voices, processed through a faithful re‑creation of the Reface CP insert‑effect chain, and controlled from an SH1106 OLED and three rotary encoders (Selector, Param A, Param B). A macOS host build lets you develop and audition the whole signal path on your desktop before flashing hardware.

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Features

• 6 voices (mda‑EPiano sample engine, 96‑voice polyphony, 44.1 kHz, stereo): Rd I · Rd II · Wr · Clv · Piano · CP
• Reface CP effect chain — four insert effects in series plus drive & volume, with authentic 3‑position switching per block and voice‑type‑linked tremolo.
• USB‑MIDI, reface CP‑compatible — Note On/Off, Pitch Bend (±2 semitones), the full reface CP Control Change map (Modulation, Volume, Expression, Sustain/Sostenuto/Soft Pedal, per‑effect switches & depths, instrument select), Channel Mode Messages, Active Sensing, and SysEx (Identity Reply, Parameter Change/Request, Bulk Dump/Request). Program Change is not recognized, matching the original hardware. Full spec: doc/MIDI_IMPLEMENTATION.md.
• Paged front‑panel UI (SH1106 + three encoders) — the Selector encoder pages through eight parameter screens (VOL/OCT · VOICE · TREM/WAH · CHO/PHA · DLY · REVERB · V.PARAMS · SYSTEM); Param A and Param B set the two on‑screen values. A short Selector press cycles the effect mode on the TREM/CHO/DLY screens; a long press opens the Presets / System menu. Octave (−2..+2) transpose lives on the first screen; MIDI receive channel and Pre‑Gain live on the last (SYSTEM).
• Pre‑Gain — an extra stage ahead of Drive lets you attenuate the signal feeding the FX chain, since some effects (Drive, Wah) tend to clip hot signals.
• Header‑only, RP2350‑optimized DSP — single‑precision float throughout (engine and effects), no heap, the per‑sample hot path placed in RAM to avoid XIP‑cache jitter inside the audio IRQ.
• Virtual EEPROM settings persistence — knobs, instrument, octave, MIDI system settings survive power cycles, autosave 2 s after last change; see doc/PERSISTENCE.md.
• macOS host demo (CoreAudio + PortMidi) running the exact same effect code.

Current firmware footprint: FLASH ≈ 26.4 % (≈ 4.4 MB / 16 MB), RAM ≈ 33.8 % (≈ 169 KB / 512 KB).

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Signal flow

              ┌──────────┐   ┌────────┐   ┌──────────────┐   ┌───────────────┐   ┌─────────────────┐   ┌────────┐
MIDI ▶ Voice ▶│ PRE‑GAIN │ ▶ │ DRIVE  │ ▶ │ TREMOLO / WAH│ ▶ │ CHORUS /PHASER│ ▶ │ D.DELAY/A.DELAY │ ▶ │ REVERB │ ▶ VOLUME ▶ I2S out
       engine └──────────┘   └────────┘   └──────────────┘   └───────────────┘   └─────────────────┘   └────────┘

Block	Switch positions	Parameters
Pre‑Gain	—	level (PicoFaceCP‑only, no reface CC equivalent; avoids FX clipping)
Drive	—	amount
1 · Tremolo / Wah	Off / Tremolo / Wah	Depth, Rate
2 · Chorus / Phaser	Off / Chorus / Phaser	Depth, Speed
3 · D.Delay / A.Delay	Off / Digital / Analog	Depth, Time
4 · Reverb	—	Depth
Volume	—	output level

The tremolo automatically follows the selected voice, exactly like the hardware: auto‑pan for Rd I / Rd II / CP, amplitude modulation for Wr / Clv / Piano. The reference for these effects is the official manual (doc/ZT92080_reface_En_OM_C0.pdf, "reface CP" section).

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Hardware

Default target board: SparkFun Pro Micro RP2350 (PICO_BOARD in CMakeLists.txt; change it for your own board). Audio output uses an I2S DAC (e.g. Waveshare Pico‑Audio).

Function	GPIO	Notes
I2S DATA (DOUT)	26	PICO_AUDIO_I2S_DATA_PIN
I2S BCLK	27	PICO_AUDIO_I2S_CLOCK_PIN_BASE
I2S LRCLK (WS)	28
OLED SDA	2	SH1106 128×64 over I2C
OLED SCL	3
Selector encoder CLK	6	screen / menu navigation
Selector encoder DT	7
Selector encoder SW	8	short press: cycle effect mode · long press: menu
Param A encoder CLK	10	sets on‑screen value A
Param A encoder DT	11
Param A encoder SW	14	optional — press resets value A to default
Param B encoder CLK	12	sets on‑screen value B
Param B encoder DT	13
Param B encoder SW	15	optional — press resets value B to default
Status LED	25
DIN‑MIDI RX	5	optional

Pins are defined in include/project_config.h.

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Repository layout

effects/              Reface CP effect chain (header-only)
  dsp_fastmath.h        fast tanh/tan approximations
  dsp_lut.h             sine lookup table
  dsp_reverb.h          Schroeder stereo reverb
  reface_cp_fx.h        Tremolo / Chorus / Phaser / Delay primitives
  wahwah.h              standalone MK8 touch-wah
  reface_cp_chain.h     RefaceCpChain master class (setters + getters)
  cp_hot.h              CP_HOT() RAM-placement macro (Pico) / no-op (host)
  cp_audio.h            int16 <-> float block glue
  effect_chain.{h,cpp}  Rhodes MK8 reference chain (source of WahWah)
include/              engine, UI, board and config headers
src/                  main.cpp, mdaEPiano engine, USB-MIDI transport, OLED/encoder UI
  midi_reface.{h,cpp}     reface CP MIDI protocol layer (CC map, SysEx, Active Sensing)
  pico_frontpanel.{h,cpp}  virtual front‑panel UI (home screen + main menu)
test/                 macOS host demo (cp_test.cpp, build_cp.sh)
doc/                  Reface owner's manual + MIDI Data List (PDF)
  MIDI_IMPLEMENTATION.md   PicoFaceCP MIDI spec (reface CP Data List equivalent)
  CHANGELOG_MIDI_RP2350.md MIDI layer + RP2350 float-math changelog
lib/                  pico-sdk, pico-extras, FreeRTOS-Kernel (submodules), u8g2, ...

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Building the firmware

Requires the Arm GNU toolchain (arm-none-eabi-gcc), CMake ≥ 3.22 and Ninja (or Make).

# 1. Clone with submodules (pico-sdk, pico-extras, FreeRTOS-Kernel)
git clone --recurse-submodules https://github.com/Michi71/PicoFaceCP.git
cd PicoFaceCP
# (if already cloned: git submodule update --init --recursive)

# 2. Configure & build
cmake -S . -B build -G Ninja
cmake --build build -j4

Flash build/main.uf2 by holding BOOTSEL while plugging in the board and copying the file to the RPI-RP2 drive (or use picotool load build/main.uf2).

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macOS host demo

Build and run the full engine plus the Reface CP effect chain natively, with audio through CoreAudio and MIDI through a virtual PortMidi input named mdaepiano.

brew install portmidi
./test/build_cp.sh
./test/cp_test

Point any DAW / MIDI tool at the mdaepiano virtual port to play it.

The original engine‑only demo (test/test.cpp, ./test/build.sh, test/mdaepiano_test) is kept alongside it for reference.

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Controls

On the device (OLED + 3 encoders)

The front panel uses three rotary encoders: the Selector encoder moves between screens and navigates menus, while Param A and Param B edit the two values shown on the current screen. Each value screen looks like:

 TREM: Tremolo   3/7   <- header: title (+ current mode) and page number
 ------------
 Depth 25
 Rate  60
 Sel:Mode  A/B:edit    <- hint line

• Turn the Selector to step through the 8 screens:
  1. VOL / OCT — master Volume (A) and Octave −2..+2 (B). Octave is a Core‑1 note transpose applied before synthesis.
  2. VOICE — Voice Type (A) and Drive (B).
  3. TREM / WAH — Depth (A) and Rate (B).
  4. CHO / PHA — Depth (A) and Speed (B).
  5. DLY — Depth (A) and Time (B).
  6. REVERB — Reverb depth (A).
  7. V.PARAMS — scroll the mda‑EPiano parameter list with A, edit the selected value with B.
  8. SYSTEM — MIDI receive channel (A, 1‑16 or All) and Pre‑Gain (B, 0‑100 %, applied ahead of the FX chain).
• Short press the Selector on the TREM / CHO / DLY screens to cycle that effect's mode (Off → A → B): Off→Tremolo→Wah, Off→Chorus→Phaser, Off→Digital→Analog. The header shows the active mode.
• Long press the Selector (≥ 0.5 s) opens the main menu: Presets · System · << BACK.
• Param A / Param B set the two on‑screen values live; pressing their optional switch resets that value to a default.

Note: changing the Octave while keys are held can leave a held note hanging (note‑off is transposed by the current octave) — release keys before switching octaves.

Host demo keyboard

Key	Action
+ / -	program up / down
1…5	select program directly
i	next voice (Rd I → Rd II → Wr → Clv → Piano → CP)
t	Tremolo/Wah: off → tremolo → wah
c	Chorus/Phaser: off → chorus → phaser
d	Delay: off → digital → analog
r	Reverb on/off
s	sustain pedal (CC64)
m	mod wheel (CC1) → 127
q	quit

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Design notes (RP2350)

• Header‑only DSP, no dynamic allocation — everything lives in fixed buffers and compiles for both the Cortex‑M33 firmware and the host build.
• Hot path in RAM — cp_hot.h maps CP_HOT() to the Pico SDK's __not_in_flash_func, so the per‑sample chain (RefaceCpChain::process, which the compiler inlines the whole chain into) runs from SRAM and avoids flash XIP‑cache stalls in the I2S interrupt; on the host the macro is a no‑op.
• int16 delay line — the 500 ms stereo delay stores int16 samples, which is lossless relative to the 16‑bit engine source and roughly halves its RAM use.
• Single‑precision float throughout the audio path (the M33 has a hardware FP unit; double is avoided) — this includes mdaEPiano's note‑on/off envelope and pitch math (exp/pow/sqrt → expf/powf/sqrtf), which runs inside the audio DMA IRQ via the Core‑0 IPC queue.
• Virtual EEPROM in last 8 KB flash, wear‑leveled 256‑B CRC record log; Core 0 parks in RAM spin via IPC_CMD_FLASH_LOCK during writes (flash_safe_execute would collide with SIO‑FIFO IPC).

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Acknowledgements & license

• Sound engine: mda‑EPiano © Paul Kellett / David Robillard (GPL).
• Reface CP behaviour modelled from Yamaha's official owner's manual.
• DSP and UI code for the effect chain were developed with an LLM‑assisted workflow (architecture/review here, code generation via glm‑5.2).

Licensed under the GNU General Public License v3 — see LICENSE.