22 Microcontroller

STM32H7

This page documents the current state of zicBox running on STM32H7 microcontrollers.
The implementation serves as a proof of concept (POC) demonstrating that zicBox can run efficiently on a modern MCU with real-time audio synthesis capabilities.

Overview

zicBox has been successfully ported to the STM32H7 family and is currently running on a WeActStudio MiniSTM32H723 board.

The goal of this work is to validate STM32H7 as a solid platform for:

• Real-time drum synthesis
• Low-latency audio output
• Embedded UI (display + encoder)
• Future expansion toward sample playback and modular synth (Eurorack) compatibility

At this stage, the system is functional but still requires significant work to become feature-complete.

Hardware Platform

• MCU: STM32H723
• Board: WeActStudio MiniSTM32H723
• Core: Cortex-M7
• Clock: High-frequency internal + PLL
• DAC: Built-in 12-bit DAC
• ADC: Multiple 16-bit ADCs
• Storage:
  • On-chip SPI Flash (for settings)
  • Built-in SD card interface
  • OSPI Flash (for sample playback)

Tip

Since zicBox runs successfully on STM32H7, it will most likely also run on other platforms based on the same MCU family, such as Daisy Seed and KORG NTS-1 mk2.

These platforms share similar characteristics Cortex-M7 core and high-performance DSP capabilities.

While board-specific adaptations would still be required (audio I/O, storage, UI, pin mapping), the current STM32H7 port demonstrates that zicBox’s architecture is compatible with this class of embedded audio hardware.

Current Features

Audio Engine

• One active drum voice engine running in real time
• Support for multiple drum engine types (architecture in place)
• Audio output via built-in 12-bit DAC
• Audio quality is sufficient for:
  • Drum synthesis
  • Percussive sounds
  • Embedded drum machine use cases

Despite the DAC being limited to 12-bit, it sound great for this application.

User Interface

• Display is fully operational
• Rotary encoder support
• Basic navigation and parameter control working
• UI loop integrated with the audio engine without audible glitches

Performance

• Real-time synthesis runs reliably on STM32H7
• No noticeable audio dropouts under current load
• Confirms STM32H7 is powerful enough for multi-voice drum synthesis

Work in Progress / Planned Features

Persistent Storage

• Persisting settings in on-chip SPI Flash
• Presets, configuration, and state restoration

Sample Playback

• SD card support for loading samples
• Preloading samples into OSPI Flash
• Hybrid engine:
  • Synthesized drums
  • Sample-based playback

Eurorack Compatibility

• Add output op-amp stage
  • Match Eurorack signal levels
  • Improve output impedance and signal quality

Control Voltage (CV) Input

• Use built-in 16-bit ADCs
• Multiple CV inputs
• Target use cases:
  • Trigger inputs
  • Modulation (pitch, decay, timbre, etc.)
  • External clock / sync

Current Limitations

• Single active drum voice at the moment
• No persistent storage yet
• No sample playback
• No analog front-end (op-amp / CV conditioning)
• Still a POC

Code Reference

The STM32 implementation lives here:

https://github.com/apiel/zicBox/tree/main/mcu/stm32

Conclusion

This STM32H7 port demonstrates that zicBox can run efficiently on a microcontroller while maintaining real-time audio performance.

While still a proof of concept, it provides a strong foundation for:

• A standalone embedded drum machine
• A Eurorack-compatible drum module
• A hybrid synth + sampler platform

Further work will focus on storage, sample playback, analog I/O, and expanding the synthesis engine.