Support for WCH CH32X035 (RISC-V)

[NoNamedCat]

This issue presents a full port of the Mozzi library for the WCH CH32X035 microcontroller (RISC-V architecture). The
port includes hardware-level implementation for audio interrupts, high-speed PWM generation, and support for the Hi-Fi
(2-pin PWM) output mode (Not tested).

Key Implementation Details

• Low-Level Hardware Access: Since the CH32 Arduino core lacks a standard HardwareTimer class, this port uses the WCH
  Standard Peripheral Library (SPL) to directly configure registers for maximum performance.
• Timers:
  • TIM1: Configured as the master audio interrupt timer (defaulting to 16,384Hz).
  • TIM3: Configured for high-speed PWM generation (~187.5 kHz carrier frequency).
• Output Modes:
  • Standard PWM: Output on pin PA6 (TIM3_CH1).
  • Hi-Fi Mode: Dual-pin output on PA6 (High Byte) and PA7 (Low Byte) (Not tested).
• Compiler Compatibility: RISC-V GCC is stricter than AVR/ARM regarding narrowing conversion. I added a #pragma GCC
  diagnostic ignored "-Wnarrowing" specifically inside the CH32 implementation file to allow legacy Mozzi tables
  (declared as int8_t but containing values > 127) to compile without modifying the original table files.

FixMath Dependency Fixes
During the porting process, I identified and fixed broken dependencies related to the new FixMath library requirement
in Mozzi 2.0+. Several headers (Oscil.h, AudioOutput.h, etc.) were attempting to include <FixMath.h> which was missing
or failing. I updated mozzi_fixmath.h to act as a proper wrapper for the external FixMath. **

(Don't know if I'm doing good with this)**.

Files Included in the Patch

1. New: internal/MozziGuts_impl_CH32.hpp (Core logic).
2. New: internal/config_checks_CH32.h (Hardware-specific defaults).
3. Modified: hardware_defines.h (Architecture detection).
4. Modified: internal/MozziGuts.hpp & internal/config_checks_generic.h (Routing).
5. Modified: AudioOutput.h, Line.h, MetaOscil.h, mozzi_midi.h, Oscil.h, mozzi_fixmath.h (FixMath dependency
   corrections)(Don't know if I'm doing good with this).

How to Test

1. Install the openwch/arduino_core_ch32 core.
2. Install the FixMath library.
3. Install the Mozzi library.
4. Apply the attached files from the ZIP.
5. Define #define MOZZI_AUDIO_MODE MOZZI_OUTPUT_2PIN_PWM for Hi-Fi mode (Not tested) or use default for standard output on PA6.

I am attaching a ZIP file with all the modified/new files. I hope this contribution is useful for the community and
can be integrated into the main branch.

Mozzi_CH32_Port.zip

[tomcombriat]

Hello,
Thanks for this, it is always nice to have Mozzi ported on new platforms!

One question: why not submitting this as a PullRequest instead of as an Issue? This would be easier for us to have a look at the changes before merging.

For FixMath, I am a bit surprised that you needed to make modifications to make FixMath work with Mozzi: normally more or less everything should be already working without modifying Mozzi if FixMath was correctly installed. Are you using the Arduino IDE?

[NoNamedCat]

Hi @tomcombriat. I hesitated to open a PR because I had to touch several core library files to get FixMath working, and I didn't want to pollute the repo without a prior discussion.

I am using Arduino CLI, not the IDE. It seems the build system wasn't picking up the FixMath paths correctly, forcing me to edit the headers directly. Since you mentioned it should work out of the box, it might be an issue specific to how the CLI handles dependencies for this core.

[tomcombriat]

Hi @NoNamedCat ,
Sorry for the late reply.

I think in that case it would make sense to separate this into two pr/issues :

• one for the port, which should go in fairly fast after a quick check that this does not break anything
• one to fix the compilation issue with Arduino CLI, which might need a bit of investigation to understand why it works on the IDE and not on CLI.

Both are of course cool additions to Mozzi!

[NoNamedCat]

I tried replicating the same thing using the IDE instead of the CLI and encountered similar issues. Perhaps it has something to do with the Arduino core for this platform, rather than the use of the CLI. Need more investigation.