STM Module

STM32_MOD_2

Firmware for a small STM32F1-based audio board: either a LUT-driven oscillator into the onboard DAC, or a short effects chain on whatever comes in on the ADC. The Cube/HAL setup is real; mixer, filter, ADSR, and sampler are mostly placeholders for now (see Code layout).

MCU: STM32F103RCT6
IDE: STM32CubeIDE (GCC).

Requirements

• STM32CubeIDE (or IAR + pack for F1)
• ST firmware package STM32Cube FW_F1 V1.8.6 (matches STM32_MOD_2.ioc)

Build and flash

1. Open STM32_MOD_2.ioc or import the project from this repo in CubeIDE.
2. Build the Debug configuration (output under Debug/).
3. Flash/debug with your ST-Link (or whatever probe you use in the launch config).

Regenerating code from the .ioc is fine; user sections in main.c and friends are preserved by Cube’s USER CODE blocks.

Audio modes

Flip these in Core/Src/main.c before you build:

• ACTIVE_AUDIO_MODE — SYNTH or EFFECTS (passed into init_stm32()).
• ACTIVE_EFFECT_MODE — EFFECT_BYPASS, EFFECT_MOVING_AVG, or EFFECT_BIT_CRUSHER (Core/Inc/effects.h).
• ACTIVE_MOVING_AVG_TAPS — tap count for the moving average (capped in effects.c).

SYNTH: TIM8 triggers DAC channel 2 via DMA. Half- and full-transfer callbacks call render_audio_block(), which fills the DAC buffer from the oscillator (Core/Src/stm32_synth.c, Core/Src/oscillator.c). Waveforms are sine, square, triangle, saw, or noise (Core/Inc/oscillator.h). Right now the main loop runs marry_had_a_little_lamb() as a demo when in this mode; other tests (UART, frequency sweep, seven-seg) are commented out in the same file.

EFFECTS: ADC1 is also triggered off TIM8 TRGO, with DMA into audio_buffer_adc. ADC callbacks copy each half into audio_buffer_sig_path. DAC callbacks wait until the matching adc_half_ready[] flag is set, then run effects_process_sample() so output stays aligned with fresh input. Underrun/overrun counters on struct synth are there for debugging.

Sample rate: System clock is 24 MHz (HSI + PLL in SystemClock_Config). TIM8 is set in the IOC to prescaler 3 and period 124, which works out to about 48 kHz for the DAC/ADC trigger rate. Audio buffers are 256 samples (AUDIO_BUFFER_SIZE in Core/Inc/stm32_synth.h).

Front-panel I/O

Pin names live in Core/Inc/main.h: two buttons, a pot, an LED, SPI1 to a shift-register style display, plus digit select lines for a two-digit seven-segment display. Core/Src/seven_seg.c is refreshed from HAL_TIM_PeriodElapsedCallback() on TIM2 in main.c.

Code layout

Not wired into the synth audio path yet: struct synth already holds mixer, filter, and ADSR, and mixer.c implements a simple average of sources, but render_audio_block() only comments those stages—no calls. filter.c, adsr.c, and sampler.c are empty or stub implementations.

Hardware and diagrams

KiCad lives under Hardware/. The project file is Hardware/STM_Module.kicad_pro; schematics include e.g. Hardware/STM32.kicad_sch and Hardware/power.kicad_sch.

Block diagrams in the repo root: signal_path_diagram.drawio, stm32_structure.drawio.

License

ST’s HAL/CMSIS drop in with their usual LICENSE.txt under Drivers/—nothing special added here.