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Gamma Hardware Pinout & Peripheral Reference

This skill documents the complete hardware pinout, electrical characteristics, and peripheral mappings for the this.is.NOISE Gamma Mini Synth, powered by an embedded Electro-Smith Daisy Seed 2 DFM (ARM Cortex-M7 @ 480 MHz, STM32H750IBK6, PCM3060 stereo audio codec).

A ready-to-use C++ header containing these definitions is available at: resources/gamma_pins.h

1. System Overview

Parameter Specification
Microcontroller STMicroelectronics STM32H750IBK6 (ARM Cortex-M7 @ 480 MHz)
Carrier Board Electro-Smith Daisy Seed 2 DFM
Audio Codec Texas Instruments PCM3060 24-bit stereo codec via SAI1 @ 48 kHz
Display 1.3" OLED (SSD1306 controller, 128x64 monochrome) via I2C1 @ 0x3D
Bootloader Electro-Smith Daisy Bootloader in internal flash (0x08000000)
Application Memory Binaries flashed to QSPI flash (0x90040000), loaded to AXI SRAM (0x24000000, APP_TYPE = BOOT_SRAM)
USB Interface External USB port: USB_OTG_HS in Full Speed mode on seed::D29/seed::D30 (PB14/PB15). Use UsbHandle::FS_EXTERNAL / Logger<LOGGER_EXTERNAL> — not hw.StartLog()

2. Master Pinout Table

Peripheral Label Daisy Seed Pin STM32 Pin Function / Channel Electrical Config Polarity / Logic Verification Status
OLED Display SCL seed::D11 PB8 I2C1_SCL Alternate Function 4 Open-drain w/ pullup Verified on Hardware
OLED Display SDA seed::D12 PB9 I2C1_SDA Alternate Function 4 Open-drain w/ pullup Verified on Hardware
Potentiometer Knob 1 / K0 (Chord Vol) seed::D18 PA7 ADC1_INP7 (A3) Analog Input Inverted: 1.0 - raw Verified on Hardware
Potentiometer Knob 2 / K1 (Chord Filter) seed::D17 PB1 ADC1_INP5 (A2) Analog Input Inverted: 1.0 - raw Verified on Hardware
Potentiometer Knob 3 / K2 (Notes Vol) seed::D19 PA6 ADC1_INP3 (A4) Analog Input Inverted: 1.0 - raw Verified on Hardware
Potentiometer Knob 4 / K3 (Notes Filter) seed::D20 PC1 ADC1_INP11 (A5) Analog Input Inverted: 1.0 - raw Verified on Hardware
Joystick Left LX (Left-Right) seed::D22 PA5 ADC1_INP19 (A7) Analog Input Normal: Left=0%, Right=100% Verified on Hardware
Joystick Left LY (Down-Up) seed::D21 PC4 ADC1_INP4 (A6) Analog Input Inverted: Down=0%, Up=100% Verified on Hardware
Joystick Right RX (Left-Right) seed::D24 PA1 ADC1_INP17 (A9) Analog Input Inverted: Left=0%, Right=100% Verified on Hardware
Joystick Right RY (Down-Up) seed::D23 PA4 ADC1_INP18 (A8) Analog Input Inverted: Down=0%, Up=100% Verified on Hardware
Auxiliary ADC AUX (Battery/Sens) seed::D31 PC2 ADC1_INP12 (A12) Analog Input Direct voltage readout Confirmed Disassembly
Note Key N1 Keypad Left Top 1 seed::D1 PC11 GPIO In Internal Pull-up Active LOW (Pressed = 0) Verified on Hardware
Note Key N2 Keypad Left Top 2 seed::D2 PC10 GPIO In Internal Pull-up Active LOW (Pressed = 0) Verified on Hardware
Note Key N3 Keypad Left Top 3 seed::D3 PC9 GPIO In Internal Pull-up Active LOW (Pressed = 0) Verified on Hardware
Note Key N4 Keypad Left Top 4 seed::D4 PC8 GPIO In Internal Pull-up Active LOW (Pressed = 0) Verified on Hardware
Note Key N5 Keypad Left Bot 1 seed::D5 PD2 GPIO In Internal Pull-up Active LOW (Pressed = 0) Verified on Hardware
Note Key N6 Keypad Left Bot 2 seed::D6 PC12 GPIO In Internal Pull-up Active LOW (Pressed = 0) Verified on Hardware
Note Key N7 Keypad Left Bot 3 seed::D7 PG10 GPIO In Internal Pull-up Active LOW (Pressed = 0) Verified on Hardware
Chord Key C1 Keypad Right Top 1 seed::D8 PG11 GPIO In Internal Pull-up Active LOW (Pressed = 0) Verified on Hardware
Chord Key C2 Keypad Right Top 2 seed::D9 PB4 GPIO In Internal Pull-up Active LOW (Pressed = 0) Verified on Hardware
Chord Key C3 Keypad Right Top 3 seed::D10 PB5 GPIO In Internal Pull-up Active LOW (Pressed = 0) Verified on Hardware
Chord Key C4 Keypad Right Top 4 seed::D13 PB6 GPIO In Internal Pull-up Active LOW (Pressed = 0) Verified on Hardware
Chord Key C5 Keypad Right Bot 1 seed::D14 PB7 GPIO In Internal Pull-up Active LOW (Pressed = 0) Verified on Hardware
Chord Key C6 Keypad Right Bot 2 seed::D26 PD11 GPIO In Internal Pull-up Active LOW (Pressed = 0) Verified on Hardware
Chord Key C7 Keypad Right Bot 3 seed::D27 PG9 GPIO In Internal Pull-up Active LOW (Pressed = 0) Verified on Hardware
Rotary Encoder Phase A seed::D15 PC0 GPIO In Internal Pull-up Quadrature Gray Code Verified on Hardware
Rotary Encoder Phase B seed::D16 PA3 GPIO In Internal Pull-up Quadrature Gray Code Verified on Hardware
Rotary Encoder Push Button seed::D28 PA2 GPIO In Internal Pull-up Active LOW (Pressed = 0) Verified on Hardware
Speaker Amp En Speaker Enable/Mute seed::D32 (seed::A13) PC3 GPIO Out Output Push-Pull Active HIGH (1=On, 0=Muted) Verified on Hardware
Power Fault Sense Battery Low / Power Fault seed::D0 PB12 GPIO In Internal Pull-up Active LOW ("Charge Me!") Confirmed Disassembly
Audio Out Stereo DAC Out Internal Multiple SAI1 PCM3060 Codec 48 kHz / 24-bit Stereo Internal Daisy routing
MIDI USB-C MIDI (Class Compliant) seed::D29/seed::D30 PB14/PB15 USB_OTG_HS (FS mode) Full Speed USB Device MidiUsbHandler with MidiUsbTransport::Config::EXTERNAL (no 3.5mm MIDI) Not yet implemented
USB-C D- / D+ / Power seed::D29/seed::D30 PB14/PB15 USB_OTG_HS (FS mode) Full Speed Device UsbHandle::FS_EXTERNAL Verified on Hardware (CDC)

3. OLED Display Interface

  • Controller: Solomon Systech SSD1306 (128x64 monochrome)
  • Bus Peripheral: I2C1 (0x40005400)
  • Pins:
  • SCL: seed::D11 (PB8, GPIO_AF4_I2C1)
  • SDA: seed::D12 (PB9, GPIO_AF4_I2C1)
  • 7-bit I2C Address: 0x3D (0x7A 8-bit write address)
  • Clock Speed: Up to I2C_1MHZ (Fast Mode Plus).
  • Hardware & Driver Traps:
  • Persistent GDDRAM: The display panel retains its internal image as long as 3.3V power is applied. An uninitialized or hung microcontroller leaves the previous image on screen.
  • Bus Reset: After soft-resetting or branching from the bootloader, ensure __HAL_RCC_I2C1_FORCE_RESET() and __HAL_RCC_I2C1_RELEASE_RESET() are invoked before initializing I2CHandle to clear any stalled bus transitions.
I2CHandle::Config i2c_config;
i2c_config.periph         = I2CHandle::Config::Peripheral::I2C_1;
i2c_config.speed          = I2CHandle::Config::Speed::I2C_1MHZ;
i2c_config.pin_config.scl = seed::D11; // PB8
i2c_config.pin_config.sda = seed::D12; // PB9

OledDisplay<SSD130xI2c128x64Driver>::Config oled_config;
oled_config.driver_config.transport_config.i2c_address = 0x3D;
oled_config.driver_config.transport_config.i2c_config  = i2c_config;

4. Analog Inputs (ADC1: Knobs & Joysticks)

All 8 user analog controls and the auxiliary channel route into the STM32H750's ADC1 converter.

A. 4 Rotary Potentiometers (Knobs Across Top Panel)

Physical order from left to right:

  1. Knob 0 (Chord Vol): seed::D18 (PA7 / ADC1_INP7 / A3)
  2. Knob 1 (Chord Filter): seed::D17 (PB1 / ADC1_INP5 / A2)
  3. Knob 2 (Notes Vol): seed::D19 (PA6 / ADC1_INP3 / A4)

  4. Knob 3 (Notes Filter): seed::D20 (PC1 / ADC1_INP11 / A5)

  5. Electrical Polarity: Potentiometer wipers sweep from 3.3V (counter-clockwise) to 0V (clockwise).

  6. Software Inversion: Must be inverted in software (value = 1.0f - raw) so that 0.0f = full CCW and 1.0f = full CW.
  7. Filtering: Official firmware applies a heavy IIR smoothing filter (coefficient \(\approx 0.002\)) for jitter-free potentiometer reading.

B. 2 Dual-Axis Joysticks (4 Analog Axes)

  1. Left Stick X (LX): seed::D22 (PA5 / ADC1_INP19 / A7)
  2. Polarity: Standard (raw). Left = 0.0f, Right = 1.0f.
  3. Left Stick Y (LY): seed::D21 (PC4 / ADC1_INP4 / A6)
  4. Polarity: Inverted (1.0f - raw). Down = 0.0f, Up = 1.0f.
  5. Right Stick X (RX): seed::D24 (PA1 / ADC1_INP17 / A9)
  6. Polarity: Inverted (1.0f - raw). Left = 0.0f, Right = 1.0f.
  7. Right Stick Y (RY): seed::D23 (PA4 / ADC1_INP18 / A8)
  8. Polarity: Inverted (1.0f - raw). Down = 0.0f, Up = 1.0f.

[!NOTE] Hardware Polarity Rationale: Both joystick gimbals share identical Y-axis orientation relative to VCC/GND. However, the X-axis on the Right stick is electrically reversed relative to the Left stick. This is standard PCB design practice on dual-joystick layouts: reversing 3.3V and GND on one potentiometer simplifies PCB trace fanout and ground plane continuity without adding via hops.

  • Filtering: Official firmware applies a fast, responsive IIR filter (coefficient \(\approx 0.05\)) to provide low-latency modulation.

C. Auxiliary / Battery ADC

  • Aux Channel: seed::D31 (PC2 / ADC1_INP12)
  • Used for battery level monitoring or internal board power diagnostics.

5. Digital Keypad (14 Low-Profile Tactile Switches)

The Gamma synthesizer has 14 tactile keys arranged into two distinct physical grids: 7 Note keys on the left and 7 Chord keys on the right.

Each switch connects directly to a dedicated MCU GPIO with internal pull-up (INPUT_PULLUP).

  • Unpressed: Pin reads HIGH (1)
  • Pressed: Pin reads LOW (0)

Left Keypad: 7 Note Keys (N1–N7)

  [ N1 ]   [ N2 ]   [ N3 ]   [ N4 ]     <-- Top Row
  [ N5 ]   [ N6 ]   [ N7 ]              <-- Bottom Row
  • Top Row (Left to Right):
  • N1: seed::D1 (PC11)
  • N2: seed::D2 (PC10)
  • N3: seed::D3 (PC9)
  • N4: seed::D4 (PC8)
  • Bottom Row (Left to Right):
  • N5: seed::D5 (PD2)
  • N6: seed::D6 (PC12)
  • N7: seed::D7 (PG10)

Right Keypad: 7 Chord Keys (C1–C7)

  [ C1 ]   [ C2 ]   [ C3 ]   [ C4 ]     <-- Top Row
  [ C5 ]   [ C6 ]   [ C7 ]              <-- Bottom Row
  • Top Row (Left to Right):
  • C1: seed::D8 (PG11)
  • C2: seed::D9 (PB4)
  • C3: seed::D10 (PB5)
  • C4: seed::D13 (PB6)
  • Bottom Row (Left to Right):
  • C5: seed::D14 (PB7)
  • C6: seed::D26 (PD11)
  • C7: seed::D27 (PG9)

6. Rotary Encoder & Integrated Push Switch

The rotary dial on the front panel is connected via a 4-wire harness:

  • GND: Shared ground wire
  • Phase A: seed::D15 (PC0, input pull-up)
  • Phase B: seed::D16 (PA3, input pull-up)
  • Push Switch: seed::D28 (PA2, active-low input pull-up; reads LOW when clicked)

Quadrature Timing & Interrupt Requirements

  • Detent Resolution: Standard mechanical encoder generating 4 Gray code transitions per detent click.
  • Polling Hazard: Updating the 128x64 SSD1306 display via I2C blocks the CPU for \(\approx 23\text{ ms}\) per frame. Polling the encoder in the main while(1) loop will reliably drop clicks during display refreshes.
  • Solution: Sample the encoder in a high-frequency, jitter-free interrupt callback:
  • Either an audio DMA callback (AudioCallback @ 48 kHz / block size), or
  • A dedicated hardware timer (e.g., TIM5 @ 1 kHz).

7. Speaker Amplifier Enable & System Power GPIOs

  • seed::D32 / PC3 (Speaker Amplifier Enable / Mute):
  • Defined in libDaisy as seed::D32 (and alias seed::A13 on Daisy Seed 2 DFM).
  • Configured as a GPIO Output push-pull.
  • Controls the shutdown/enable pin of the on-board Class-D speaker amplifier driving the internal case speakers.
  • Polarity: Active HIGH.
    • 0 (LOW): Speaker amplifier in shutdown / muted (SPK OFF).
    • 1 (HIGH): Speaker amplifier enabled (SPK ON).
  • Anti-Pop Initialization Sequence: Hold PC3 LOW (0) during boot and peripheral setup. After starting the audio engine (hw.StartAudio()), delay \(\approx 60\text{ ms}\) to allow DAC bias voltages to stabilize before driving PC3 HIGH (1).
  • Standard UI Interaction: Short-pressing the rotary encoder push switch (seed::D28 / PA2) toggles PC3 state (g_speaker_enabled), while the OLED header displays the current state (SPK vs MUT).
  • seed::D0 (PB12 - Power Fault / Battery Low Monitor):
  • Configured as a GPIO Input with internal pull-up.
  • Monitored by the main loop: when pulled LOW (0), factory firmware displays "Charge Me!" and halts audio output.

8. USB-C Interface & USB MIDI

  • Port: The USB-C connector is wired to the Seed's external USB pins: seed::D29 (PB14, D-) and seed::D30 (PB15, D+), driven by USB_OTG_HS in Full Speed (12 Mbps) mode. The internal PA11/PA12 (USB_OTG_FS) port is not connected to the jack.
  • Hardware evidence: with CDC on FS_INTERNAL, USB_OTG_FS was powered, B-valid overridden and D+ pulled up (DCTL.SDIS = 0), yet DSTS frame number stayed 0 (no SOF from the host) and macOS never enumerated it. Switching to FS_EXTERNAL enumerates immediately as Daisy Seed External (0483:5740).
  • USB CDC Serial (diagnostics): DaisySeed::StartLog() / hw.PrintLine() are hard-wired to the internal port and will never appear on the host. Always initialize CDC on UsbHandle::FS_EXTERNAL.
  • CRITICAL: The Logger<LOGGER_EXTERNAL> Deadlock Hazard:
  • daisy::Logger<LOGGER_EXTERNAL> starts in non-blocking mode (LOGGER_SYNC_OUT). However, as soon as it successfully transmits 2 packets to a host terminal, it permanently switches to synchronous blocking mode (LOGGER_SYNC_IN).
  • In blocking mode, TransmitSync() runs while(false == impl_.Transmit) {} with no timeout.
  • When a host terminal or script closes the port or stops reading, CDC_Transmit_HS() returns USBD_BUSY forever. Any subsequent log call in the main loop (e.g., when a key is pressed) enters an infinite loop, freezing the main loop.
  • Because the main loop freezes while the audio DMA interrupt keeps running, the synth locks up with a note stuck playing continuously!
  • Deadlock-Immune Non-Blocking Logger Pattern: Replace Logger<LOGGER_EXTERNAL> with a custom timeout-guarded logger using hw.usb_handle.TransmitExternal():
struct UsbLog
{
    static void StartLog(bool wait_for_pc = false)
    {
        (void)wait_for_pc;
        hw.usb_handle.Init(UsbHandle::FS_EXTERNAL);
    }

    static void PrintLine(const char* format, ...)
    {
        va_list args;
        va_start(args, format);
        LogInternal(true, format, args);
        va_end(args);
    }

private:
    static void LogInternal(bool newline, const char* format, va_list args)
    {
        static constexpr size_t kNumBufs = 4;
        static constexpr size_t kBufSize = 256;
        static char   s_tx_bufs[kNumBufs][kBufSize];
        static size_t s_cur_buf         = 0;
        static uint32_t s_last_timeout_ms = 0;

        char* buf = s_tx_bufs[s_cur_buf];
        int   len = vsnprintf(buf, kBufSize - 3, format, args);
        if(len <= 0) return;
        if(len > (int)(kBufSize - 3)) len = kBufSize - 3;
        if(newline) { buf[len++] = '\r'; buf[len++] = '\n'; buf[len] = '\0'; }

        uint32_t now_ms = System::GetNow();
        // Fast-fail bypass if recently timed out to avoid stacking delays
        if(s_last_timeout_ms > 0 && (now_ms - s_last_timeout_ms < 200))
        {
            if(hw.usb_handle.TransmitExternal((uint8_t*)buf, len) == UsbHandle::Result::OK)
            {
                s_last_timeout_ms = 0;
                s_cur_buf         = (s_cur_buf + 1) % kNumBufs;
            }
            return;
        }

        // Allow up to 500 us for an in-flight packet to complete
        uint32_t start_us = System::GetUs();
        while(hw.usb_handle.TransmitExternal((uint8_t*)buf, len) != UsbHandle::Result::OK)
        {
            if(System::GetUs() - start_us >= 500)
            {
                s_last_timeout_ms = System::GetNow();
                return; // Drop message safely; NEVER hang the synth!
            }
        }
        s_last_timeout_ms = 0;
        s_cur_buf         = (s_cur_buf + 1) % kNumBufs;
    }
};
  • Never print from the USB receive callback: UsbRxCallback runs in the USB interrupt. Queue received bytes into a ring buffer and process commands in the main loop (see firmware/phase5_audio/main.cpp). Support the 'b' command for automated flashing by calling System::ResetToBootloader(System::DAISY_INFINITE_TIMEOUT). Do not call it with no argument: that defaults to the STM32 ROM bootloader, which cannot program the QSPI app slot at 0x90040000.
  • MIDI Implementation:
  • The Gamma Mini Synth has no hardware 3.5mm TRS MIDI port. All MIDI communication is handled over the USB-C connector as a class-compliant USB MIDI device.
  • In libDaisy, use daisy::MidiUsbHandler with midi_cfg.transport_config.periph = daisy::MidiUsbTransport::Config::EXTERNAL. No discrete GPIO configuration is required; libDaisy configures PB14/PB15 for USB_OTG_HS.
  • VBUS sensing: Stock libDaisy already sets hpcd_USB_OTG_HS.Init.vbus_sensing_enable = DISABLE, so the external port works with unmodified libDaisy. (An earlier local patch disabling VBUS sensing on hpcd_USB_OTG_FS only affected the unconnected internal port and has been reverted.)
  • USB clock: The Gamma's Daisy Bootloader reports as v6.1+ (System::GetBootloaderVersion() = 3 = Version::v6_1), so DaisySeed::Init() performs full clock configuration, including HSI48 routed to RCC_USBCLKSOURCE_HSI48. No application-level clock setup is needed.