USB Audio Interface Design
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Created a project doc
Firmware Starter — U17 STM32G474RET6
This file is the bring-up baseline for U17 (STM32G474RET6, LQFP-64). Pin mappings below were read from the live schematic. The example targe...
Completed the MCU/UI control block with U17 STM32G474RET6, SWD programming, power/reset support, encoder, four status LEDs, and connections to PD, phantom, preamp, eFuse, and power-good signals. Focused MCU ERC and passive checks are clean.
Open items:
- New components remain unplaced on the PCB.
- Local schematic label/wire collisions need a later legibility cleanup.
Firmware setup and the complete GPIO map are in Firmware Starter — STM32G474RET6.
Suggested next steps:
- Review full schematic/ERC and resolve remaining system-level issues.
- Clean up schematic block arrangement.
- Finalize all generic passive MPNs and footprints.
- Then transition to PCB constraints and placement.
Review and clean schematic
Run full ERC
Clean schematic layout
Finalize passive BOM
Prepare PCB constraints
Refine this doc
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Firmware Starter — U17 STM32G474RET6
This file is the bring-up baseline for U17 (STM32G474RET6, LQFP-64). Pin mappings below were read from the live schematic. The example targets STM32CubeIDE / STM32CubeMX with STM32 HAL and is intended to replace the generated
Core/Src/main.c (or to be merged into CubeMX USER CODE regions).Safety: phantom power can damage non-phantom equipment. Firmware starts withPHANTOM_EN_TO_MCUlow, holds the THAT5171 in reset, and holdsPD_SNK_EN_ODlow. It does not enable phantom automatically.
1. Platform and CubeMX configuration
- MCU:
STM32G474RET6, package LQFP64. - Toolchain: current STM32CubeIDE with STM32CubeG4 HAL. PlatformIO is also viable with
framework = stm32cube, but CubeIDE is the reference because it generates the pin labels and HAL handles used below. - Debug: Serial Wire, with SWO enabled if wanted. Do not reclaim PA13, PA14, or PB3.
- Clock: the schematic has no crystal on U17 PF0/PF1 or PC14/PC15. Select HSI16 as clock source. A simple 16 MHz HSI system clock is adequate for bring-up and avoids inventing an oscillator. The generated
SystemClock_Config()may later use the PLL, but keep SPI1 at or below 10 MHz. SYS: Debug = Serial Wire (or Trace Asynchronous SW if PB3/SWO is used).I2C1: PB6 = SCL and PB7 = SDA, 100 kHz initially, 7-bit addressing. External 4.7 kΩ pull-ups R2/R1 already connect both nets to3V3_DIG. Enable analog filter. Generate handlehi2c1.SPI1: full-duplex master, PA4 software GPIO chip select, PA5 SCK, PA6 MISO, PA7 MOSI; 8-bit, MSB first, CPOL low / CPHA first edge (mode 0), software NSS. Choose a prescaler giving SCLK3V3_DIG- pin 2 SWDIO/TMS ->
MCU_SWDIO-> U17 PA13 - pin 4 SWDCLK/TCK ->
MCU_SWCLK-> U17 PA14 - pin 6 SWO/TDO ->
MCU_SWO-> U17 PB3 - pin 10
~RESET~->MCU_NRST - pins 3/5 and GNDDetect ->
GND
Use an ST-LINK with a keyed 10-pin Cortex cable. VTref is a target reference, not a request to back-power the board.
- Open the
.iocin STM32CubeIDE, apply the configuration/labels above, and generate code. - Merge the starter source while preserving CubeMX-generated peripheral init functions.
- Build: Project -> Build Project (or
make -jin the generated Debug directory). - Power the board normally, connect ST-LINK to J6, select Debug As -> STM32 Cortex-M C/C++ Application.
- Use SWD, connect under reset if required, program, reset, and verify the red/blue/green startup indications.
- CLI alternative with STM32CubeProgrammer:
STM32_Programmer_CLI -c port=SWD mode=UR -w Debug/.elf -v -rst.
7. Bring-up checks
- Confirm U17 is powered at
3V3_DIGand J6 VTref is near 3.3 V before attaching the debugger. - At reset:
PHANTOM_EN_TO_MCUlow,PREAMP_GAIN_RST_N_TO_MCUlow,SPI_PREAMP_CS_Nhigh. - Verify I2C ACK at 7-bit
0x28; if absent, hold phantom off and inspect U1/reset/power/strap hardware. - Verify THAT5171 CHIP_ID masked by
0xFCequals0x84after reset release. - Rotate SW1 and verify TIM2 counter changes; press switch and verify active-low PA2.
- Compare PC0 raw ADC samples against measured
PHANTOM_MON_ADC_TO_MCU. Conversion to volts requires the finalized divider transfer ratio; this starter leaves the value raw rather than inventing calibration. - Do not enable phantom during initial digital bring-up.
1. Platform and CubeMX configuration
Required CubeMX user labels
2. Complete U17 pin table (live schematic)
3. Peripheral/protocol notes
STUSB4500 over I2C1
THAT5171 over SPI1
4. Cohesive `main.c` starter
GPIO initialization requirements
5. Safe startup sequence
6. Build and flash through J6 SWD
7. Bring-up checks
