stm32/boards/STM32H747I_DISCO: Add board README with Ethernet limitation note.

Documents board features, pin configuration, and important Ethernet
hardware limitation due to ETH_MDC/SAI4_D1 pin conflict requiring
board modification. Includes build, flash, and testing instructions.

Signed-off-by: Andrew Leech <[email protected]>

Author: pi-anl

ports/stm32/boards/STM32H747I_DISCO/README.md

@@ -0,0 +1,102 @@
+# STM32H747I-DISCO Board
+
+STMicroelectronics STM32H747I-DISCO development board with STM32H747XI dual-core MCU.
+
+## Features
+
+- STM32H747XIH6 microcontroller
+  - Arm Cortex-M7 @ 480 MHz + Cortex-M4 @ 240 MHz
+  - 2 MB Flash, 1 MB RAM
+  - 32 MB external SDRAM
+- Connectivity
+  - USB High-Speed via ULPI PHY (USB3320)
+  - USB Full-Speed
+  - Ethernet RMII (LAN8742A PHY) - **requires hardware modification**
+  - microSD card slot (8-bit SDMMC1)
+- Display
+  - 4" capacitive touchscreen LCD (480×272)
+- Audio
+  - WM8994 codec with line in/out, headphone, speaker, microphone
+  - 2x digital MEMS microphones
+- Other peripherals
+  - 2× user LEDs
+  - 1× user button + reset button
+  - Arduino Uno V3 expansion connector
+  - PMOD connector
+  - Onboard ST-LINK/V3
+
+## Pin Configuration
+
+Default pin assignments:
+
+- UART1: PA9 (TX), PA10 (RX) - Connected to ST-LINK VCP
+- USB_HS: ULPI interface on PA3, PA5, PB0, PB1, PB5, PB10-13, PC0, PH4, PI11
+- I2C4: PD12 (SCL), PD13 (SDA) - WM8994 audio codec
+- SPI5: PF7 (SCK), PF8 (MISO), PF9 (MOSI), PF6 (CS)
+- UART8: PJ8 (TX), PJ9 (RX)
+- SD Card: 8-bit SDMMC1 interface on PC6-12, PB8-9, PD2
+
+## Ethernet Hardware Limitation
+
+**Important:** The Ethernet interface is not functional with the default board configuration due to a pin conflict between ETH_MDC (PC1) and SAI4_D1 (digital MEMS microphone). A hardware modification is required to disconnect the MEMS microphone from PC1 to enable Ethernet functionality. Refer to the STM32H747I-DISCO user manual (UM2411) for details on the required modification.
+
+## Building Firmware
+
+```bash
+cd ports/stm32
+make BOARD=STM32H747I_DISCO
+```
+
+## Flashing Firmware
+
+Using STM32CubeProgrammer (recommended):
+```bash
+STM32_Programmer_CLI -c port=SWD mode=UR -w build-STM32H747I_DISCO/firmware.elf -v -rst
+```
+
+Using st-flash:
+```bash
+st-flash write build-STM32H747I_DISCO/firmware.bin 0x08000000
+```
+
+## Console Access
+
+The board provides two independent console options:
+
+1. **ST-LINK V3 UART** (recommended):
+   - Device: /dev/ttyACM* (Linux), COM* (Windows)
+   - Baudrate: 115200
+   - Always available regardless of USB state
+
+2. **USB CDC serial**:
+   - Requires USB cable connected
+   - Provides MicroPython REPL
+
+Using mpremote:
+```bash
+mpremote connect /dev/ttyACM5  # Adjust device as needed
+```
+
+## Testing
+
+The board includes a test suite for verifying hardware functionality:
+
+```python
+# Run automated tests
+import run_all_tests
+run_all_tests.run_automated()
+
+# Run manual tests (requires user interaction)
+run_all_tests.run_manual()
+```
+
+Test coverage:
+- I2C (WM8994 codec)
+- ADC (3 channels)
+- SPI
+- UART
+- SD card
+- Ethernet (requires hardware modification)
+- DAC
+- PWM/Timers
+- LEDs and buttons