hardware

# Hardware (I2C / SPI) Use the `i2c` and `spi` tools to interact with sensors, displays, and other peripherals connected to the board. ## Quick Start ``` # 1. Find available buses i2c detect # 2. Scan for connected devices i2c scan (bus: "1") # 3. Read from a sensor (e.g. AHT20 temperature/humidity) i2c read (bus: "1", address: 0x38, register: 0xAC, length: 6) # 4. SPI devices spi list spi read (device: "2.0", length: 4) ``` ## Before You Start — Pinmux Setup Most I2C/SPI pins are shared with WiFi on Sipeed boards. You must configure pinmux before use. See `references/board-pinout.md` for board-specific commands. **Common steps:** 1. Stop WiFi if using shared pins: `/etc/init.d/S30wifi stop` 2. Load i2c-dev module: `modprobe i2c-dev` 3. Configure pinmux with `devmem` (board-specific) 4. Verify with `i2c detect` and `i2c scan` ## Safety - **Write operations** require `confirm: true` — always confirm with the user first - I2C addresses are validated to 7-bit range (0x03-0x77) - SPI modes are validated (0-3 only) - Maximum per-transaction: 256 bytes (I2C), 4096 bytes (SPI) ## Common Devices See `references/common-devices.md` for register maps and usage of popular sensors: AHT20, BME280, SSD1306 OLED, MPU6050 IMU, DS3231 RTC, INA219 power monitor, PCA9685 PWM, and more. ## Troubleshooting | Problem | Solution | |---------|----------| | No I2C buses found | `modprobe i2c-dev` and check device tree | | Permission denied | Run as root or add user to `i2c` group | | No devices on scan | Check wiring, pull-up resistors (4.7k typical), and pinmux | | Bus number changed | I2C adapter numbers can shift between boots; use `i2c detect` to find current assignment | | WiFi stopped working | I2C-1/SPI-2 share pins with WiFi SDIO; can't use both simultaneously | | `devmem` not found | Download separately or use `busybox devmem` | | SPI transfer returns all zeros | Check MISO wiring and device power | | SPI transfer returns all 0xFF | Device not responding; check CS pin and clock polarity (mode) |