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)