u8g2

U8g2 is a monochrome graphics library for embedded devices supporting a wide range of OLED and LCD controllers (e.g., SSD1306, SH1106, ST7920, etc.). The project provides two distinct libraries depending on your memory and feature requirements:

• U8g2: A full graphics library. It includes procedures for drawing lines, boxes, and circles, and supports a vast array of fonts with varying heights. Note that it requires microcontroller memory to maintain a buffer for rendering the display.
• U8x8: A text-only character device library. It is designed for extremely low-memory environments as it writes directly to the display without requiring a microcontroller buffer. It only supports fonts that fit within an 8x8 pixel grid.

When working with SSD13xx displays, observe the following timing constraints to ensure stable operation:

• Power-on delay: SSD1306 and SSD1306b require a "stable" delay. SSD1317 and SSD1320 require 20ms. SSD1322, SSD1325, SSD1326, and SSD1327 require a "stable" delay.
• Init to Data delay: Most controllers (SSD1306, SSD1306b, SSD1309, SSD1312, SSD1317, SSD1320, SSD1322, SSD1325, SSD1326, SSD1327) require a 100ms delay after initialization before data can be sent.

Use this build method for legacy kernels that do not support the GPIO character device.

cd ~/u8g2/sys/arm-linux
make clean
make CC=gcc CXX=g++

You can set up U8g2 on the RT-Thread operating system using either a GUI-based approach or a terminal-based approach depending on your preferred environment:

• Windows (GUI): Use RT-Thread Studio. A video tutorial is available on YouTube to guide you through the process.
• Ubuntu (Terminal): Use RT-Thread ENV tools. A terminal-based tutorial is available via asciinema.

Note: RT-Thread offers both a Standard version for resource-rich IoT devices (manageable via online software packages) and a Nano version for resource-constrained MCUs (requiring as little as 3 KB Flash and 1.2 KB RAM).

Use this build method for better performance and stability on modern kernels. It utilizes the c-periphery userspace library via the GPIO character device.

cd ~/u8g2/sys/arm-linux
make clean
make CPPFLAGS=-DPERIPHERY_GPIO_CDEV_SUPPORT=1 CC=gcc CXX=g++

When implementing the DMA SPI configuration for the STM32L031, use the following GPIO mapping for the display connections:

This guide provides the hardware wiring and performance benchmarks for using U8g2 with an STM32L031 microcontroller using DMA SPI. This configuration is optimized for high FPS (Frames Per Second) using the uc1609_slg19264_f or uc1609_slg19264_1 constructors.

GPIO Wiring Mapping

Connect the display to the STM32L031 using the following GPIO pins:

To access GPIO, I2C, and SPI devices without running as root, create a dedicated u8g2 group, add your user to it, and set permissions for the device files via /etc/rc.local.

sudo groupadd u8g2
sudo usermod -a -G u8g2 username

# Add the following to /etc/rc.local:
chown -R root:u8g2 /dev/gpiochip*
chmod -R ug+rw /dev/gpiochip*
chown -R root:u8g2 /dev/i2c*
chmod -R ug+rw /dev/i2c*
chown -R root:u8g2 /dev/spidev*
chmod -R ug+rw /dev/spidev*

Before building, you must modify the example source files to match your specific hardware configuration. Key parameters to adjust in the .c files include:

• GPIO_CHIP_NUM: The GPIO chip number (e.g., 0 for /dev/gpiochip0).
• SPI_BUS: The SPI bus number (e.g., 0x10 for /dev/spidev1.0).
• OLED_SPI_PIN_RES: The RESET pin number.
• OLED_SPI_PIN_DC: The DC pin number.

This implementation provides a reference HAL (Hardware Abstraction Layer) for integrating u8g2 with Raspberry Pi Pico-class boards using the official Raspberry Pi Pico SDK. It is intended to be used as a template that can be copied and adapted for specific projects on RP2040 or RP2350 platforms.

The implementation provides minimal HAL layers for:

• GPIO control
• Delay functions
• Communication callbacks (e.g., SPI/I2C)

This example is compatible with both the Raspberry Pi Pico (RP2040) and Raspberry Pi Pico 2 (RP2350) without modification.