Orange Pi 4 LTS¶

You can use the Orange Pi 4 LTS, an SBC based on the Rockchip RK3399 SoC. Your board provides a 26-pin GPIO header and is supported by MainsailOS through an Armbian-based image.

Board Overview¶

GPIO Pinout¶

GPIO Chip¶

When using GPIOs with the Linux MCU in Klipper, you need to identify the correct GPIO chip and line number for each pin. The RK3399 SoC has 5 GPIO banks (GPIO0 through GPIO4), each exposed as a separate GPIO chip (gpiochip0 through gpiochip4) with 32 lines each, organized in groups A–D (8 pins each).

Header Pin Mapping¶

The following table lists all GPIO pins on the 26-pin header with their Klipper pin references:

Calculating GPIO Line Numbers¶

The RK3399 uses the naming format GPIOx_Yn, where x is the bank (0–4), Y is the group letter (A–D), and n is the pin number (0–7). To calculate the GPIO line number:

GPIO line = group × 8 + pin

Where group values are: A=0, B=1, C=2, D=3. The bank number determines the GPIO chip (gpiochipN).

Example: GPIO1_B2 → chip = gpiochip1, line = 1 × 8 + 2 = 10 → Klipper pin: host:gpiochip1/gpio10

UART¶

UART is not enabled by default in MainsailOS for the Orange Pi 4 LTS because UART4 shares its pins (GPIO1_A7 and GPIO1_B0) with SPI1, which is pre-configured for accelerometer use. To use UART4 for serial MCU communication, you need to disable SPI1 first.

Edit /boot/armbianEnv.txt:

sudo nano /boot/armbianEnv.txt

Replace the SPI overlay with the UART4 overlay and remove the SPI parameters:

# Change this:
overlays=spi-spidev
param_spidev_spi_bus=1

# To this:
overlays=uart4
#param_spidev_spi_bus=1

Then reboot. The UART device will be available at /dev/ttyS4.

SPI¶

SPI1 is enabled by default in MainsailOS. The spi-spidev overlay and spi-dev kernel module are pre-configured for use with accelerometers for Input Shaper.

The SPI device is available at /dev/spidev1.0.

Example Klipper configuration for an ADXL345 accelerometer:

[adxl345]
cs_pin: host:gpiochip1/gpio10
spi_bus: spidev1.0

I2C¶

I2C3 is available on the GPIO header at /dev/i2c-3 without any additional overlay configuration.

In your Klipper configuration, use i2c_bus: i2c.3:

[temperature_sensor example]
sensor_type: HTU21D
i2c_mcu: host
i2c_bus: i2c.3

Further Resources¶

• Orange Pi 4 LTS — Official Page
• Armbian Documentation
• Klipper RPi Microcontroller — Klipper Linux MCU guide