Microbus

Microbus is a lightweight project created to address the need for a universal bus bridge for embedded development, accessible directly from a Linux host PC.

The core idea is simple: provide a low-cost, flexible way to access common embedded buses (such as I²C, 1-Wire, and SPI) from Linux using standard kernel device subsystems. Given the abundance of inexpensive microcontrollers, mostly ARM-based, the concept of building a universal bus bridge for just a few dollars proved both practical and promising.

The project is currently under active development, and not all planned features are fully implemented yet.

---

Project Overview

Microbus consists of two main components:

• Linux kernel module
  • Exposes embedded buses through the Linux device model (/dev/i2c-X, /dev/spi)
    • Creates custom /dev/ow-X devices for 1-Wire buses to enable raw communication with slave devices
  • Compilation and Module Usage
• Target firmware
  • Runs on a microcontroller
  • Bridges Linux bus operations to physical hardware
  • Communicates with the host via UART or USB

This architecture allows Linux applications to interact with embedded peripherals as if they were native Linux devices.

---

Supported Protocols

Protocol	Status
I²C	✅ Supported
1-Wire	✅ Supported
SPI	🚧 Planned

---

Supported Hardware

Host

• Linux-based PC (kernel module required)

Target devices

• ✅ Arduino Nano

---

Planned Hardware Support

• ESP32-based boards
• Raspberry Pi Pico / Pico 2
• Additional low-cost ARM and RISC-V MCUs

---

Communication Interfaces

• UART (primary)
• USB (planned / experimental)

---

Build and Deployment

Each firmware target and the kernel module contains its own build and deployment instructions.

Please refer to:

• kernel/ – Linux kernel module build instructions
• firmware/<target>/ - target-specific firmware build and flashing guides

---

Example Use Cases

I²C

---

• Assumptions
  • System environment
    • I2C_DEV_NO - index of the I²C bus to be used (e.g. 1)

index of the I²C bus to be used (e.g. 1)

sudo i2cdetect -y 23
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:                         -- -- -- -- -- -- -- -- 
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
40: -- -- -- -- -- -- -- -- 48 -- -- -- -- -- -- -- 
50: 50 51 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
70: -- -- -- -- -- -- -- --

EEPROM Access (AT24C04)

Access external EEPROM devices over I²C directly from Linux userspace.

sudo modprobe at24

# Register the E2PROM device on the selected I²C bus
sudo bash -c "echo 24c04 0x50 > /sys/bus/i2c/devices/i2c-${I2C_DEV_NO}/new_device"

# Dump E2PROM contents
sudo cat /sys/bus/i2c/drivers/at24/${I2C_DEV_NO}$-0050/eeprom | tee eeprom-read.bin | hexdump -C

ADC Access (ADS1115)

Read analog values from remote ADCs using standard Linux interfaces.

# Load the ADC driver
sudo modprobe ti-ads1015

# Register the ADC device on the selected I²C bus
sudo bash -c "echo ads1115 0x48 > /sys/bus/i2c/devices/i2c-${I2C_DEV_NO}/new_device"

# Configure input scaling (±6.144 V range)
sudo bash -c "echo 0.187500000 > /sys/bus/iio/devices/iio\:device0/in_voltage0_scale"

# Read the raw ADC value
cat /sys/bus/iio/devices/iio\:device0/in_voltage0_raw
25473

# Convert the raw value to millivolts
echo "$(cat /sys/bus/iio/devices/iio:device0/in_voltage0_raw) * $(cat /sys/bus/iio/devices/iio:device0/in_voltage0_scale)" | bc -l
4776.937500000

RTC Clock (DS1307)

Expose external RTC devices as Linux clock sources.

sudo modprobe rtc-ds1307

sudo bash -c "echo ds1307 0x68 > /sys/bus/i2c/devices/i2c-${I2C_DEV_NO}/new_device"

sudo hwclock -r
sudo hwclock -w

Light Sensor (TSL2561)

# Load the kernel driver (tsl2563 supports TSL2561)
sudo modprobe tsl2563

# Register the sensor on the selected I²C bus
sudo bash -c "echo tsl2561 0x39 > /sys/bus/i2c/devices/i2c-${I2C_DEV_NO}/new_device"

# Read illuminance value (lux)
cat /sys/bus/iio/devices/iio\:device0/in_illuminance0_input 

1Wire

---

Assumptions

• Kernel modules
  • wire module is loaded

    sudo modprobe wire

  • w1-therm module is loaded (1-wire thermal sensors)

    sudo modprobe w1-therm

Listing master devices

ls  /sys/bus/w1/devices/

28-112233445500  28-112233445501  28-112233445502  w1_bus_master1

---

Project Status

⚠️ Work in progress

• APIs may change
• Not all protocols are implemented
• Stability is not yet guaranteed

Contributions, testing, and feedback are welcome.

---

License

The project uses a mixed licensing model:

• Linux kernel module: GPL-2.0
• Shared and userspace components: MIT, depending on the file

See individual source files for SPDX license identifiers.