BusBom Project Installation and Usage Manual

1. Overview

The BusBom Project consists of two main components for UART-based communication:

• STM32 firmware (built using STM32CubeIDE 1.18.1)
• Raspberry Pi 4 kernel module-based UART device driver (using serdev)

System Structure

• STM32 functions as the UART transmitter, Raspberry Pi as the receiver.
• Uses the serdev interface for kernel-level communication.

2. System Requirements

Item	Specification
MCU	STM32 series microcontroller
Development Tool	STM32CubeIDE 1.18.1
SBC	Raspberry Pi 4 (64bit)
OS	Raspberry Pi OS 64bit Legacy (Kernel 6.1.21-v8+)
Communication	UART (GPIO14: TX, GPIO15: RX)
Kernel Driver	serdev-based kernel module (manual build and load)

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3. STM32 Firmware Build and Upload

1. Launch STM32CubeIDE.
2. Select File → Open Projects from File System....
3. Set Directory to the busbom project folder path → Finish.
4. In Project Explorer, right-click on the busbom project → Build Project.
5. Connect the STM32 board.
6. Right-click on the project → Run As → 1 STM32 Cortex-M C/C++ Application.
   If the debug configuration window appears, click OK or Run.

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4. Raspberry Pi Setup and Driver Installation

4.1 UART Hardware Connection

Raspberry Pi Pin	Signal	Example Color
Pin 6	GND	Gray
Pin 8 (GPIO14)	TX	Purple
Pin 10 (GPIO15)	RX	Blue

4.2 Install Packages and Kernel Headers

sudo apt update
sudo apt install raspberrypi-kernel-headers
ls /lib/modules/$(uname -r)
# Ensure the 'build' folder exists

4.3 Edit Configuration Files

sudo chmod +w /boot/config.txt
sudo chmod +w /boot/cmdline.txt

Add to /boot/config.txt:

enable_uart=1
dtoverlay=disable-bt
dtoverlay=serdev_overlay

Remove from /boot/cmdline.txt:

console=serial0,115200

4.4 Disable Bluetooth

sudo systemctl disable hciuart
sudo systemctl stop hciuart
sudo systemctl disable bluetooth
sudo systemctl stop bluetooth

4.5 Configure Serial Port with raspi-config

sudo raspi-config
# Interface Options → Serial Port
# "Login shell over serial" → No
# "Enable serial port hardware" → Yes
sudo reboot

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5. Build and Load the Kernel Module

5.1 Download and Build Driver Source

git clone https://github.com/BusBom/hardware.git
cd hardware/uart/driver
make

5.2 Enable Time Synchronization

sudo timedatectl set-ntp true
timedatectl status
# Check that 'System clock synchronized: yes'

5.3 Load Kernel Module and Test

sudo cp serdev_overlay.dtbo /boot/overlays/
sudo insmod serdev_uart.ko
sudo dmesg -c
# Look for "serdev_echo: probe called"

5.4 Remove Module (if needed)

sudo rmmod serdev_uart

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6. Run the Test Program

cd ..
make
sudo ./uart

Example Output

Written time range: 0830:2130
Written bus array: 1234:5678:A0B1:M1M2
Connection state: CONNECTED

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7. Driver Usage

write() Function

• Set bus numbers: "BUS1:BUS2:BUS3:BUS4"
  Use a space character (' ') for empty platforms.
  Example: "6001: :6003:6004"

• Set operating time: "START_TIME:END_TIME" (24-hour format)
  Example: "0910:0012" → 9:10 AM to 12:12 AM
  Example: "1612:2010" → 4:12 PM to 8:10 PM

echo "0100:2100" | sudo tee /dev/serdev-uart
echo "6001:6002:6003:6004" | sudo tee /dev/serdev-uart

read() Function

• Check connection status:
  • 1 : Connected
  • 0 : Disconnected

cat /dev/serdev-uart

⚠ Note: Initial connection may take some time.

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8. Reference Diagrams

• STM32 Firmware Architecture
  

• Raspberry Pi Driver Architecture
  

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9. Troubleshooting

Symptom	Cause and Solution
No serdev-uart device	Check /boot/config.txt and kernel module settings
No "probe called" message	Verify with dmesg after insmod
cat /dev/serdev-uart returns 0	Check STM32 connection or TX/RX wiring
write() has no effect	Format error or /dev/serdev-uart permission issue