Serial Port Communication - chaolunner/RaspberryPi GitHub Wiki

This is a tutorial about how to setup bluetooth on the raspberry pi and how to use serial port to communiate with raspberry pi.

UART configuration

For details, please click on the title link above. In brief,

The SoCs used on the Raspberry Pis have two built-in UARTs, a PL011 and a mini UART.

(Raspberry Pi 3 and Raspberry Pi Zero W), the PL011 UART is connected to the Bluetooth module, while the mini UART is used for Linux console output. On all other models the PL011 is used for the Linux console output.

The particular deficiencies of the mini UART compared to the PL011 are:

• No break detection
• No framing errors detection
• No parity bit
• No receive timeout interrupt
• No DCD, DSR, DTR or RI signals

So if you want to communicate through a USB connection, you may want to use a stronger PL011 UART on the Linux console output (This will inevitably affect the function of Bluetooth module). The specific implementation steps are as follows:

• First, find the /boot/overlays/pi3-miniuart-bt-overlay.dtb file or you need to download pi3-miniuart-bt. Refer to /boot/overlays/README for details on Device Tree Overlays.

• Use the command ls -l /dev in the Raspberry Pi command terminal to view the current serial port mapping relation of Raspberry Pi 3. By default you should see the following output:

  serial0 -> ttyS0
  serial1 -> ttyAMA0
  

  Linux console output = serial0, mini UART = ttyS0

  Bluetooth module = serial1, PL011 UART = ttyAMA0

• Next we need to edit the /boot/config.txt file, open the file either on your desktop computer or using the Raspberry Pi via SSH

  sudo nano /boot/config.txt

• You need to add the following lines:

  dtoverlay=pi3-miniuart-bt-overlay

  If you want to minimize the impact of Bluetooth module functionality, you may also need to add force_turbo=1

  For more information, please refer to force_turbo

• Exit and save your changes

  https://github.com/chaolunner/RaspberryPi/wiki/images/config-text.png

• Now edit /boot/cmdline.txt

  sudo nano /boot/cmdline.txt

• Change the file to the following:

  dwc_otg.lpm_enable=0 console=serial1,115200  console=tty1 root=/dev/mmcblk0p2  kgdboc=serial1,115200 rootfstype=ext4 elevator=deadline fsck.repair=yes  rootwait
  

• Exit and save your changes

• If you want to disable the built in bluetooth you need to stop hciattach trying to use the modem via uart0 which will disable the relevant systemd service

  sudo systemctl disable hciuart

• Now edit /lib/systemd/system/hciuart.server and replace ttyAMA0 with ttyS0.

  sudo nano /lib/systemd/system/hciuart.service

• Replace ttyAMA0 with ttyS0

• Exit and save your changes

  https://github.com/chaolunner/RaspberryPi/wiki/images/hciuart-service.png

• You need to update the operating system with the latest patches with:

  sudo apt-get update

  sudo apt-get upgrade

  sudo reboot

• Once your Raspberry Pi 3 has rebooted you should now have access to the serial console via the GPIO header at 115,200 baud.

  https://github.com/chaolunner/RaspberryPi/wiki/images/uart-login-success.png

• If you want to use the hardware UART without the serial console you do not need to make the changes to the cmdline.txt file as shown above.

Bluetooth

• In a terminal on the Pi, run this command sdptool browse local

  If you encounter the situation shown in the following figure:

  https://github.com/chaolunner/RaspberryPi/wiki/images/sdptool-browse-local.png

  • First, you need to setup the Serial Port Profile (SPP) on the Raspberry Pi. Edit this file:

    sudo nano /etc/systemd/system/dbus-org.bluez.service

  • Add ' -C' at the end of the 'ExecStart=' line, to start the bluetooth daemon in 'compatibility' mode. Add a new 'ExecStartPost=' immediately after that line, to add the SP Profile. The two lines should look like this:

    ExecStart=/usr/lib/bluetooth/bluetoothd -C
    ExecStartPost=/usr/bin/sdptool add SP
    

    https://github.com/chaolunner/RaspberryPi/wiki/images/serial-port-profile.png

  • Save and reboot.

  • Then if you run this command sdptool browse local again, you should see the results shown in the following picture

    https://github.com/chaolunner/RaspberryPi/wiki/images/sdptool-browse-local-success.png

• Turn on Bluetooth and enable Make Discoverable on the Pi.

• Two way to make the rfcomm watch hci0:

  • The first, In a terminal on the Pi, run this command every time after reboot:

    sudo rfcomm watch hci0

  • The second:

    • You can automate the rfcomm command with a service unit. Create a new file with sudo

      sudo nano /etc/systemd/system/rfcomm.service

    • and enter the following

      [Unit]
      Description=RFCOMM service
      After=bluetooth.service
      Requires=bluetooth.service
      
      [Service]
      ExecStart=/usr/bin/rfcomm watch hci0
      
      [Install]
      WantedBy=multi-user.target
      

      https://github.com/chaolunner/RaspberryPi/wiki/images/rfcomm-service.png

    • Enable that to start at boot time with

      sudo systemctl enable rfcomm

    • Now either reboot or start it manually with

      sudo systemctl start rfcomm

    You also can use systemctl status rfcomm check the result of rfcomm service. If the operation is correct, you should see the following results:

    https://github.com/chaolunner/RaspberryPi/wiki/images/systemctl-status-rfcomm.png

• Use your devices eg. MacBook to connect with the Pi.

• Connection on Mac

  Port confirmation.

  https://github.com/chaolunner/RaspberryPi/wiki/images/port-confirmation.png

  Connect with screen /dev/tty.raspberrypi-SerialPort

• Connection confirmation

  On the Pi, open another terminal and enter the following command

  sudo echo "hello" > /dev/rfcomm0

  If the terminal on the Mac has a hello display, it is successful.

Code by Python

• Install pySerial

  pip install pyserial

  https://github.com/chaolunner/RaspberryPi/wiki/images/install-pyserial.png

• Use Terminal Confirmation Port

  python -m serials.tools.list_ports

  https://github.com/chaolunner/RaspberryPi/wiki/images/serials-tools-list_ports.png

• Use Python Confirmation Port

  import serial.tools.list_ports
  
  comports = list(serial.tools.list_ports.comports())
  
  if len(comports) <= 0:
    print("No port found!")
  else:
    for list_port_info in comports:
      print(list_port_info.device)
  

Communiate with Unity

The most important thing is not to forget to add a newline character to the end of the data to be sent! Otherwise, when you use the ReadLine() method, the program may be block.

• Raspberry Pi Part

  • serial_port_communication

• Unity Part

  • SerialHandler

  • SerialSystem

Linux User and Group Manage Commands

• cat /etc/group - Check the users in the groups.

• cat /etc/group | grep bluetooth - Check the users in the bluetooth group.

• sudo usermod -G bluetooth -a pi - Append pi user in the bluetooth group.

• sudo gpasswd -d pi bluetooth - Remove pi user in the bluetooth group.

Reference

Raspberry Pi 3 UART Overlay Workaround

RaspberryPi (jessie)とMac間のBluetooth通信

SerialPort または Uniduino を使った Unity と Arduino を連携させる方法調べてみた