Board communication

We could use the HDMI port to connect a screen to the board and manage it like a regular computer. However this method would defeat the purpose of having an embedded platform that could end up in an environment that does not require or even allow access to a screen.

This page will demonstrate a few methods to access and manage the board without the need to connect a screen or any control peripherals.

UART debug connection

This method does not require to have a working OS on the board, it's thus useful to debug things that may prevent one to correctly boot.

The 6 pins next to one of the GPIO header, with J1 indicated on the silkscreen, is a UART debug port. The dot on the silkscreen indicates the first pin and three pins actually interest us: Ground, RX and TX. Connect them correctly to a USB-to-UART converter:

Pin	On BBB	On converter	Colour (if using a FTDI TTL-232R cable
1	Ground	Ground	Black
4	RX	TX	Orange
5	TX	RX	Yellow

Once it's done, power the board. You should see a new device appear in your /dev directory, such as /dev/ttyUSB0.

We can now connect to that device, for example using picocom (you may need to install it first). According to eLinux wiki, the baudrate is 115200 and all other communication parameters are the defaults. We can establish a serial connection with the board like so:

$ picocom -b 115200 /dev/ttyUSB0

Press the reset button next to the USB port on the board to witness the full booting procedure. You should then be welcomed with a login prompt with default login:password debian:temppwd if you installed the [pre-built image](picocom -b 115200 /dev/ttyUSB0).

SSH connection

If you installed a pre-built Linux image or configured one correctly, the OS should create a network interface using the USB connection between the board and your computer.

There are a few methods to discover the IP of the board.

1. From a debug console running through UART, we can see the IP assigned to the USB network connection.

$ ip a
[...]
5: usb0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
    link/ether 84:eb:18:97:ef:16 brd ff:ff:ff:ff:ff:ff
    inet 192.168.7.2/24 brd 192.168.7.255 scope global usb0
       valid_lft forever preferred_lft forever

2. From your local computer, check the sub-network of the newly created interface and scan it using nmap.

$ ip a
[...]
5: enp5s0f3u2u3u3: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UNKNOWN group default qlen 1000
    link/ether 84:eb:18:97:ef:17 brd ff:ff:ff:ff:ff:ff
    inet 192.168.7.1/24 brd 192.168.7.255 scope global dynamic noprefixroute enp5s0f3u2u3u3
       valid_lft 106sec preferred_lft 106sec

$ nmap -sn 192.168.7.0/24
Starting Nmap 7.93 ( https://nmap.org ) at 2023-04-04 12:34 CEST
Nmap scan report for 192.168.7.1
Host is up (0.00012s latency).
Nmap scan report for 192.168.7.2
Host is up (0.00064s latency).

$ nmap -sV -p 22 192.168.7.2
Starting Nmap 7.93 ( https://nmap.org ) at 2023-04-04 12:36 CEST
Nmap scan report for 192.168.7.2
Host is up (0.00046s latency).

PORT   STATE SERVICE VERSION
22/tcp open  ssh     OpenSSH 7.9p1 Debian 10+deb10u2 (protocol 2.0)
Service Info: OS: Linux; CPE: cpe:/o:linux:linux_kernel

We know the IP of the board is 192.168.7.2 in this instance, and we confirmed that port 22 is open and running an SSH service. We can thus connect to the board like so:

$ ssh debian@192.168.7.2

Send and receive files

To exchange file with the board, we can use an SSH connection through scp.

On your local computer, create a test file and then send it to the board:

$ echo "Hello world!" > hello.txt
$ scp hello.txt debian@192.168.7.2:/home/debian/

Check on the board that the file was correctly received!