Beaglebone Black won't show-up as /dev/ttyUSB

Question

I am trying to learn Linux by following instructions in "Mastering Embedded Linux Programming" by Chris Simmonds. By following the book and with some help from Stack_Overflow_1, i was able to build the MLO and u-boot.img.

However, when i connect USB cable to my PC and execute the ls /dev/tty* command, i cannot find any device with /dev/ttyUSB. All i can see are devices with /dev/tty0-63, /dev/ttyS0-31 and one /dev/ttyprintk.

Also, when i press down the S2 button and connect the USB cable, i can only see the power led glowing and nothing else.

I have properly built the u-boot (three attempts to get it right).

Also, as per the instructions in the book, i am only testing the u-boot stuff and yet to reach the kernal part.

If i remove the sd card and connect the USB, im an able to talk to my BBB over ssh (192.168.7.2).

How to i get the u-boot to work? Thank you!

TBR TBR · Accepted Answer · 2020-07-15T05:29:38

If you don't have one yet, I'd recommend to get a USB-to-serial device (3.3V Vref). You connect it to the debug UART (J1) which is located next to the P9 side. Nowadays those are very cheap and can cost below 1$. Ones that feature a genuine FTDI part will be 5-10$ at least.

The serial port you are referencing is only available once the device has passed through U-Boot, booted the kernel and finally userspace has set up the communications.

Especially when working with U-Boot and the Kernel, low level UART access is crucial.

As a further note, could it be that the Book refers to the (white) original Beaglebone? That has a FTDI USB-to-UART chip on board and will allow you even U-Boot access. You can do the same things if you have the above mentioned USB device.

Beaglebone Black won't show-up as /dev/ttyUSB

2 Answers