Questions about connecting UART console


#1

This maybe an obvious question.

I am flashing bootloader with the guide https://github.com/96boards/documentation/wiki/DragonBoard-820c-Getting-Started-With-Linux

In the guide,

In order to force the DB820c to boot from SD you need to configure S1 switch properly. S1 is on the back of the board underneath the micro SD slot. Set S1 to OFF,ON,ON,OFF
Connect a USB cable from the micro USB to your PC.
Connect UART console
Connect the power whilst holding S4 (Vol-Minus)

I should connect UART console. But I wonder what I need and how to connect 820c board with my host PC ?

Thanks!!


#2

Connecting UART is not mandatory but allow you to see boot/flash messages and access a Linux console. Typically, people use use a 1.8v FTDI USB cable or access UART via a mezzanine board (UART adapter, Audio).


#3

Where is pin 1?
How do you connect the UART expensing board?
A marker would be helpful.
There is nothing in the docs.


#4

You can find hardware documentation here: https://www.96boards.org/documentation/consumer/dragonboard820c/hardware-docs/

All 96boards consumer edition have the same pinout, you can some info on https://www.96boards.org/pinout/ as well.

If you speak about the UART mezzanine, there are actually pin markers on each side [1 2] and [39 40]. mezzanine should be plugged so that the micro-usb connector is outward-oriented.


#5

How to connect the UART:
You can reference to uart for 410c. Picture on page 6.


#6

Hi,

I too am trying to flash the 820C board, the instructions say nothing about a specific FTDI cable. They simply state a USB to micro-USB cable can be used. How does one connect to the board via terminal?

Here are the instructions as stated in the original post:

In order to force the DB820c to boot from SD you need to configure S1 switch properly. S1 is on the back of the board underneath the micro SD slot. Set S1 to OFF,ON,ON,OFF
Connect a USB cable from the micro USB to your PC.
Connect UART console
Connect the power whilst holding S4 (Vol-Minus)

Thanks


#7

Like I said, serial/FTDI cable is only here for debugging purpose, you should be able to flash your board with the micro-usb only. For connecting serial to you computer, you can use one of the mezzanine including a FTDI (UART mezzanine, Audio mezzanine…) or any other regular FTDI compatible with 1.8v IO level (YS232RL…) connected to Pin1 (GND), Pin11 (TX), Pin13(RX).


#8

Hi,

Thanks for your response. What specifically should I be typing in the terminal to access the fastboot for the board? I don’t see anything new under /dev/bus/usb when the 820c board is connected via micro-USB to my Ubuntu Desktop. I have also tried dmesg and nothing new shows up there either.

Thanks


#9

To boot in fastboot mode you have to power on the device while holding Vol (-) button, then your board should be enumerated and detected as a fastboot device. the fastboot devices command give a list of detected devices. If you see nothing in dmesg I would suggest to try with an other USB cable (some of them are for charging only, no data). If issue remain (device does not show up in dmesg) I suggest to try board recovery: https://www.96boards.org/documentation/consumer/dragonboard820c/installation/board-recovery.md.html.


#10

Thank you for your reply, since your reply to my other thread on fixing the plasma desktop fixed that issue I no longer have to consider reflashing the board. Thanks again