Home » Computers, pcDuino » pcDuino U-Boot – Part 1

This evening I decided it was time to check out the boot loader and boot command options on the pcDuino. To access the serial port on the J5 debug port I used a Sparkfun FTDI Basic Breakout-3.3v — a simple to use logic level serial to USB interface. With the power off and the FTDI Basic disconnected from the computer, I connected the serial lines and ground.

pcDuiono J5 Pin FTDI Basic Description
1 – RX 3 – TXO pcDuino to FTDI serial data
2 – GND 6 – GND common signal reference
3 – TX 2 – RXI FTDI to pcDuino serial data

After double checking the connections, I plugged the FTDI Basic into my Windows laptop computer. After confirming the port assignment, I used TeraTerm to open the serial port on my computer. The serial communication configuration needed to be set for 115200 Baud, 8-bit, No parity, 1 stop bit, no flow control, and the serial port assigned by Windows to the FTDI Basic.

Power On and Boot

After applying power to the pcDuino, the bootloader (U-Boot) startup sequence showed in the terminal window, followed by the familiar Linux boot messages as the kernel was loaded and Linux started. Surprisingly, at the end of the Linux boot, I was presented with a root prompt. Instead of presenting a login prompt, the debug port goes directly to a root shell. This I will need to change!

U-Boot Fun

Now for the real reason I wanted to try this. Access to U-Boot and the boot command line.

In the serial terminal window, I rebooted the pcDuino…

… and interrupted the U-Boot start up by pressing the space bar at the “Hit any key to stop autoboot” prompt.

Greeted by the U-Boot prompt. No to check for what commands are available for modifying the environment using the help command.

Current environment settings.

Interesting. By default, the A10 settins are loaded to memory from evb.bin and the kernel is loaded from uImage from the NAND flash /boot partition. The default kernel command line sets /root to the NAND flash root partition. Then off it goes.


My next project is to get the pcDuino booting from the SDCARD. All of the pieces are present for accomplishing this. Stay tuned for Part 2 later tonight. Right now, it is dinner time.

Update 14-Mar-2013: For those interested in Part 2 — where I planned on enabling automatic SD booting, there has been a delay. The U-Boot implementation on the pcDuino is crippled. It does not have the ability to save an updated environment to NAND flash and does not support the newer boot.scr or uEnv.txt files. I am currently in the process of creating a U-Boot for pcDuino that will support SD card booting without removing the NAND flash support.


ONLY TRY THE ABOVE IF YOU UNDERSTAND WHAT YOU ARE DOING. Connecting to the serial debug port has the potential to damage your pcDuino if your connections are incorrect. Changes to the U-Boot environment can render your pcDuino unbootable. YOU HAVE BEEN WARNED!

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3 Responses to “pcDuino U-Boot – Part 1”

  1. BB
    March 13th, 2013 at 18:39 | #1

    “Surprisingly, at the end of the Linux boot, I was presented with a root prompt. Instead of presenting a login prompt, the debug port goes directly to a root shell. This I will need to change!”

    Hi Bill,
    Not sure if this helps.

    From: http://linux-sunxi.org/More-images

    “to get rid of annoying root autologins rename “/etc/init/openvt.conf” to “/etc/init/openvt.conf.noboot” and edit “/etc/default/autogetty” to disable tty and serial autologin”

    Thanks for sharing!

  2. March 13th, 2013 at 19:43 | #2

    Thank you for the info. I’ll look into it.

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    September 12th, 2014 at 07:03 | #3

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