Booting Beagle Bone Black over UART

Hi Foks.! Welcome to my blog.

Yes, we are going to boot BBB (Beagle Bone Black) over UART, seems strange..? even I had the same opinion, but its importance is really know when you work on a new board bring up task. UART interface is very reliable and easy to configure, hence I prefer this as the best option as boot media/interface during bring up time, later we can verify other boot mechanism like boot from SPI/NAND/MMC.

Once we are at U-boot prompt we are almost done, we can chose how we want to load the kernel image and from the command line arguments we save the about file system and other extra env settings. 

To get started we need the following:

• BeagleBoneBlack (BBB) board
• Linux distribution based host machine ( I have Ubuntu 14.04)
• CP2102 USB2.0 to TTL UART serial converter module.
• 100-240V to 5V-1.0 or 2.0A  adapter/converter.

Note: With USB power BBB will not fall-back to UART boot mode, use power supply.  

Serial Connection:

Locate the 6-pin header on BBB, written as "J1" below the first pin on the PCB as show in the below picture.

 

• J1 = GND (Ground)
• J4 = RXD (Receive Data)
• J5 = TXD (Transmit Data)

 

CP2102 USB2.0 to TTL UART serial converter

Connect J4 (RXD) to TXD line of  CP2102 USB2.0 to TTL UART serial converter
Connect J5 (TXD) to RXD line of  CP2102 USB2.0 to TTL UART serial converter
Connect J1 (GND) to GND line of  CP2102 USB2.0 to TTL UART serial converter

This makes the serial console setup ready.


Download U-Boot Source :

gvk51@gvk:~$ mkdir src
gvk51@gvk:~$ cd src
gvk51@gvk:~/src$ git clone git://git.denx.de/u-boot.git

Initialize Build Environment : 

gvk51@gvk:~$ sudo apt-get install git u-boot-tools g++ gawk lzop texinfo git-core build-essential libncurses5-dev gcc-arm-linux-gnueabi

Install all the mentioned packages for making build smooth.
 


Building the Source:

After successful installation of packages we now start building the u-boot source, for use to boot from UART we need the following images u-boot-spl.bin & u-boot.img

gvk51@gvk:~/src$ mkdir images
gvk51@gvk:~/src$ u-boot
gvk51@gvk:~/src/u-boot$ make am335x_boneblack_defconfig
gvk51@gvk:~/src/u-boot$ make -j4
gvk51@gvk:~/src/u-boot$ cp ./u-boot.img ../images/
gvk51@gvk:~/src/u-boot$ cp ./spl/u-boot-spl.bin ../images/

Booting BBB from UART:

BBB has different boots modes like boot from eMMC, uSD, serial & usb. To change the boot mode there is a switch S2, holding the boot switch down during boot without a uSD card inserted will force the boot source to be the USB port and if nothing is detected on the USB client port, it will go to the serial port for download.

Host tools for UART boot:

I have used picocom host tool to boot from serial, install it as shown below

gvk51@gvk:~$ sudo apt-get install picocom lrzsz

cd to directory where we have copied images, that is src/images folder. Assuming you have connected serial-to-usb converter, then you see a device node say /dev/ttyUSB0 on your host machine. Launch picocom from the images folder.

Commands for picocom:

• sending a file: press Ctrl+a and then press Ctrl+s
• exit: Ctrl+a and then press Ctrl+x

Step1: Open a terminal, issue command sudo picocom -b 115200 /dev/ttyUSB0 --send-cmd "sx -vv", you will see the following output on the console.

picocom v1.7

port is            : /dev/ttyUSB0
flowcontrol     : none
baudrate is     : 115200
parity is          : none
databits are    : 8
escape is         : C-a
local echo is    : no
noinit is          : no
noreset is        : no
nolock is         : no
send_cmd is     : sx -vv
receive_cmd is : rz -vv
imap is            :
omap is           :
emap is           : crcrlf,delbs,

Terminal ready

Step2: give key-combination (ctrl+a and ctrl+s), then you will see the following prompt,

*** file:

enter the file name u-boot-spl.bin and hit enter, you will see 

sx -vv u-boot-spl.bin
Sending u-boot-spl.bin, 570 blocks: Give your local XMODEM receive command now.
 
Step3: Now holding the boot-mode switch apply power to BBB, make sure there is no uSD & no USB cable connected. picocom starts sending the first stage boot-loader u-boot-spl.bin over UART, you will see the following output, after successful transfer you will see the character 'C' as acknowledgement from BBB.
 

Xmodem sectors/kbytes sent:   0/ 0kRetry 0: Timeout on sector ACK
Retry 0: Timeout on sector ACK
Retry 0: Got 00 for sector ACK
Retry 0: NAK on sector
Bytes Sent:  73088   BPS:304                            

Transfer complete

*** exit status: 0

U-Boot SPL 2015.07-00256-g413978d-dirty (Aug 06 2015 - 11:52:06)
C

Step4:  After you see the acknowledgement give key combination ctrl+a and ctrl+s to send the u-boot.img.

*** file:

enter the file name u-boot.img and hit enter, here you need to be patient, transfer of u-boot takes around 2-3 minutes and after successful you don't see any acknowledgement 'C' from BBB, after that wait for another 1-2 minutes to see BBB restarting and halt it at u-boot prompt by pressing a key, you will see the below log.

*** file: u-boot.img

sx -vv u-boot.img
Sending u-boot.img, 3239 blocks: Give your local XMODEM receive command now.
Xmodem sectors/kbytes sent:   0/ 0kRetry 0: NAK on sector
Bytes Sent: 414720   BPS:4480                           

Transfer complete

*** exit status: 0
xyzModem - CRC mode, 3241(SOH)/0(STX)/0(CAN) packets, 3 retries
Loaded 414700 bytes

U-Boot 2015.07-00256-g413978d-dirty (Aug 06 2015 - 11:52:06 +0530)

       Watchdog enabled
I2C:   ready
DRAM:  512 MiB
MMC:   OMAP SD/MMC: 0
Card did not respond to voltage select!
MMC init failedNet:   <ethaddr> not set. Validating first E-fuse MAC
cpsw, usb_ether
Hit any key to stop autoboot:  0
U-Boot# 

Here is the complete log of the boot sequence.

picocom -b 115200 /dev/ttyUSB0 --send-cmd "sx -vv"
picocom v1.7

port is        : /dev/ttyUSB0
flowcontrol    : none
baudrate is    : 115200
parity is      : none
databits are   : 8
escape is      : C-a
local echo is  : no
noinit is      : no
noreset is     : no
nolock is      : no
send_cmd is    : sx -vv
receive_cmd is : rz -vv
imap is        : 
omap is        : 
emap is        : crcrlf,delbs,

Terminal ready

*** file: u-boot-spl.bin
sx -vv u-boot-spl.bin 
Sending u-boot-spl.bin, 570 blocks: Give your local XMODEM receive command now.
Bytes Sent:  73088   BPS:6471                            

Transfer complete

*** exit status: 0

U-Boot SPL 2015.07-00256-g413978d-dirty (Aug 06 2015 - 11:52:06)
C
*** file: u-boot.img
sx -vv u-boot.img 
Sending u-boot.img, 3239 blocks: Give your local XMODEM receive command now.
Xmodem sectors/kbytes sent:   0/ 0kRetry 0: NAK on sector
Bytes Sent: 414720   BPS:4480                            

Transfer complete

*** exit status: 0
 xyzModem - CRC mode, 3241(SOH)/0(STX)/0(CAN) packets, 3 retries
Loaded 414700 bytes


U-Boot 2015.07-00256-g413978d-dirty (Aug 06 2015 - 11:52:06 +0530)

       Watchdog enabled
I2C:   ready
DRAM:  512 MiB
MMC:   OMAP SD/MMC: 0
Card did not respond to voltage select!
MMC init failedNet:   <ethaddr> not set. Validating first E-fuse MAC
cpsw, usb_ether
Hit any key to stop autoboot:  0 
U-Boot# 

from u-boot its always up to you from where you load the kernel and filesystem.

To boot BBB with Network File System click this link: BBB booting with NFS

Download working images of "u-boot-spl.bin", "u-boot.img" and ".config" files from this LINK

Please leave your comments, it will be encouraging :)