BeagleBoard-xM Booting Process

© 2012-14 SysPlay Workshops <workshop@sysplay.in>
All Rights Reserved.
BeagleBoard Booting Process

2© 2012-14 SysPlay Workshops <workshop@sysplay.in>
What to Expect?
PC Booting Process
Beagle Booting Process
Booting through SD Card
Partitioning & Creating Root Filesystem
W's of Bootloaders
UBoot
Booting through Serial

PC Booting Process
System Startup
Stage 2 Bootloader
Stage 1 Bootloader
Kernel
Init
Power-Up /
Reset
Operation

General Booting of BeagleBoard
Image under “CC BY-SA 3.0 US” from http://omappedia.org/wiki/Bootloader_Project

DM3730 Processor Boot Modes
Memory Booting
NAND, NOR, MMC
Peripheral Booting
USB, UART
The Order / Sequence is determined by
The set of GPIO configuration pins called SYSBOOT pins (5
pins)
Default Booting Sequence
USB -> UART3 -> MMC1 -> NAND (for processor)
NAND-> USB-> UART3 -> MMC (for BeagleBoard)

(SD Card)
ROM code loads x-loader (MLO)
Performs External DRAM configuration
X-loader loads u-boot
Default location is /media/mmcblkp01/u-boot.bin
U-boot executes default environment/commands
Default location is /mmcblkp01/uEnv.txt
Commands load the Kernel
Default location is /media/mmcblkop2/boot/uImage
Kernel reads root file system

Recovering the Board
Copy the user.txt and u-boot.bin
tftp -g <serverip> -r u-boot_destroy.bin -l u-
boot.bin
tftp -g <serverip> -r user.txt -l user.txt
Change the ip address in user.txt
Delete the kernel - /boot/uImage
Delete the Root Filesystem.
Reboot the sytem.

SD Card Partitioning
Fdisk /dev/mmcblk0
Create a window partition of 116MB
Make it bootable
Create two primary Linux partitions of sizes
3GB and 1GB aprox.

Creating & Filling the Filesystem
Create the Filesystem of type Fat 32 on first partition
mkfs.vfat -F 32 /dev/mmcblk0p1 -n boot
Create the Filesystem of type ext2 on Second and third partitions
mke2fs -L FirstRootFs /dev/mmcblk0p2
mke2fs -L SecondRootFs /dev/mmcblk0p3
Fill the filesystem with contents
tftp -g 192.168.20.181 -r Narcisus.tgz
tar -zxvf Narcisus.tgz
Copy u-boot_destroy.bin, user.txt and uEnv.txt in vfat partition
tftp -g 192.168.20.181 -r u-boot_destroy.bin -l u-boot.bin
tftp -g 192.168.20.181 -r user.txt
tftp -g 192.168.20.181 -r uEnvAng.txt -l uEnv.txt

What is a Bootloader?
Also, referred to as boot monitor, is a small
piece of software that executes soon after
powering up a system
Simply, a loader (program), which boots up
(starts) the system
A Customized Program started by
Controller's Internal Code in Embedded
Systems, Or
External Pre-programmed Code (like BIOS) in
Desktops

Tasks of a Bootloader
Initialization Tasks
Memory Setup & Initialization
System Peripheral Initialization
for the kernel
Actual Task
Load the RAM-based File System, like initrd, initramfs, ...
Load the Kernel with proper arguments
Jump to the start of the Kernel
Additional Tasks
Multiple Kernel Boots

Design of Bootloaders
As Bootloader is started by a fixed code
It needs to be placed at a hard-coded
location
Hard-coded locations are not big enough for
the complete code (/ logic / tasks) of the
bootloader
Hence, it is typically split into 2 portions
Stage 1 – Small enough to load Stage 2 from our
desired location
Stage 2 – The actual bootloader we want to have

Bootloader Comparisons
On Desktops
Initialization Tasks are done by BIOS
Bootloader is to just Boot the Kernel
On Embedded Systems
All needs to be done by the Bootloader
But in an optimized way
Hence, the 2 bootloaders are
Quite different from each other
Later being more board dependent & constrained

Stage 2 Bootloader Flavours
Prevalent Desktop Bootloaders
LILO
GRUB
SYSLINUX
loadlin
Coreboot (Earlier called LinuxBIOS)
Popular Embedded System Bootloaders
BootLoader Object (BLOB)
Redboot
U-Boot

Check
Name the Stage 1 & Stage 2 bootloaders
Desktops
Embedded Systems

U-Boot

W's of U-Boot
Universal Bootloader (U-Boot)
An Open Source Bootloader
With minimal changes, can be ported for any
board
GRUB/LILO
Designed with x-86 in mind
Huge in Size
Needs to be changed drastically for porting on
other architecture

U-Boot Source Tree
arch – Architecture dependent Code
board – Board dependent Code
common – Environment & Command Line Code
doc – Documentation
drivers – Device specific Drivers
fs – File System support Code
include – Headers
lib – Compression, Encryption related Code
net – Minimal Network Stack
tools – U-Boot Utilities (mkimage is here)

U-boot Hands-on
Stopping at the U-Boot
Help - “?”
Commands
Booting: bootp, bootm, boot, ...
NOR Flash: erase, cp, protect, …
NAND Flash: nand
Miscellaneous: reset, ...
...
Environment Variables
printenv
setenv
saveenv

Booting through the Serial
Boot ROM can load any binary x-loader
image into the internal SRAM of 64K
For Serial Boot,
A simple ID is written out of the serial port
If host responds within that short window of
time
The ROM reads from serial port
Transfers the data to the internal SRAM
Control is passed to the start of the SRAM.

Steps For Serial Booting
Remove the SD Card
Load the X-loader
./pserial -p /dev/ttyS0 -f x-load.bin
Load the U-boot
./ukermit -p /dev/ttyS0 -f u-boot.bin
Prepare the board for the using Ethernet
usb start
setenv serverip 192.168.20.181
setenv ipaddr <ipaddr>
Load & Import the Environmental Variables
tftpboot EnvSerial.txt
run importbootenv
Run the command – run uenvcmd

U-Boot Compiling
Preparing the Makefile
Setup CROSS_COMPILE for cross compilation
Or, invoke make with these options
Configuring for a particular board
make <board>_config
Compiling for the configured board
make (Output would be u-boot.bin)
Cleaning up
make clean

Adding the Command in uboot
Create the file cmd_<file>.c
Fill the Macro 'U_BOOT_CMD()'
name : the name of the command
maxargs: the maximum number of arguments this function takes
command : function pointer (*cmd)(struct cmd_tbl_s *, int, int, char
*[])
usage : Short Description
help : Long description
Add the entry into common/Makefile
COBJS-$(CONFIG_CMD_<NAME>) += cmd_<file>.o
Include the macro CONFIG_CMD_<NAME> in board.h file

What all have learnt?
PC Booting Process
Booting through SD Card
Booting through Serial
Partitioning & Creating Root Filesystem
W's of Bootloaders
UBoot

Any Queries?

BeagleBoard-xM Booting Process

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