Embedded_Linux_Booting

General Booting
ROM code X - Loader U - Boot Kernel
Internal ROM Internal SRAM External DDR External DDR

Booting Process
● X – loader :
– Basic hardware init (GPIO, clock, SDRAM, etc)
– Load and start u-boot
● U – boot :
– Hardware initializations
– Load and start kernel
● Kernel :
– Drivers initializations
– Mount root file system
● Init :
– First user-space processes
– Launch RC scripts
– Start graphic environment

ROM code
● After a processor is reset, it executes ROM startup
code
● The ROM startup code initializes the cpu, memory
controller and on-chip devices, and it configures the
memory map
● Searches the booting devices for a valid booting
image
● Loads the x-loader into SRAM and executes it

X - loader
● It is first stage boot loader
● It is also called as MLO(Memory LOader)
● Runs in an Internal SRAM
● Initializes clocks and memory
● Loads the second stage boot loader(u-boot) in
SDRAM and executes it

U - boot
● U-boot is Universal boot loader, an open
source boot loader
● Performs some additional platform
initialization
● Sets the boot arguments
● Passes control to the kernel image

Kernel
● Decompress the kernel into SDRAM
● Sets up peripherals, such as LCD, HDMI, I2C,
bus, USB, SD card, audio, etc
● Mounts the root file system that contains all
userspace libraries/applications
● Root file system then executes init process

Booting Techniques
1. Flash Memory
2. EMMc/SD card
3. TFTP/NFS
4. UART/USB

● By default, the ROM code in the Sitara AM3359 will
boot from the MMC1 interface first (the onboard
eMMC), followed by MMC0 (external uSD), UART0
and USB0.
● If the boot switch (S2) is held down during power-up,
the ROM will boot from the SPI0 Interface first,
followed by MMC0 (external uSD), USB0 and UART0.
● This allows the BeagleBone Black to bypass the
onboard eMMC and boot from the removable uSD
(provided no valid boot device is found on SPI0.) This
can be used to recover from a corrupted onboard
eMMC/U-Boot.

Booting from flash:
● Since default boot is from nand flash, nothing
to be done by us for booting from flash.
● Connect usb-to-serial convertor from board to
pc for console (“minicom”).
● Power the board with usb cable, now the board
automatically boots from flash and it will ask
for login, use “root” it will not ask password
for root. Now you will be getting beaglebone
login prompt.

Recovering flash memory:
● By default it will boot from flash memory.
● If it is not booted, here are steps to boot from
flash
● Unable to boot from flash memory then :
copy beaglebone image to sd card using:
● Insert sd card to board, holding down user
boot button power up the board and wait until
you see the user leds on, now release boot
button
sudo dd if=bone-debian-7.8-lxde-4gb-armhf-2015-03-01-4gb.img of=/dev/sdbsudo dd if=bone-debian-7.8-lxde-4gb-armhf-2015-03-01-4gb.img of=/dev/sdbsudo dd if=bone-debian-7.8-lxde-4gb-armhf-2015-03-01-4gb.img of=/dev/sdbsudo dd if=bone-debian-7.8-lxde-4gb-armhf-2015-03-01-4gb.img of=/dev/sdbsudo dd if=bone-debian-7.8-lxde-4gb-armhf-2015-03-01-4gb.img of=/dev/sdbsudo dd if=bone-debian-7.8-lxde-4gb-armhf-2015-03-01-4gb.img of=/dev/sdbsudo dd if=bone-debian-7.8-lxde-4gb-armhf-2015-03-01-4gb.img of=/dev/sdbsudo dd if=bone-debian-7.8-lxde-4gb-armhf-2015-03-01-4gb.img of=/dev/sdb

● Login : root
● U get this prompt as below
– root@beagleBone:~#
– In that use this command
vi /boot/uEnv.txt
In this file, you find last line was commented.
Release that comment and save the file
● Then remove sd card and boot
● It will boot from flash memory

Booting from uSD card:
● To boot from uSD card, first we have to
copy bootloaders and rootfilesystem to
uSD card.
● Before you do copy, we have to partition
the uSD card
1. FAT filesystem and Bootable
2.Linux filesystem

● After Partitioning the SD card, it will be like this :
Disk /dev/sdb: 7.4 GiB, 7948206080 bytes, 15523840 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x00000000
Device Boot Start End Sectors Size Id Type
/dev/sdb1 * 2048 198655 196608 96M e W95 FAT16
(LBA)
/dev/sdb2 198656 7577599 7378944 3.5G 83 Linux

● After partioning, create file system on newly
created partitions using commands:
1. sudo mkfs.vfat -F 32 /dev/sdb1 -n boot
2. sudo mke2fs -L RootFs /dev/sdb2
● Copy files to partions Boot and RootFs:
– MLO, u-boot.img, user.txt, uEnv.txt, .dtb files to
Boot
– RootFs.xz to RootFs (extract after copying to sd
card)
● Insert SD card to board for booting

● To boot from uSD card, hold down the user boot
button and power up the board

Demo of Stage by Stage booting
● First copy the MLO source code to sd card and
insert to board
● Boot from sd card
● ROM code finds the MLO in sd card and starts
booting
● MLO searches for u-boot.img and there is no
u-boot.img
● It throws an error message as “error reading
u-boot.img”

● After that copy environment variables and .dtb
file in sd card
● Now u-boot.img find all those files it needed and
boots
● U-boot.img now loads and starts the kernel
● Finally booted from sd card, both login and
password as 'ubuntu'
● Now it is booted and you get prompt like this
ubuntu

● After that copy environment variables and .dtb
file in sd card
● Now u-boot.img find all those files it needed
and boots
● U-boot.img now loads and starts the kernel
● Finally booted from sd card, both login and
password as 'ubuntu'
● Now it is booted and you get prompt like this
ubuntu@ubuntu-armhf:~$

Booting from TFTP server
● Copy the uImage and .dtb files to path: /tftpboot
● We are going to boot u-boot through sd card, so copy those
files in sd card
● Install nfs server
sudo apt-get install rpcbind nfs-kernel-server
● Edit /etc/exports
/home
192.168.0.0/255.255.255.0(rw,sync,no_subtree_check)
/usr/local
192.168.0.0/255.255.255.0(rw,sync,no_subtree_check)
● After editing exports do:
sudo exportfs -ra

● Place the root file system in nfs
● User.txt in sd card contents:
serverip=192.168.1.5
ipaddr=192.168.1.6
nfsargs= setenv bootargs mpurate=${mpurate} console=$
{console} vram=${vram} root=/dev/nfs
nfsroot=192.168.1.5:/home/asvkarthick/workspace/Beagleb
one_black/sysplay/Templates/BootingNfs/NFS,nolock
rootdelay=15 ip=dhcp,rsize=1024,wsize=1024
uenvcmd=run nfsargs;mmc rescan; tftpboot 0x81000000
am335x-boneblack.dtb; tftpboot 0x80200000 uImage;
bootm 0x80200000 - 0x81000000;

● Connect ethernet cable from board to pc
● Start the “minicom”
● Power up the board and before the board get booted, press
enter or any key continously so it will go to u-boot prompt
● Using dhcp command, get server and our ip address
● Set ip address and server ip address
setenv ipaddr 192.168.0.250
setenv serverip 192.168.0.251
● Next load the kernel and device tree blob
tftpboot 0x81000000 am335x-boneblack.dtb
tftpboot 0x80200000 uImage-BBB
● Boot from memory location, it will be booted now:
bootm 0x80200000 - 0x81000000

Booting From UART
● For this boot, flash memory should erased before the boot
● Connect the serial port, start minicom, reset the board, now
it will display
ccccccccccc
● cntrl+A & S, it display 4 options, select xmodem from that
option, select first stage boot loader, then ok. It will copy
this BL to RAM, it will initiate or load DDR.
● Use loadb <addr of DDR> , cntrl+A and S --> kermit, select
MLO again, write to nand flash
nand write <addr of DDR> <MLO offset> <size of MLO>

● Next execute by command:
go <addr of DDR>
● Then, load <addr of DDR> and using kermit mode send u-
boot.img(second stage bootloader), write to nand
nand write <addr of DDR> <u-boot offset> <size of u-
boot.img>
go <addr of DDR>
● Then, load <addr of DDR> and using kermit mode send
kernel (uImage), write to nand
nand write <DDR addr> <kernel offset> <sizeof kernel>

boot
● For every execute command it will run each
stage of bootloader and at last for kernel we
have to use “boot” command for loading
kernel
● Thus now all file got transfered or written to
flash(nand) and booted via serial

Thank You
Presentation by
RASHILA R R
raghupathy.rashila@adeptchips.com

Embedded_Linux_Booting

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