<s>
Das	B-Language
U-Boot	I-Language
(	O
subtitled	O
"	O
the	O
Universal	O
Boot	B-Application
Loader	I-Application
"	O
and	O
often	O
shortened	O
to	O
U-Boot	O
;	O
see	O
History	O
for	O
more	O
about	O
the	O
name	O
)	O
is	O
an	O
open-source	B-Application
,	O
primary	O
boot	B-Application
loader	I-Application
used	O
in	O
embedded	B-Architecture
devices	I-Architecture
to	O
package	O
the	O
instructions	O
to	O
boot	O
the	O
device	O
's	O
operating	O
system	O
kernel	O
.	O
</s>
<s>
It	O
is	O
available	O
for	O
a	O
number	O
of	O
computer	B-General_Concept
architectures	I-General_Concept
,	O
including	O
68k	B-Device
,	O
ARM	B-Architecture
,	O
Blackfin	B-General_Concept
,	O
MicroBlaze	B-Device
,	O
MIPS	B-Device
,	O
Nios	B-Device
,	O
SuperH	O
,	O
PPC	B-Architecture
,	O
RISC-V	B-Device
and	O
x86	B-Operating_System
.	O
</s>
<s>
U-Boot	O
is	O
both	O
a	O
first-stage	O
and	O
second-stage	O
bootloader	B-Application
.	O
</s>
<s>
onchip	O
ROM	O
of	O
the	O
ARM	B-Architecture
CPU	O
)	O
from	O
a	O
supported	O
boot	O
device	O
,	O
such	O
as	O
an	O
SD	O
card	O
,	O
SATA	O
drive	O
,	O
NOR	O
flash	O
(	O
e.g.	O
</s>
<s>
using	O
SPI	B-Architecture
or	O
I²C	O
)	O
,	O
or	O
NAND	O
flash	O
.	O
</s>
<s>
U-Boot	O
implements	O
a	O
subset	O
of	O
the	O
UEFI	B-Architecture
specification	O
as	O
defined	O
in	O
the	O
Embedded	B-Architecture
Base	O
Boot	O
Requirements	O
(	O
EBBR	O
)	O
specification	O
.	O
</s>
<s>
UEFI	B-Architecture
binaries	O
like	O
GRUB	B-Application
or	O
the	O
Linux	B-Application
kernel	O
can	O
be	O
booted	O
via	O
the	O
boot	B-Application
manager	I-Application
or	O
from	O
the	O
command-line	B-Application
interface	I-Application
.	O
</s>
<s>
U-Boot	O
runs	O
a	O
command-line	B-Application
interface	I-Application
on	O
a	O
console	O
or	O
a	O
serial	O
port	O
.	O
</s>
<s>
from	O
the	O
serial	O
port	O
or	O
network	O
,	O
manipulate	O
device	B-Operating_System
trees	I-Operating_System
,	O
and	O
work	O
with	O
environment	O
variables	O
(	O
which	O
can	O
be	O
written	O
to	O
persistent	O
storage	O
,	O
and	O
are	O
used	O
to	O
control	O
U-Boot	O
behavior	O
such	O
as	O
the	O
default	O
boot	O
command	O
and	O
timeout	O
before	O
auto-booting	O
,	O
as	O
well	O
as	O
hardware	O
data	O
such	O
as	O
the	O
Ethernet	O
MAC	O
address	O
)	O
.	O
</s>
<s>
Unlike	O
PC	O
bootloaders	B-Application
which	O
obscure	O
or	O
automatically	O
choose	O
the	O
memory	O
locations	O
of	O
the	O
kernel	O
and	O
other	O
boot	O
data	O
,	O
U-Boot	O
requires	O
its	O
boot	O
commands	O
to	O
explicitly	O
specify	O
the	O
physical	O
memory	O
addresses	O
as	O
destinations	O
for	O
copying	O
data	O
(	O
kernel	O
,	O
ramdisk	O
,	O
device	B-Operating_System
tree	I-Operating_System
,	O
etc	O
.	O
)	O
</s>
<s>
Because	O
U-Boot	O
'	O
s	O
commands	O
are	O
fairly	O
low-level	O
,	O
it	O
takes	O
several	O
steps	O
to	O
boot	O
a	O
kernel	O
,	O
but	O
this	O
also	O
makes	O
U-Boot	O
more	O
flexible	O
than	O
other	O
bootloaders	B-Application
,	O
since	O
the	O
same	O
commands	O
can	O
be	O
used	O
for	O
more	O
general	O
tasks	O
.	O
</s>
<s>
It	O
's	O
even	O
possible	O
to	O
upgrade	O
U-Boot	O
using	O
U-Boot	O
,	O
simply	O
by	O
reading	O
the	O
new	O
bootloader	B-Application
from	O
somewhere	O
(	O
local	O
storage	O
,	O
or	O
from	O
the	O
serial	O
port	O
or	O
network	O
)	O
into	O
memory	O
,	O
and	O
writing	O
that	O
data	O
to	O
persistent	O
storage	O
where	O
the	O
bootloader	B-Application
belongs	O
.	O
</s>
<s>
device	B-Operating_System
tree	I-Operating_System
or	O
ramdisk	O
image	O
)	O
into	O
memory	O
,	O
and	O
then	O
executing	O
the	O
kernel	O
with	O
the	O
appropriate	O
arguments	O
.	O
</s>
<s>
I²C	O
(	O
e.g.	O
</s>
<s>
SPI	B-Architecture
(	O
e.g.	O
</s>
<s>
This	O
way	O
,	O
rather	O
than	O
requiring	O
the	O
data	O
that	O
U-Boot	O
will	O
load	O
to	O
be	O
stored	O
at	O
a	O
fixed	O
location	O
on	O
the	O
storage	O
device	O
,	O
U-Boot	O
can	O
read	O
the	O
filesystem	O
to	O
search	O
for	O
and	O
load	O
the	O
kernel	O
,	O
device	B-Operating_System
tree	I-Operating_System
,	O
etc.	O
,	O
by	O
pathname	O
.	O
</s>
<s>
Device	B-Operating_System
tree	I-Operating_System
is	O
a	O
data	O
structure	O
for	O
describing	O
hardware	O
layout	O
.	O
</s>
<s>
Using	O
Device	B-Operating_System
tree	I-Operating_System
,	O
a	O
vendor	O
might	O
be	O
able	O
to	O
use	O
a	O
less	O
modified	O
mainline	O
U-Boot	O
on	O
otherwise	O
special	O
purpose	O
hardware	O
.	O
</s>
<s>
As	O
also	O
adopted	O
by	O
the	O
Linux	B-Application
kernel	O
,	O
Device	B-Operating_System
tree	I-Operating_System
is	O
intended	O
to	O
ameliorate	O
the	O
situation	O
in	O
the	O
embedded	B-Architecture
industry	O
,	O
where	O
a	O
vast	O
number	O
of	O
product	O
specific	O
forks	B-Application
(	O
of	O
U-Boot	O
and	O
Linux	B-Application
)	O
exist	O
.	O
</s>
<s>
The	O
project	O
's	O
origin	O
is	O
a	O
8xx	O
PowerPC	B-Architecture
bootloader	B-Application
called	O
8xxROM	O
written	O
by	O
Magnus	O
Damm	O
.	O
</s>
<s>
In	O
2002	O
a	O
previous	O
version	O
of	O
the	O
source	O
code	O
was	O
briefly	O
forked	B-Application
into	O
a	O
product	O
called	O
ARMBoot	B-Language
,	O
but	O
was	O
merged	O
back	O
into	O
the	O
PPCBoot	O
project	O
shortly	O
thereafter	O
.	O
</s>
<s>
This	O
marked	O
the	O
last	O
release	O
under	O
the	O
PPCBoot	O
name	O
,	O
as	O
it	O
was	O
renamed	O
to	O
reflect	O
its	O
ability	O
to	O
work	O
on	O
other	O
architectures	O
besides	O
the	O
PPC	B-Architecture
ISA	O
.	O
</s>
<s>
PPCBoot−	O
2.0.0	O
became	O
U−Boot−	O
0.1.0	O
in	O
November	O
2002	O
,	O
expanded	O
to	O
work	O
on	O
the	O
x86	B-Operating_System
processor	O
architecture	O
.	O
</s>
<s>
Additional	O
architecture	O
capabilities	O
were	O
added	O
in	O
the	O
following	O
months	O
:	O
MIPS32	O
in	O
March	O
2003	O
,	O
MIPS64	O
in	O
April	O
,	O
Nios	B-Device
II	I-Device
in	O
October	O
,	O
ColdFire	B-Device
in	O
December	O
,	O
and	O
MicroBlaze	B-Device
in	O
April	O
2004	O
.	O
</s>
<s>
The	O
current	O
name	O
Das	B-Language
U-Boot	I-Language
adds	O
a	O
German	O
definite	O
article	O
,	O
to	O
create	O
a	O
bilingual	O
pun	B-Application
on	O
the	O
classic	O
1981	O
German	O
submarine	O
film	O
Das	B-Application
Boot	I-Application
,	O
which	O
takes	O
place	O
on	O
a	O
World	O
War	O
II	O
German	O
U-boat	B-Operating_System
.	O
</s>
<s>
It	O
is	O
free	B-Application
software	I-Application
released	O
under	O
the	O
terms	O
of	O
the	O
GNU	B-License
General	I-License
Public	I-License
License	I-License
.	O
</s>
<s>
It	O
can	O
be	O
built	O
on	O
an	O
x86	B-Operating_System
PC	O
for	O
any	O
of	O
its	O
intended	O
architectures	O
using	O
a	O
cross	O
development	O
GNU	O
toolchain	B-Application
,	O
for	O
example	O
crosstool	O
,	O
the	O
Embedded	B-Architecture
Linux	B-Application
Development	O
Kit	O
(	O
ELDK	O
)	O
or	O
OSELAS.Toolchain	O
.	O
</s>
<s>
The	O
importance	O
of	O
U-Boot	O
in	O
embedded	B-Architecture
Linux	B-Application
systems	O
is	O
quite	O
succinctly	O
stated	O
in	O
the	O
book	O
Building	O
Embedded	B-Architecture
Linux	B-Application
Systems	O
,	O
by	O
Karim	O
Yaghmour	O
,	O
whose	O
text	O
about	O
U-Boot	O
begins	O
,	O
"	O
Though	O
there	O
are	O
quite	O
a	O
few	O
other	O
bootloaders	B-Application
,	O
'	O
Das	B-Language
U-Boot	I-Language
'	O
,	O
the	O
universal	O
bootloader	B-Application
,	O
is	O
arguably	O
the	O
richest	O
,	O
most	O
flexible	O
,	O
and	O
most	O
actively	O
developed	O
open	O
source	O
bootloader	B-Application
available.	O
"	O
</s>
<s>
The	O
ARM-based	O
Chromebooks	B-Operating_System
ship	O
with	O
U-Boot	O
.	O
</s>
<s>
The	O
Celeron	O
-	O
and	O
i5-based	O
Chromebooks	B-Operating_System
use	O
it	O
as	O
payload	O
for	O
coreboot	B-Device
.	O
</s>
<s>
The	O
PowerPC	B-Architecture
based	O
series	O
of	O
AmigaOne	B-Device
computers	O
running	O
AmigaOS	B-Application
use	O
U-Boot	O
,	O
in	O
particular	O
the	O
Sam440ep	B-Device
and	O
Sam460ex	B-Device
by	O
ACube	O
Systems	O
Srl	O
,	O
and	O
the	O
AmigaOne	B-Device
X5000	O
by	O
A-Eon	O
,	O
the	O
successor	O
of	O
the	O
AmigaOne	B-Device
X1000	I-Device
.	O
</s>
<s>
Amazon	B-General_Concept
Kindle	I-General_Concept
&	O
Kobo	O
eReader	O
devices	O
use	O
U-Boot	O
as	O
their	O
bootloader	B-Application
.	O
</s>
<s>
TP-Link	O
and	O
several	O
other	O
OpenWRT/LEDE	O
compatible	O
MIPS	B-Device
based	O
wireless	O
routers	O
use	O
U-Boot	O
for	O
bootloading	O
.	O
</s>
<s>
Teltonika	O
cellular	O
routers	O
use	O
bootloader	B-Application
based	O
on	O
U-Boot	O
.	O
</s>
<s>
Asahi	O
Linux	B-Application
uses	O
it	O
as	O
payload	O
for	O
m1n1	O
in	O
order	O
to	O
boot	O
Linux	B-Application
on	O
Apple	B-Device
Silicon	I-Device
Mac	O
.	O
</s>
