<s>
Xinu	B-Operating_System
Is	O
Not	O
Unix	B-Application
(	O
Xinu	B-Operating_System
,	O
a	O
recursive	O
acronym	O
)	O
,	O
is	O
an	O
operating	B-General_Concept
system	I-General_Concept
for	O
embedded	B-Architecture
systems	I-Architecture
,	O
originally	O
developed	O
by	O
Douglas	O
Comer	O
for	O
educational	O
use	O
at	O
Purdue	O
University	O
in	O
the	O
1980s	O
.	O
</s>
<s>
The	O
name	O
is	O
both	O
recursive	O
,	O
and	O
is	O
Unix	B-Application
spelled	O
backwards	O
.	O
</s>
<s>
It	O
has	O
been	O
ported	O
to	O
many	O
hardware	O
platforms	O
,	O
including	O
the	O
DEC	B-Device
PDP-11	I-Device
and	O
VAX	B-Device
systems	O
,	O
Motorola	B-Device
68k	I-Device
(	O
Sun-2	B-Device
and	O
Sun-3	B-Device
workstations	I-Device
,	O
AT&T	B-Device
UNIX	I-Device
PC	I-Device
,	O
MECB	B-Device
)	O
,	O
Intel	B-Operating_System
x86	I-Operating_System
,	O
PowerPC	B-Device
G3	I-Device
,	O
MIPS	B-Device
,	O
ARM	B-Architecture
architecture	I-Architecture
and	O
AVR	O
(	O
atmega328p/Arduino	O
)	O
.	O
</s>
<s>
Xinu	B-Operating_System
was	O
also	O
used	O
for	O
some	O
models	O
of	O
Lexmark	O
printers	O
.	O
</s>
<s>
Despite	O
its	O
name	O
suggesting	O
some	O
similarity	O
to	O
Unix	B-Application
,	O
Xinu	B-Operating_System
is	O
a	O
different	O
type	O
of	O
operating	B-General_Concept
system	I-General_Concept
,	O
written	O
with	O
no	O
knowledge	O
of	O
the	O
Unix	B-Application
source	O
code	O
,	O
or	O
compatibility	O
goals	O
.	O
</s>
<s>
It	O
uses	O
different	O
abstractions	O
,	O
and	O
system	B-Operating_System
calls	I-Operating_System
,	O
some	O
with	O
names	O
matching	O
those	O
of	O
Unix	B-Application
,	O
but	O
different	O
semantics	O
.	O
</s>
<s>
Xinu	B-Operating_System
first	O
ran	O
on	O
the	O
LSI-11	O
platform	O
.	O
</s>
<s>
A	O
Motorola	B-Device
68000	I-Device
port	O
was	O
done	O
by	O
Derrick	O
Burns	O
in	O
1984	O
.	O
</s>
<s>
A	O
VAX	B-Device
port	O
was	O
done	O
in	O
1986	O
by	O
Comer	O
and	O
Tom	O
Stonecypher	O
,	O
an	O
IBM	O
PC	O
compatible	O
port	O
in	O
1988	O
by	O
Comer	O
and	O
Timothy	O
Fossum	O
,	O
a	O
second	O
Motorola	B-Device
68000	I-Device
(	O
Sun	B-Device
3	I-Device
)	O
port	O
circa	O
1988	O
by	O
Shawn	O
Ostermann	O
and	O
Steve	O
Chapin	O
,	O
a	O
Macintosh	B-Device
platform	O
port	O
in	O
1989	O
by	O
Comer	O
and	O
Steven	O
Munson	O
,	O
an	O
Intel	B-General_Concept
80486	I-General_Concept
version	O
by	O
John	O
Lin	O
in	O
1995	O
,	O
a	O
SPARC	B-Architecture
port	O
by	O
Jim	O
Griffioen	O
,	O
and	O
a	O
PowerPC	B-Architecture
port	O
in	O
2005	O
and	O
MIPS	B-Device
port	O
of	O
Embedded	O
Xinu	B-Operating_System
in	O
2006	O
by	O
Dennis	O
Brylow	O
.	O
</s>
<s>
Dennis	O
Brylow	O
at	O
Marquette	O
University	O
has	O
ported	O
Xinu	B-Operating_System
to	O
both	O
the	O
PowerPC	B-Architecture
and	O
MIPSEL	B-Device
processor	B-General_Concept
architectures	B-General_Concept
.	O
</s>
<s>
Porting	O
Xinu	B-Operating_System
to	O
reduced	B-Architecture
instruction	I-Architecture
set	I-Architecture
computing	I-Architecture
(	O
RISC	B-Architecture
)	O
architectures	B-General_Concept
greatly	O
simplified	O
its	O
implementation	O
,	O
increasing	O
its	O
ability	O
to	O
be	O
used	O
as	O
a	O
tool	O
for	O
teaching	O
and	O
research	O
.	O
</s>
<s>
MIPSEL	B-Device
was	O
chosen	O
as	O
a	O
target	O
architecture	O
due	O
to	O
the	O
proliferation	O
of	O
the	O
MIPSEL-based	O
WRT54GL	B-Application
router	O
and	O
the	O
cool	O
incentive	O
that	O
motivates	O
some	O
students	O
to	O
become	O
involved	O
in	O
projects	O
.	O
</s>
<s>
The	O
first	O
embedded	O
Xinu	B-Operating_System
systems	O
laboratory	O
based	O
on	O
the	O
WRT54GL	B-Application
router	O
was	O
developed	O
at	O
Marquette	O
University	O
.	O
</s>
<s>
In	O
collaboration	O
with	O
the	O
Marquette	O
Xinu	B-Operating_System
team	O
,	O
an	O
embedded	O
Xinu	B-Operating_System
laboratory	O
was	O
formed	O
at	O
the	O
University	O
of	O
Mississippi	O
,	O
laying	O
the	O
groundwork	O
for	O
further	O
work	O
on	O
developing	O
a	O
Virtual	O
Xinu	B-Operating_System
Laboratory	O
.	O
</s>
<s>
Embedded	O
Xinu	B-Operating_System
is	O
a	O
fresh	O
reimplementation	O
of	O
the	O
Xinu	B-Operating_System
design	O
,	O
in	O
ANSI	O
C	B-Language
,	O
on	O
an	O
embedded	O
RISC	B-Architecture
architecture	O
.	O
</s>
<s>
The	O
MIPS	B-Device
port	O
of	O
Embedded	O
Xinu	B-Operating_System
was	O
developed	O
from	O
2006	O
to	O
2010	O
at	O
Marquette	O
University	O
,	O
under	O
the	O
direction	O
of	O
Dr.	O
Dennis	O
Brylow	O
.	O
</s>
<s>
The	O
Embedded	O
Xinu	B-Operating_System
operating	B-General_Concept
system	I-General_Concept
is	O
copyright	O
(	O
c	B-Language
)	O
2007	O
,	O
2008	O
,	O
2009	O
,	O
and	O
2010	O
by	O
Douglas	O
Comer	O
and	O
Dennis	O
Brylow	O
.	O
</s>
<s>
The	O
first	O
successful	O
port	O
of	O
embedded	O
Xinu	B-Operating_System
was	O
completed	O
in	O
1994	O
,	O
when	O
it	O
was	O
implemented	O
in	O
a	O
Kenmore	O
model	O
728858	O
microwave	O
oven	O
produced	O
in	O
the	O
year	O
1990	O
.	O
</s>
<s>
The	O
Xinu	B-Operating_System
Laboratory	O
in	O
the	O
University	O
of	O
Mississippi	O
's	O
Department	O
of	O
Computer	O
and	O
Information	O
Science	O
was	O
formed	O
during	O
the	O
summer	O
of	O
2008	O
by	O
Dr.	O
Paul	O
Ruth	O
.	O
</s>
<s>
The	O
initial	O
laboratory	O
is	O
based	O
on	O
the	O
Marquette	O
University	O
Embedded	O
Xinu	B-Operating_System
Laboratory	O
.	O
</s>
<s>
Located	O
in	O
the	O
server	O
room	O
of	O
Weir	O
Hall	O
on	O
the	O
campus	O
of	O
the	O
University	O
of	O
Mississippi	O
,	O
is	O
composed	O
of	O
a	O
dozen	O
modified	O
Linksys	O
WRT54GL	B-Application
wireless	O
routers	O
,	O
a	O
32	O
port	O
Digi	O
Etherlite	O
serial	O
annex	O
,	O
a	O
24	O
port	O
10/100	O
Mbit/s	O
Ethernet	O
switch	O
,	O
a	O
BayTech	O
serial	O
controlled	O
power	O
strip	O
,	O
and	O
quite	O
a	O
few	O
wires	O
.	O
</s>
<s>
The	O
system	O
is	O
controlled	O
by	O
a	O
standard	O
PC	O
running	O
Debian	O
Linux	B-Application
.	O
</s>
<s>
The	O
WRT54G	B-Application
routers	O
use	O
the	O
MIPSEL	B-Device
architecture	O
and	O
are	O
used	O
as	O
backend	O
devices	O
on	O
which	O
the	O
Xinu	B-Operating_System
embedded	O
operating	B-General_Concept
system	I-General_Concept
runs	O
.	O
</s>
<s>
The	O
approach	O
focuses	O
on	O
low	O
cost	O
,	O
flexible	O
,	O
commodity	O
embedded	B-Architecture
hardware	I-Architecture
,	O
freely	O
available	O
development	O
and	O
debugging	O
tools	O
,	O
and	O
a	O
fresh	O
implementation	O
of	O
a	O
classic	O
operating	B-General_Concept
system	I-General_Concept
,	O
Embedded	O
Xinu	B-Operating_System
,	O
that	O
is	O
ideal	O
for	O
student	O
exploration	O
.	O
</s>
<s>
Virtual	O
Xinu	B-Operating_System
addresses	O
two	O
challenges	O
that	O
limit	O
the	O
effectiveness	O
of	O
Nexos	O
.	O
</s>
<s>
Ultimately	O
,	O
porting	O
the	O
Xinu	B-Operating_System
operating	B-General_Concept
systems	I-General_Concept
to	O
QEMU	B-Application
virtual	O
hardware	O
,	O
and	O
developing	O
the	O
virtual	O
networking	O
platform	O
have	O
produced	O
results	O
showing	O
success	O
using	O
Virtual	O
Xinu	B-Operating_System
in	O
the	O
classroom	O
during	O
one	O
semester	O
of	O
the	O
Operating	B-General_Concept
Systems	I-General_Concept
course	O
at	O
the	O
University	O
of	O
Mississippi	O
by	O
Dr	O
Ruth	O
.	O
</s>
<s>
There	O
are	O
several	O
versions	O
of	O
Xinu	B-Operating_System
available	O
for	O
platforms	O
such	O
as	O
an	O
x86	B-Operating_System
,	O
ARM	B-Architecture
,	O
AVR	O
(	O
Arduino	O
)	O
and	O
MIPS	B-Device
.	O
</s>
<s>
The	O
last	O
versions	O
by	O
Douglas	O
Comer	O
is	O
for	O
both	O
the	O
Intel	B-Operating_System
x86	I-Operating_System
(	O
Galileo	O
)	O
and	O
ARM	B-Application
Cortex-A8	I-Application
(	O
BeagleBone	O
Black	O
)	O
.	O
</s>
