<s>
Contiki	B-Operating_System
is	O
an	O
operating	B-General_Concept
system	I-General_Concept
for	O
networked	O
,	O
memory-constrained	O
systems	O
with	O
a	O
focus	O
on	O
low-power	O
wireless	O
Internet	B-Operating_System
of	I-Operating_System
Things	I-Operating_System
(	O
IoT	B-Operating_System
)	O
devices	O
.	O
</s>
<s>
Contiki	B-Operating_System
is	O
used	O
for	O
systems	O
for	O
street	O
lighting	O
,	O
sound	O
monitoring	O
for	O
smart	B-Device
cities	I-Device
,	O
radiation	O
monitoring	O
and	O
alarms	O
.	O
</s>
<s>
It	O
is	O
open-source	B-Application
software	I-Application
released	O
under	O
the	O
BSD-3-Clause	B-Operating_System
license	O
.	O
</s>
<s>
Contiki	B-Operating_System
was	O
created	O
by	O
Adam	O
Dunkels	O
in	O
2002	O
and	O
has	O
been	O
further	O
developed	O
by	O
a	O
worldwide	O
team	O
of	O
developers	O
from	O
Texas	O
Instruments	O
,	O
Atmel	O
,	O
Cisco	O
,	O
ENEA	O
,	O
ETH	O
Zurich	O
,	O
Redwire	O
,	O
RWTH	O
Aachen	O
University	O
,	O
Oxford	O
University	O
,	O
SAP	O
,	O
Sensinode	O
,	O
Swedish	O
Institute	O
of	O
Computer	O
Science	O
,	O
ST	O
Microelectronics	O
,	O
Zolertia	O
,	O
and	O
many	O
others	O
.	O
</s>
<s>
Contiki	B-Operating_System
gained	O
popularity	O
because	O
of	O
its	O
built	O
in	O
TCP/IP	B-Protocol
stack	I-Protocol
and	O
lightweight	O
preemptive	B-Operating_System
scheduling	I-Operating_System
over	O
event-driven	B-Application
kernel	B-Operating_System
which	O
is	O
a	O
very	O
motivating	O
feature	O
for	O
IoT	B-Operating_System
.	O
</s>
<s>
The	O
name	O
Contiki	B-Operating_System
comes	O
from	O
Thor	O
Heyerdahl	O
's	O
famous	O
Kon-Tiki	O
raft	O
.	O
</s>
<s>
Contiki	B-Operating_System
provides	O
multitasking	O
and	O
a	O
built-in	O
Internet	B-Protocol
Protocol	I-Protocol
Suite	I-Protocol
(	O
TCP/IP	B-Protocol
stack	I-Protocol
)	O
,	O
yet	O
needs	O
only	O
about	O
10	O
kilobytes	O
of	O
random-access	B-Architecture
memory	I-Architecture
(	O
RAM	B-Architecture
)	O
and	O
30	O
kilobytes	O
of	O
read-only	B-Device
memory	I-Device
(	O
ROM	B-Device
)	O
.	O
</s>
<s>
A	O
full	O
system	O
,	O
including	O
a	O
graphical	B-Application
user	I-Application
interface	I-Application
,	O
needs	O
about	O
30	O
kilobytes	O
of	O
RAM	B-Architecture
.	O
</s>
<s>
Contiki	B-Operating_System
is	O
designed	O
to	O
run	O
on	O
types	O
of	O
hardware	O
devices	O
that	O
are	O
severely	O
constrained	O
in	O
memory	O
,	O
power	O
,	O
processing	O
power	O
,	O
and	O
communication	O
bandwidth	O
.	O
</s>
<s>
A	O
typical	O
Contiki	B-Operating_System
system	O
has	O
memory	O
on	O
the	O
order	O
of	O
kilobytes	O
,	O
a	O
power	O
budget	O
on	O
the	O
order	O
of	O
milliwatts	O
,	O
processing	O
speed	O
measured	O
in	O
megaHertz	O
,	O
and	O
communication	O
bandwidth	O
on	O
the	O
order	O
of	O
hundreds	O
of	O
kilobits/second	O
.	O
</s>
<s>
Such	O
systems	O
include	O
many	O
types	O
of	O
embedded	B-Architecture
systems	I-Architecture
,	O
and	O
old	O
8-bit	O
computers	O
.	O
</s>
<s>
Contiki	B-Operating_System
provides	O
three	O
network	O
mechanisms	O
:	O
the	O
uIP	B-Protocol
TCP/IP	B-Protocol
stack	I-Protocol
,	O
which	O
provides	O
IPv4	B-Protocol
networking	B-Architecture
,	O
the	O
uIPv6	O
stack	O
,	O
which	O
provides	O
IPv6	B-Protocol
networking	B-Architecture
,	O
and	O
the	O
Rime	O
stack	O
,	O
which	O
is	O
a	O
set	O
of	O
custom	O
lightweight	O
networking	B-Architecture
protocols	O
designed	O
for	O
low-power	O
wireless	O
networks	O
.	O
</s>
<s>
The	O
IPv6	B-Protocol
stack	O
was	O
contributed	O
by	O
Cisco	O
and	O
was	O
,	O
when	O
released	O
,	O
the	O
smallest	O
IPv6	B-Protocol
stack	O
to	O
receive	O
the	O
IPv6	B-Protocol
Ready	O
certification	O
.	O
</s>
<s>
The	O
IPv6	B-Protocol
stack	O
also	O
contains	O
the	O
Routing	O
Protocol	O
for	O
Low	O
power	O
and	O
Lossy	O
Networks	O
(	O
RPL	O
)	O
routing	O
protocol	O
for	O
low-power	O
lossy	O
IPv6	B-Protocol
networks	O
and	O
the	O
6LoWPAN	B-Protocol
header	O
compression	O
and	O
adaptation	O
layer	O
for	O
IEEE	O
802.15.4	O
links	O
.	O
</s>
<s>
Rime	O
is	O
an	O
alternative	O
network	O
stack	O
,	O
for	O
use	O
when	O
the	O
overhead	O
of	O
the	O
IPv4	B-Protocol
or	O
IPv6	B-Protocol
stacks	O
is	O
prohibitive	O
.	O
</s>
<s>
Many	O
Contiki	B-Operating_System
systems	O
are	O
severely	O
power-constrained	O
.	O
</s>
<s>
Contiki	B-Operating_System
provides	O
a	O
set	O
of	O
mechanisms	O
to	O
reduce	O
the	O
power	O
consumption	O
of	O
systems	O
on	O
which	O
it	O
runs	O
.	O
</s>
<s>
The	O
Contiki	B-Operating_System
system	O
includes	O
a	O
sensor	O
simulator	O
called	O
Cooja	O
,	O
which	O
simulates	O
of	O
Contiki	B-Operating_System
nodes	O
.	O
</s>
<s>
The	O
nodes	O
belong	O
to	O
one	O
of	O
the	O
three	O
following	O
classes	O
:	O
a	O
)	O
emulated	O
Cooja	O
nodes	O
,	O
b	O
)	O
Contiki	B-Operating_System
code	O
compiled	O
and	O
executed	O
on	O
the	O
simulation	O
host	O
,	O
or	O
c	O
)	O
Java	O
nodes	O
,	O
where	O
the	O
behavior	O
of	O
the	O
node	O
must	O
be	O
reimplemented	O
as	O
a	O
Java	O
class	O
.	O
</s>
<s>
Emulated	O
nodes	O
can	O
also	O
be	O
used	O
to	O
include	O
non-Contiki	O
nodes	O
in	O
a	O
simulated	O
network	O
.	O
</s>
<s>
In	O
Contiki	B-Operating_System
2.6	O
,	O
platforms	O
with	O
the	O
TI	B-Architecture
MSP430	I-Architecture
and	O
Atmel	B-Architecture
AVR	I-Architecture
microcontrollers	O
can	O
be	O
emulated	O
.	O
</s>
<s>
To	O
run	O
efficiently	O
on	O
small-memory	O
systems	O
,	O
the	O
Contiki	B-Operating_System
programming	O
model	O
is	O
based	O
on	O
protothreads	B-Operating_System
.	O
</s>
<s>
A	O
protothread	B-Operating_System
is	O
a	O
memory-efficient	O
programming	O
abstraction	O
that	O
shares	O
features	O
of	O
both	O
multithreading	B-Operating_System
and	O
event-driven	B-Application
programming	I-Application
to	O
attain	O
a	O
low	O
memory	O
overhead	O
of	O
each	O
protothread	B-Operating_System
.	O
</s>
<s>
The	O
kernel	B-Operating_System
invokes	O
the	O
protothread	B-Operating_System
of	O
a	O
process	O
in	O
response	O
to	O
an	O
internal	O
or	O
external	O
event	O
.	O
</s>
<s>
Protothreads	B-Operating_System
are	O
cooperatively	O
scheduled	O
.	O
</s>
<s>
Thus	O
,	O
a	O
Contiki	B-Operating_System
process	O
must	O
always	O
explicitly	O
yield	O
control	O
back	O
to	O
the	O
kernel	B-Operating_System
at	O
regular	O
intervals	O
.	O
</s>
<s>
Contiki	B-Operating_System
processes	O
may	O
use	O
a	O
special	O
protothread	B-Operating_System
construct	O
to	O
block	O
waiting	O
for	O
events	O
while	O
yielding	O
control	O
to	O
the	O
kernel	B-Operating_System
between	O
each	O
event	O
invocation	O
.	O
</s>
<s>
Contiki	B-Operating_System
supports	O
per-process	O
optional	O
preemptive	B-Operating_System
multithreading	I-Operating_System
,	O
inter-process	B-Operating_System
communication	I-Operating_System
using	O
message	O
passing	O
through	O
events	O
,	O
as	O
well	O
as	O
an	O
optional	O
graphical	B-Application
user	I-Application
interface	I-Application
(	O
GUI	B-Application
)	O
subsystem	O
with	O
either	O
direct	O
graphic	O
support	O
for	O
locally	O
connected	O
terminals	O
or	O
networked	O
virtual	O
display	O
with	O
Virtual	B-Protocol
Network	I-Protocol
Computing	I-Protocol
(	O
VNC	B-Protocol
)	O
or	O
over	O
Telnet	B-Protocol
.	O
</s>
<s>
A	O
full	O
installation	O
of	O
Contiki	B-Operating_System
includes	O
the	O
following	O
features	O
:	O
</s>
<s>
Contiki	B-Operating_System
is	O
supported	O
by	O
popular	O
SSL/TLS	B-Protocol
libraries	O
such	O
as	O
wolfSSL	B-Protocol
,	O
which	O
includes	O
a	O
port	O
in	O
its	O
3.15.5	O
release	O
.	O
</s>
<s>
VIC-20	B-Device
,	O
</s>
