<s>
OpenTag	B-Device
is	O
a	O
DASH7	B-Device
protocol	B-Protocol
stack	I-Protocol
and	O
minimal	O
Real-Time	B-Operating_System
Operating	I-Operating_System
System	I-Operating_System
(	O
RTOS	B-Operating_System
)	O
,	O
written	O
in	O
the	O
C	B-Language
programming	I-Language
language	I-Language
.	O
</s>
<s>
It	O
is	O
designed	O
to	O
run	O
on	O
microcontrollers	B-Architecture
or	O
radio	O
Systems	B-Architecture
on	I-Architecture
a	I-Architecture
Chip	I-Architecture
(	O
SoC	O
)	O
.	O
</s>
<s>
OpenTag	B-Device
was	O
engineered	O
to	O
be	O
a	O
very	O
compact	O
software	O
package	O
.	O
</s>
<s>
OpenTag	B-Device
can	O
also	O
provide	O
all	O
functionality	O
required	O
for	O
any	O
type	O
of	O
DASH7	B-Device
Mode	O
2	O
device	O
,	O
rather	O
than	O
just	O
the	O
eponymous	O
“	O
tag	O
”	O
-type	O
endpoint	O
device	O
.	O
</s>
<s>
OpenTag	B-Device
implements	O
DASH7	B-Device
Mode	O
2	O
,	O
which	O
specifies	O
a	O
monolithic	B-Architecture
system	I-Architecture
encompassing	O
OSI	O
layers	O
one	O
through	O
six	O
,	O
part	O
of	O
layer	O
seven	O
,	O
as	O
well	O
as	O
the	O
application	B-Application
layer	I-Application
.	O
</s>
<s>
OpenTag	B-Device
is	O
designed	O
to	O
be	O
light	O
and	O
compact	O
,	O
as	O
it	O
is	O
targeted	O
to	O
run	O
on	O
resource-constrained	O
micro-controllers	B-Architecture
.	O
</s>
<s>
As	O
a	O
monolithic	B-Architecture
system	I-Architecture
,	O
it	O
does	O
not	O
implement	O
different	O
layers	O
of	O
the	O
OSI	O
model	O
in	O
a	O
way	O
that	O
will	O
enable	O
them	O
to	O
be	O
deployed	O
on	O
systems	O
that	O
differ	O
from	O
the	O
typical	O
,	O
and	O
nearly	O
universal	O
,	O
MCU+RF	O
transceiver	O
architecture	O
,	O
utilized	O
by	O
WSN	B-Architecture
and	O
M2M	O
nodes	O
.	O
</s>
<s>
However	O
,	O
the	O
OpenTag	B-Device
RTOS	B-Operating_System
employs	O
an	O
exokernel	B-Operating_System
architecture	O
(	O
as	O
of	O
version	O
0.4	O
)	O
,	O
so	O
a	O
monolithic	B-Operating_System
kernel	I-Operating_System
is	O
not	O
required	O
.	O
</s>
<s>
Applications	O
developed	O
for	O
OpenTag	B-Device
may	O
safely	O
reference	O
the	O
library	O
or	O
directly	O
access	O
the	O
hardware	O
,	O
as	O
befits	O
the	O
exokernel	B-Operating_System
design	O
model	O
.	O
</s>
<s>
It	O
has	O
a	O
lightweight	O
pre-emptive	O
multitasking	O
exokernel	B-Operating_System
RTOS	B-Operating_System
.	O
</s>
<s>
UDP	B-Protocol
&	O
SCTP	B-Protocol
adaptation	O
layers	O
.	O
</s>
<s>
It	O
uses	O
a	O
Wear-leveling	B-Application
,	O
Flash-based	O
lightweight	O
filesystem	B-Application
(	O
Veelite	O
)	O
.	O
</s>
<s>
It	O
has	O
an	O
internal	O
C-based	O
API	B-General_Concept
.	O
</s>
<s>
It	O
has	O
an	O
external	O
NDEF-based	O
messaging	O
API	B-General_Concept
for	O
client-server	B-Operating_System
interaction	O
.	O
</s>
<s>
OpenTag	B-Device
implements	O
a	O
multitasking	O
real-time	O
kernel	O
designed	O
specifically	O
to	O
implement	O
DASH7	B-Device
.	O
</s>
<s>
Thus	O
callbacks	O
in	O
OpenTag	B-Device
may	O
be	O
dynamic	O
(	O
assigned	O
during	O
runtime	O
)	O
,	O
or	O
they	O
may	O
be	O
static	O
,	O
which	O
requires	O
assignment	O
at	O
compile-time	O
but	O
reduces	O
overhead	O
.	O
</s>
<s>
As	O
OpenTag	B-Device
implements	O
an	O
exokernel	B-Operating_System
,	O
user	O
tasks	O
may	O
either	O
be	O
managed	O
entirely	O
by	O
the	O
kernel	O
,	O
they	O
may	O
be	O
managed	O
partly	O
by	O
the	O
kernel	O
and	O
partly	O
by	O
external	O
events	O
,	O
or	O
they	O
may	O
be	O
managed	O
entirely	O
by	O
external	O
events	O
.	O
</s>
<s>
Communication	O
between	O
tasks	O
and	O
the	O
kernel	O
is	O
accomplished	O
through	O
an	O
API	B-General_Concept
of	O
system	O
calls	O
and	O
a	O
message	O
pipe	O
interface	O
.	O
</s>
<s>
OpenTag	B-Device
's	O
external	O
API	B-General_Concept
uses	O
a	O
simplified	O
client-server	B-Operating_System
model	I-Operating_System
and	O
NDEF	O
for	O
data	O
wrapping	O
.	O
</s>
<s>
The	O
NDEF	O
wrapper	O
is	O
particularly	O
used	O
for	O
wireline	O
communication	O
between	O
client	O
and	O
server	O
,	O
where	O
the	O
client	O
is	O
typically	O
a	O
human-interface	O
device	O
and	O
the	O
server	O
is	O
the	O
OpenTag	B-Device
SoC	O
.	O
</s>
<s>
The	O
internal	O
API	B-General_Concept
is	O
exposed	O
in	O
a	O
1:1	O
manner	O
with	O
the	O
external	O
API	B-General_Concept
,	O
permitting	O
the	O
client	O
to	O
act	O
much	O
like	O
an	O
external	O
process	O
of	O
the	O
OpenTag	B-Device
kernel	O
.	O
</s>
<s>
At	O
the	O
time	O
of	O
writing	O
,	O
most	O
OpenTag	B-Device
hardware	O
is	O
implemented	O
on	O
the	O
Texas	O
Instruments	O
CC430	B-Architecture
or	I-Architecture
MSP430	I-Architecture
devices	O
,	O
which	O
are	O
endorsed	O
for	O
use	O
with	O
OpenTag	B-Device
.	O
</s>
<s>
Current	O
OpenTag	B-Device
source	O
trees	O
support	O
many	O
other	O
MCUs	O
and	O
RF	O
transceivers	O
,	O
however	O
,	O
such	O
as	O
various	O
types	O
of	O
STM32	O
,	O
CC11xx	O
,	O
and	O
Semtech	O
SX12xx	O
components	O
.	O
</s>
