<s>
XtratuM	B-Application
is	O
a	O
bare-metal	O
hypervisor	B-Operating_System
specially	O
designed	O
for	O
embedded	B-Architecture
real-time	B-General_Concept
systems	I-General_Concept
available	O
for	O
the	O
instruction	B-General_Concept
sets	I-General_Concept
LEON2/3/4	B-General_Concept
(	O
SPARC	B-Architecture
v8	I-Architecture
)	O
,	O
ARM	B-Architecture
v7	O
and	O
V8	O
processors	O
(	O
TMS570	O
,	O
R5	O
,	O
A9	O
,	O
A52	O
,	O
A53	O
)	O
and	O
RISC	O
V	O
processor	O
.	O
</s>
<s>
XtratuM	B-Application
was	O
released	O
as	O
free	B-License
and	I-License
open-source	I-License
software	I-License
,	O
subject	O
to	O
the	O
requirements	O
of	O
the	O
GNU	B-License
General	I-License
Public	I-License
License	I-License
(	O
GPL	B-License
)	O
,	O
version	O
2	O
or	O
any	O
later	O
.	O
</s>
<s>
A	O
new	O
version	O
of	O
XtratuM	B-Application
from	O
scratch	O
(	O
XtratuM	B-Application
New	O
Generation	O
XNG	O
)	O
is	O
commercialized	O
by	O
under	O
a	O
proprietary	O
license	O
.	O
</s>
<s>
XtratuM	B-Application
is	O
a	O
hypervisor	B-Operating_System
designed	O
for	O
embedded	B-Architecture
systems	I-Architecture
to	O
meet	O
safety	O
critical	O
real-time	B-General_Concept
requirements	O
.	O
</s>
<s>
It	O
provides	O
a	O
framework	O
to	O
run	O
several	O
operating	B-General_Concept
systems	I-General_Concept
(	O
or	O
real-time	B-General_Concept
executives	O
)	O
in	O
a	O
robust	O
partitioned	O
environment	O
.	O
</s>
<s>
XtratuM	B-Application
can	O
be	O
used	O
to	O
build	O
a	O
MILS	B-Operating_System
(	O
Multiple	B-Operating_System
Independent	I-Operating_System
Levels	I-Operating_System
of	I-Operating_System
Security	I-Operating_System
)	O
architecture	O
.	O
</s>
<s>
The	O
name	O
XtratuM	B-Application
derives	O
from	O
the	O
word	O
stratum	O
.	O
</s>
<s>
XtratuM	B-Application
would	O
be	O
the	O
first	O
layer	O
of	O
software	O
(	O
the	O
one	O
closest	O
to	O
the	O
hardware	O
)	O
,	O
which	O
provides	O
a	O
solid	O
basis	O
for	O
the	O
rest	O
of	O
the	O
system	O
.	O
</s>
<s>
The	O
result	O
of	O
this	O
is	O
XtratuM	B-Application
2.0	O
which	O
is	O
type	O
1	O
hypervisor	B-Operating_System
that	O
uses	O
para-virtualization	O
.	O
</s>
<s>
native	O
system	O
is	O
a	O
simple	O
task	O
:	O
replace	O
some	O
parts	O
of	O
the	O
operating	B-General_Concept
system	I-General_Concept
HAL	O
with	O
the	O
corresponding	O
hypercalls	B-Operating_System
.	O
</s>
<s>
The	O
design	O
of	O
a	O
hypervisor	B-Operating_System
for	O
critical	O
real-time	B-General_Concept
embedded	B-Architecture
systems	I-Architecture
follows	O
these	O
criteria	O
:	O
</s>
<s>
Basic	O
resource	O
virtualization	O
:	O
clock	O
and	O
timers	O
,	O
interrupts	O
,	O
memory	O
,	O
CPU	B-Device
and	O
special	O
devices	O
.	O
</s>
<s>
Real-time	B-General_Concept
scheduling	O
policy	O
for	O
partition	O
scheduling	O
.	O
</s>
<s>
Deterministic	O
hypercalls	B-Operating_System
(	O
hypervisor	B-Operating_System
system	O
calls	O
)	O
.	O
</s>
<s>
In	O
the	O
case	O
of	O
embedded	B-Architecture
systems	I-Architecture
,	O
particularly	O
avionics	O
systems	O
,	O
the	O
ARINC	O
653	O
standard	O
defines	O
a	O
partitioning	O
scheme	O
.	O
</s>
<s>
Although	O
this	O
standard	O
was	O
not	O
designed	O
to	O
describe	O
how	O
a	O
hypervisor	B-Operating_System
must	O
operate	O
,	O
some	O
parts	O
of	O
the	O
model	O
are	O
quite	O
close	O
to	O
the	O
functionality	O
provided	O
by	O
a	O
hypervisor	B-Operating_System
.	O
</s>
<s>
The	O
XtratuM	B-Application
API	O
and	O
internal	O
operations	O
resemble	O
the	O
ARINC	O
653	O
standard	O
.	O
</s>
<s>
XtratuM	B-Application
is	O
not	O
an	O
ARINC	O
653	O
compliant	O
system	O
.	O
</s>
<s>
The	O
standard	O
relies	O
on	O
the	O
idea	O
of	O
a	O
separation	B-Operating_System
kernel	I-Operating_System
defining	O
both	O
the	O
API	O
and	O
operations	O
of	O
the	O
partitions	O
and	O
also	O
how	O
the	O
threads	O
or	O
processes	O
are	O
managed	O
inside	O
each	O
partition	O
.	O
</s>
<s>
XtratuM	B-Application
hypervisor	B-Operating_System
supports	O
the	O
LEON	B-General_Concept
2/LEON	O
3/LEON	O
4	O
(	O
SPARCv8	O
)	O
and	O
Cortex	O
R4/Cortex	O
R5/Cortex	O
A9	O
(	O
ARMv7	O
)	O
architectures	O
.	O
</s>
<s>
XtratuM	B-Application
support	O
as	O
execution	O
environments	O
:	O
</s>
