<s>
FreeRTOS	B-Operating_System
is	O
a	O
real-time	B-Operating_System
operating	I-Operating_System
system	I-Operating_System
kernel	B-Operating_System
for	O
embedded	B-Architecture
devices	I-Architecture
that	O
has	O
been	O
ported	O
to	O
35	O
microcontroller	B-Architecture
platforms	O
.	O
</s>
<s>
It	O
is	O
distributed	O
under	O
the	B-License
MIT	I-License
License	I-License
.	O
</s>
<s>
The	O
FreeRTOS	B-Operating_System
kernel	B-Operating_System
was	O
originally	O
developed	O
by	O
Richard	O
Barry	O
around	O
2003	O
,	O
and	O
was	O
later	O
developed	O
and	O
maintained	O
by	O
Barry	O
's	O
company	O
,	O
Real	O
Time	O
Engineers	O
Ltd	O
.	O
</s>
<s>
In	O
2017	O
,	O
the	O
firm	O
passed	O
stewardship	O
of	O
the	O
FreeRTOS	B-Operating_System
project	O
to	O
Amazon	B-Application
Web	I-Application
Services	I-Application
(	O
AWS	B-Application
)	O
.	O
</s>
<s>
Barry	O
continues	O
to	O
work	O
on	O
FreeRTOS	B-Operating_System
as	O
part	O
of	O
an	O
AWS	B-Application
team	O
.	O
</s>
<s>
FreeRTOS	B-Operating_System
is	O
designed	O
to	O
be	O
small	O
and	O
simple	O
.	O
</s>
<s>
It	O
is	O
mostly	O
written	O
in	O
the	O
C	B-Language
programming	I-Language
language	I-Language
to	O
make	O
it	O
easy	O
to	O
port	O
and	O
maintain	O
.	O
</s>
<s>
It	O
also	O
comprises	O
a	O
few	O
assembly	B-Language
language	I-Language
functions	O
where	O
needed	O
,	O
mostly	O
in	O
architecture-specific	O
scheduler	O
routines	O
.	O
</s>
<s>
FreeRTOS	B-Operating_System
provides	O
methods	O
for	O
multiple	O
threads	B-Operating_System
or	O
tasks	B-General_Concept
,	O
mutexes	B-Operating_System
,	O
semaphores	B-Operating_System
and	O
software	O
timers	O
.	O
</s>
<s>
A	O
tickless	B-Operating_System
mode	O
is	O
provided	O
for	O
low	O
power	O
applications	O
.	O
</s>
<s>
Thread	B-Operating_System
priorities	O
are	O
supported	O
.	O
</s>
<s>
FreeRTOS	B-Operating_System
applications	O
can	O
be	O
statically	O
allocated	O
,	O
but	O
objects	O
can	O
also	O
be	O
dynamically	O
allocated	O
with	O
five	O
schemes	O
of	O
memory	B-General_Concept
management	I-General_Concept
(	O
allocation	O
)	O
:	O
</s>
<s>
a	O
more	O
complex	O
but	O
fast	O
allocate	O
and	O
free	O
algorithm	O
with	O
memory	B-General_Concept
coalescence	I-General_Concept
;	O
</s>
<s>
an	O
alternative	O
to	O
the	O
more	O
complex	O
scheme	O
that	O
includes	O
memory	B-General_Concept
coalescence	I-General_Concept
that	O
allows	O
a	O
heap	O
to	O
be	O
broken	O
across	O
multiple	O
memory	O
areas	O
.	O
</s>
<s>
and	O
C	B-Language
library	O
allocate	O
and	O
free	O
with	O
some	O
mutual	O
exclusion	O
protection	O
.	O
</s>
<s>
RTOSes	O
typically	O
do	O
not	O
have	O
the	O
more	O
advanced	O
features	O
that	O
are	O
found	O
in	O
operating	B-General_Concept
systems	I-General_Concept
like	O
Linux	B-Application
and	O
Microsoft	B-Application
Windows	I-Application
,	O
such	O
as	O
device	B-Application
drivers	I-Application
,	O
advanced	O
memory	B-General_Concept
management	I-General_Concept
,	O
and	O
user	O
accounts	O
.	O
</s>
<s>
FreeRTOS	B-Operating_System
can	O
be	O
thought	O
of	O
as	O
a	O
thread	B-Operating_System
library	O
rather	O
than	O
an	O
operating	B-General_Concept
system	I-General_Concept
,	O
although	O
command	O
line	O
interface	O
and	O
POSIX-like	O
input/output	B-General_Concept
(	O
I/O	B-General_Concept
)	O
abstraction	O
are	O
available	O
.	O
</s>
<s>
FreeRTOS	B-Operating_System
implements	O
multiple	O
threads	B-Operating_System
by	O
having	O
the	O
host	O
program	O
call	O
a	O
thread	B-Operating_System
tick	O
method	O
at	O
regular	O
short	O
intervals	O
.	O
</s>
<s>
The	O
thread	B-Operating_System
tick	O
method	O
switches	O
tasks	B-General_Concept
depending	O
on	O
priority	O
and	O
a	O
round-robin	B-Algorithm
scheduling	I-Algorithm
scheme	O
.	O
</s>
<s>
The	O
project	O
website	O
provides	O
documentation	O
and	O
RTOS	B-Operating_System
tutorials	O
,	O
and	O
details	O
of	O
the	O
RTOS	B-Operating_System
design	O
.	O
</s>
<s>
Tools	O
such	O
as	O
Tracealyzer	O
,	O
a	O
commercial	O
tool	O
by	O
FreeRTOS	B-Operating_System
partner	O
Percepio	O
,	O
can	O
thereby	O
record	O
and	O
visualize	O
the	O
runtime	B-Library
behavior	O
of	O
FreeRTOS-based	O
systems	O
for	O
debugging	O
and	O
verification	O
.	O
</s>
<s>
This	O
includes	O
task	B-General_Concept
scheduling	O
and	O
kernel	B-Operating_System
calls	O
for	O
semaphore	B-Operating_System
and	O
queue	O
operations	O
.	O
</s>
<s>
Amazon	B-Application
provides	O
an	O
extension	O
of	O
FreeRTOS	B-Operating_System
,	O
referred	O
to	O
as	O
a:FreeRTOS	O
.	O
</s>
<s>
This	O
is	O
FreeRTOS	B-Operating_System
with	O
libraries	O
for	O
Internet	B-Operating_System
of	I-Operating_System
things	I-Operating_System
(	O
IoT	B-Operating_System
)	O
support	O
,	O
specifically	O
for	O
Amazon	B-Application
Web	I-Application
Services	I-Application
.	O
</s>
<s>
Since	O
version	O
10.0.0	O
in	O
2017	O
,	O
Amazon	B-Application
has	O
taken	O
stewardship	O
of	O
the	O
FreeRTOS	B-Operating_System
code	O
,	O
including	O
any	O
updates	O
to	O
the	O
original	O
kernel	B-Operating_System
.	O
</s>
<s>
SAFERTOS	O
was	O
developed	O
as	O
a	O
complementary	O
version	O
of	O
FreeRTOS	B-Operating_System
,	O
with	O
common	O
functions	O
,	O
but	O
designed	O
for	O
safety-critical	O
implementation	O
.	O
</s>
<s>
FreeRTOS	B-Operating_System
was	O
subject	O
to	O
hazard	O
and	O
operability	O
study	O
(	O
HAZOP	O
)	O
,	O
and	O
weaknesses	O
were	O
identified	O
and	O
resolved	O
.	O
</s>
<s>
SAFERTOS	O
was	O
developed	O
by	O
Wittenstein	O
High	O
Integrity	O
Systems	O
,	O
in	O
partnership	O
with	O
Real	O
Time	O
Engineers	O
Ltd	O
,	O
primary	O
developer	O
of	O
the	O
FreeRTOS	B-Operating_System
project	O
.	O
</s>
<s>
Both	O
SAFERTOS	O
and	O
FreeRTOS	B-Operating_System
share	O
the	O
same	O
scheduling	O
algorithm	O
,	O
have	O
similar	O
application	O
programming	O
interfaces	O
(	O
APIs	B-General_Concept
)	O
,	O
and	O
are	O
otherwise	O
very	O
similar	O
,	O
but	O
they	O
were	O
developed	O
with	O
differing	O
objectives	O
.	O
</s>
<s>
SAFERTOS	O
was	O
developed	O
solely	O
in	O
the	O
C	B-Language
language	I-Language
to	O
meet	O
requirements	O
for	O
certification	O
to	O
IEC61508	O
.	O
</s>
<s>
SAFERTOS	O
can	O
reside	O
solely	O
in	O
the	O
on-chip	O
read-only	B-Device
memory	I-Device
(	O
ROM	B-Device
)	O
of	O
a	O
microcontroller	B-Architecture
for	O
standards	O
compliance	O
.	O
</s>
<s>
This	O
means	O
certifying	O
a	O
system	O
needs	O
no	O
retesting	O
of	O
the	O
kernel	B-Operating_System
portion	O
of	O
a	O
design	O
.	O
</s>
<s>
SAFERTOS	O
is	O
included	O
in	O
the	O
ROM	B-Device
of	O
some	O
Stellaris	O
Microcontrollers	B-Architecture
from	O
Texas	O
Instruments	O
.	O
</s>
<s>
In	O
this	O
usage	O
scenario	O
,	O
a	O
C	B-Language
header	O
file	O
is	O
used	O
to	O
map	O
SAFERTOS	O
API	B-General_Concept
functions	O
to	O
their	O
location	O
in	O
read-only	B-Device
memory	I-Device
.	O
</s>
<s>
OPENRTOS	O
is	O
a	O
commercially-licensed	O
version	O
of	O
Amazon	B-Application
FreeRTOS	B-Operating_System
,	O
sold	O
by	O
Wittenstein	O
High	O
Integrity	O
Systems	O
.	O
</s>
<s>
This	O
product	O
provides	O
support	O
and	O
allows	O
companies	O
to	O
use	O
the	O
Amazon	B-Application
FreeRTOS	B-Operating_System
kernel	B-Operating_System
and	O
libraries	O
without	O
the	O
a:FreeRTOS	O
MIT	B-License
license	I-License
.	O
</s>
