<s>
The	O
RapidIO	B-General_Concept
architecture	O
is	O
a	O
high-performance	O
packet-switched	B-Protocol
electrical	B-Protocol
connection	I-Protocol
technology	O
.	O
</s>
<s>
RapidIO	B-General_Concept
supports	O
messaging	O
,	O
read/write	O
and	O
cache	B-General_Concept
coherency	I-General_Concept
semantics	O
.	O
</s>
<s>
Based	O
on	O
industry-standard	O
electrical	O
specifications	O
such	O
as	O
those	O
for	O
Ethernet	O
,	O
RapidIO	B-General_Concept
can	O
be	O
used	O
as	O
a	O
chip-to-chip	O
,	O
board-to-board	O
,	O
and	O
chassis-to-chassis	O
interconnect	B-General_Concept
.	O
</s>
<s>
The	O
RapidIO	B-General_Concept
protocol	O
was	O
originally	O
designed	O
by	O
Mercury	B-Application
Computer	I-Application
Systems	I-Application
and	O
Motorola	O
(	O
Freescale	O
)	O
as	O
a	O
replacement	O
for	O
Mercury	O
's	O
RACEway	O
proprietary	O
bus	O
and	O
Freescale	O
's	O
PowerPC	O
bus	O
.	O
</s>
<s>
The	O
RapidIO	B-General_Concept
Trade	O
Association	O
was	O
formed	O
in	O
February	O
2000	O
,	O
and	O
included	O
telecommunications	O
and	O
storage	O
OEMs	O
as	O
well	O
as	O
FPGA	O
,	O
processor	O
,	O
and	O
switch	O
companies	O
.	O
</s>
<s>
The	O
RapidIO	B-General_Concept
specification	O
revision	O
1.1	O
(	O
3xN	O
Gen1	O
)	O
,	O
released	O
in	O
March	O
2001	O
,	O
defined	O
a	O
wide	O
,	O
parallel	O
bus	O
.	O
</s>
<s>
The	O
RapidIO	B-General_Concept
specification	O
revision	O
1.2	O
,	O
released	O
in	O
June	O
2002	O
,	O
defined	O
a	O
serial	O
interconnect	B-General_Concept
based	O
on	O
the	O
XAUI	B-Protocol
physical	O
layer	O
.	O
</s>
<s>
The	O
RapidIO	B-General_Concept
specification	O
revision	O
1.3	O
was	O
released	O
in	O
June	O
2005	O
.	O
</s>
<s>
The	O
RapidIO	B-General_Concept
specification	O
revision	O
2.0	O
(	O
6xN	O
Gen2	O
)	O
,	O
was	O
released	O
in	O
March	O
2008	O
,	O
added	O
more	O
port	O
widths	O
(	O
2×	O
,	O
8×	O
,	O
and	O
16×	O
)	O
and	O
increased	O
the	O
maximum	O
lane	O
speed	O
to	O
6.25GBd	O
/	O
5Gbit/s	O
.	O
</s>
<s>
The	O
RapidIO	B-General_Concept
specification	O
revision	O
2.1	O
was	O
released	O
in	O
September	O
2009	O
.	O
</s>
<s>
The	O
RapidIO	B-General_Concept
specification	O
revision	O
2.2	O
was	O
released	O
in	O
May	O
2011	O
.	O
</s>
<s>
The	O
RapidIO	B-General_Concept
specification	O
revision	O
3.0	O
(	O
10xN	O
Gen3	O
)	O
,	O
was	O
released	O
in	O
October	O
2013	O
,	O
has	O
the	O
following	O
changes	O
and	O
improvements	O
compared	O
to	O
the	O
2.x	O
specifications	O
:	O
</s>
<s>
The	O
RapidIO	B-General_Concept
specification	O
revision	O
3.1	O
,	O
was	O
released	O
in	O
October	O
2014	O
,	O
was	O
developed	O
through	O
a	O
collaboration	O
between	O
the	O
RapidIO	B-General_Concept
Trade	O
Association	O
and	O
NGSIS	O
.	O
</s>
<s>
Space	O
device	O
profiles	O
for	O
endpoints	O
and	O
switches	O
,	O
which	O
define	O
what	O
it	O
means	O
to	O
be	O
a	O
space-compliant	O
RapidIO	B-General_Concept
device	O
.	O
</s>
<s>
The	O
RapidIO	B-General_Concept
specification	O
revision	O
3.2	O
was	O
released	O
in	O
February	O
2016	O
.	O
</s>
<s>
The	O
RapidIO	B-General_Concept
specification	O
revision	O
4.0	O
(	O
25xN	O
Gen4	O
)	O
was	O
released	O
in	O
June	O
2016	O
.	O
has	O
the	O
following	O
changes	O
and	O
improvements	O
compared	O
to	O
the	O
3.x	O
specifications	O
:	O
</s>
<s>
The	O
RapidIO	B-General_Concept
specification	O
revision	O
4.1	O
was	O
released	O
in	O
July	O
2017	O
.	O
</s>
<s>
RapidIO	B-General_Concept
fabrics	O
are	O
used	O
in	O
cellular	O
infrastructure	O
3G	O
,	O
4G	O
and	O
LTE	O
networks	O
with	O
millions	O
of	O
RapidIO	B-General_Concept
ports	O
shipped	O
into	O
wireless	O
base	O
stations	O
worldwide	O
.	O
</s>
<s>
RapidIO	B-General_Concept
fabrics	O
were	O
originally	O
designed	O
to	O
support	O
connecting	O
different	O
types	O
of	O
processors	O
from	O
different	O
manufacturers	O
together	O
in	O
a	O
single	O
system	O
.	O
</s>
<s>
This	O
flexibility	O
has	O
driven	O
the	O
widespread	O
use	O
of	O
RapidIO	B-General_Concept
in	O
wireless	O
infrastructure	O
equipment	O
where	O
there	O
is	O
a	O
need	O
to	O
combine	O
heterogeneous	O
,	O
DSP	O
,	O
FPGA	O
and	O
communication	O
processors	O
together	O
in	O
a	O
tightly	O
coupled	O
system	O
with	O
low	O
latency	O
and	O
high	O
reliability	O
.	O
</s>
<s>
Data	O
center	O
and	O
HPC	O
analytics	O
systems	O
have	O
been	O
deployed	O
using	O
a	O
RapidIO	B-General_Concept
2D	O
Torus	O
Mesh	O
Fabric	O
,	O
that	O
provides	O
a	O
high	O
speed	O
general	O
purpose	O
interface	O
among	O
the	O
system	O
cartridges	O
for	O
applications	O
that	O
benefit	O
from	O
high	O
bandwidth	O
,	O
low	O
latency	O
node-to-node	O
communication	O
.	O
</s>
<s>
The	O
RapidIO	B-General_Concept
2D	O
Torus	O
unified	O
fabric	O
is	O
routed	O
as	O
a	O
torus	O
ring	O
configuration	O
connecting	O
up	O
to	O
45	O
server	O
cartridges	O
capable	O
of	O
providing	O
5Gbs	O
per	O
lane	O
connections	O
in	O
each	O
direction	O
to	O
its	O
north	O
,	O
south	O
,	O
east	O
and	O
west	O
neighbors	O
.	O
</s>
<s>
Also	O
,	O
using	O
an	O
open	O
modular	O
data	O
center	O
and	O
compute	O
platform	O
,	O
a	O
heterogeneous	O
HPC	O
system	O
has	O
showcased	O
the	O
low	O
latency	O
attribute	O
of	O
RapidIO	B-General_Concept
to	O
enable	O
real-time	O
analytics	O
.	O
</s>
<s>
In	O
March	O
2015	O
a	O
top-of-rack	O
switch	O
was	O
announced	O
to	O
drive	O
RapidIO	B-General_Concept
into	O
mainstream	O
data	O
center	O
applications	O
.	O
</s>
<s>
The	O
interconnect	B-General_Concept
or	O
"	O
bus	O
"	O
is	O
one	O
of	O
the	O
critical	O
technologies	O
in	O
the	O
design	O
and	O
development	O
of	O
spacecraft	O
avionic	O
systems	O
that	O
dictates	O
its	O
architecture	O
and	O
level	O
of	O
complexity	O
.	O
</s>
<s>
In	O
2012	O
,	O
RapidIO	B-General_Concept
was	O
selected	O
by	O
the	O
Next	O
Generation	O
Spacecraft	O
Interconnect	B-General_Concept
Standard	O
(	O
NGSIS	O
)	O
working	O
group	O
to	O
serve	O
as	O
the	O
foundation	O
for	O
standard	O
communication	O
interconnects	B-General_Concept
to	O
be	O
used	O
in	O
spacecraft	O
.	O
</s>
<s>
The	O
NGSIS	O
is	O
an	O
umbrella	O
standards	O
effort	O
that	O
includes	O
RapidIO	B-General_Concept
Version	O
3.1	O
development	O
,	O
and	O
a	O
box	O
level	O
hardware	O
standards	O
effort	O
under	O
VITA	O
78	O
called	O
SpaceVPX	O
or	O
High	O
ReliabilityVPX	O
.	O
</s>
<s>
The	O
NGSIS	O
requirements	O
committee	O
developed	O
extensive	O
requirements	O
criteria	O
with	O
47	O
different	O
elements	O
for	O
the	O
NGSIS	O
interconnect	B-General_Concept
.	O
</s>
<s>
Independent	O
trade	O
study	O
results	O
by	O
NGSIS	O
member	O
companies	O
demonstrated	O
the	O
superiority	O
of	O
RapidIO	B-General_Concept
over	O
other	O
existing	O
commercial	O
protocols	O
,	O
such	O
as	O
InfiniBand	O
,	O
Fibre	O
Channel	O
,	O
and	O
10G	O
Ethernet	O
.	O
</s>
<s>
As	O
a	O
result	O
,	O
the	O
group	O
decided	O
that	O
RapidIO	B-General_Concept
offered	O
the	O
best	O
overall	O
interconnect	B-General_Concept
for	O
the	O
needs	O
of	O
next-generation	O
spacecraft	O
.	O
</s>
<s>
The	O
RapidIO	B-General_Concept
roadmap	O
aligns	O
with	O
Ethernet	O
PHY	O
development	O
.	O
</s>
<s>
RapidIO	B-General_Concept
specifications	O
for	O
50GBd	O
and	O
higher	O
links	O
are	O
under	O
investigation	O
.	O
</s>
<s>
Link	O
Partner	O
One	O
end	O
of	O
a	O
RapidIO	B-General_Concept
link	O
.	O
</s>
<s>
Endpoint	O
A	O
device	O
that	O
can	O
originate	O
and/or	O
terminate	O
RapidIO	B-General_Concept
packets	O
.	O
</s>
<s>
Switch	O
A	O
device	O
that	O
can	O
route	O
RapidIO	B-General_Concept
packets	O
.	O
</s>
<s>
The	O
RapidIO	B-General_Concept
protocol	O
is	O
defined	O
in	O
a	O
3-layered	O
specification	O
:	O
</s>
<s>
The	O
RapidIO	B-General_Concept
electrical	O
specifications	O
are	O
based	O
on	O
industry-standard	O
Ethernet	O
and	O
Optical	O
Interconnect	B-General_Concept
Forum	O
standards	O
:	O
</s>
<s>
The	O
RapidIO	B-General_Concept
PCS/PMA	O
layer	O
supports	O
two	O
forms	O
of	O
encoding/framing	O
:	O
</s>
<s>
Every	O
RapidIO	B-General_Concept
processing	O
element	O
transmits	O
and	O
receives	O
three	O
kinds	O
of	O
information	O
:	O
Packets	O
,	O
control	O
symbols	O
,	O
and	O
an	O
idle	O
sequence	O
.	O
</s>
<s>
The	O
physical	O
layer	O
contribution	O
to	O
RapidIO	B-General_Concept
packets	O
is	O
a	O
2-byte	O
header	O
at	O
the	O
beginning	O
of	O
each	O
packet	O
that	O
includes	O
the	O
ackID	O
and	O
physical	O
priority	O
,	O
and	O
a	O
final	O
2-byte	O
CRC	O
value	O
to	O
check	O
the	O
integrity	O
of	O
the	O
packet	O
.	O
</s>
<s>
RapidIO	B-General_Concept
control	O
symbols	O
can	O
be	O
sent	O
at	O
any	O
time	O
,	O
including	O
within	O
a	O
packet	O
.	O
</s>
<s>
This	O
gives	O
RapidIO	B-General_Concept
the	O
lowest	O
possible	O
in-band	O
control	O
path	O
latency	O
,	O
enabling	O
the	O
protocol	O
to	O
achieve	O
high	O
throughput	O
with	O
smaller	O
buffers	O
than	O
other	O
protocols	O
.	O
</s>
<s>
Control	O
symbols	O
are	O
used	O
to	O
delimit	O
packets	O
(	O
Start	O
of	O
Packet	O
,	O
End	O
of	O
Packet	O
,	O
Stomp	O
)	O
,	O
to	O
acknowledge	O
packets	O
(	O
Packet	O
Acknowledge	O
,	O
Packet	O
Not	O
Acknowledged	O
)	O
,	O
reset	O
(	O
Reset	O
Device	O
,	O
Reset	O
Port	O
)	O
and	O
to	O
distribute	O
events	O
within	O
the	O
RapidIO	B-General_Concept
system	O
(	O
Multicast	O
Event	O
Control	O
Symbol	O
)	O
.	O
</s>
<s>
Every	O
RapidIO	B-General_Concept
endpoint	O
is	O
uniquely	O
identified	O
by	O
a	O
Device	O
Identifier	O
(	O
deviceID	O
)	O
.	O
</s>
<s>
Each	O
RapidIO	B-General_Concept
packet	O
contains	O
two	O
device	O
IDs	O
.	O
</s>
<s>
When	O
an	O
endpoint	O
receives	O
a	O
RapidIO	B-General_Concept
request	O
packet	O
that	O
requires	O
a	O
response	O
,	O
the	O
response	O
packet	O
is	O
composed	O
by	O
swapping	O
the	O
srcID	O
and	O
destID	O
of	O
the	O
request	O
.	O
</s>
<s>
RapidIO	B-General_Concept
switches	O
use	O
the	O
destID	O
of	O
received	O
packets	O
to	O
determine	O
the	O
output	O
port	O
or	O
ports	O
that	O
should	O
forward	O
the	O
packet	O
.	O
</s>
<s>
RapidIO	B-General_Concept
switches	O
support	O
a	O
standard	O
programming	O
model	O
for	O
the	O
routing	O
table	O
,	O
which	O
simplifies	O
system	O
control	O
.	O
</s>
<s>
The	O
RapidIO	B-General_Concept
transport	O
layer	O
supports	O
any	O
network	O
topology	O
,	O
from	O
simple	O
trees	O
and	O
meshes	O
to	O
n-dimensional	O
hypercubes	B-Operating_System
,	O
multi-dimensional	O
toroids	O
,	O
and	O
more	O
esoteric	O
architectures	O
such	O
as	O
entangled	O
networks	O
.	O
</s>
<s>
The	O
RapidIO	B-General_Concept
transport	O
layer	O
enables	O
hardware	O
virtualization	O
(	O
for	O
example	O
,	O
a	O
RapidIO	B-General_Concept
endpoint	O
can	O
support	O
multiple	O
device	O
IDs	O
)	O
.	O
</s>
<s>
The	O
RapidIO	B-General_Concept
logical	O
layer	O
is	O
composed	O
of	O
several	O
specifications	O
,	O
each	O
providing	O
packet	O
formats	O
and	O
protocols	O
for	O
different	O
transaction	O
semantics	O
.	O
</s>
<s>
The	O
Globally	O
Shared	O
Memory	O
specification	O
defines	O
packet	O
formats	O
and	O
protocols	O
for	O
operating	O
a	O
cache	O
coherent	O
shared	O
memory	O
system	O
over	O
a	O
RapidIO	B-General_Concept
network	O
.	O
</s>
<s>
The	O
RapidIO	B-General_Concept
system	O
initialization	O
specification	O
supports	O
system	O
initialization	O
when	O
system	O
topology	O
is	O
unknown	O
or	O
dynamic	O
.	O
</s>
<s>
Each	O
system	O
host	O
recursively	O
enumerates	O
the	O
RapidIO	B-General_Concept
fabric	O
,	O
seizing	O
ownership	O
of	O
devices	O
,	O
allocating	O
device	O
IDs	O
to	O
endpoints	O
and	O
updating	O
switch	O
routing	O
tables	O
.	O
</s>
<s>
System	O
enumeration	O
is	O
supported	O
in	O
Linux	O
by	O
the	O
RapidIO	B-General_Concept
subsystem	O
.	O
</s>
<s>
RapidIO	B-General_Concept
supports	O
high	O
availability	O
,	O
fault	O
tolerant	O
system	O
design	O
,	O
including	O
hot	O
swap	O
.	O
</s>
<s>
The	O
RapidIO	B-General_Concept
specification	O
does	O
not	O
discuss	O
the	O
subjects	O
of	O
form	O
factors	O
and	O
connectors	O
,	O
leaving	O
this	O
to	O
specific	O
application-focussed	O
communities	O
.	O
</s>
<s>
RapidIO	B-General_Concept
is	O
supported	O
by	O
the	O
following	O
form	O
factors	O
:	O
</s>
<s>
Processor-agnostic	O
RapidIO	B-General_Concept
support	O
is	O
found	O
in	O
the	O
Linux	O
kernel	O
.	O
</s>
<s>
The	O
RapidIO	B-General_Concept
interconnect	B-General_Concept
is	O
used	O
extensively	O
in	O
the	O
following	O
applications	O
:	O
</s>
<s>
RapidIO	B-General_Concept
is	O
expanding	O
into	O
supercomputing	O
,	O
server	O
,	O
and	O
storage	O
applications	O
.	O
</s>
<s>
Unlike	O
RapidIO	B-General_Concept
,	O
PCIe	O
is	O
not	O
optimized	O
for	O
peer-to-peer	O
multi	O
processor	O
networks	O
.	O
</s>
<s>
Another	O
alternative	O
interconnect	B-General_Concept
technology	O
is	O
Ethernet	O
.	O
</s>
<s>
RapidIO	B-General_Concept
is	O
optimized	O
for	O
energy	O
efficient	O
,	O
low	O
latency	O
,	O
processor-to-processor	O
communication	O
in	O
fault	O
tolerant	O
embedded	O
systems	O
that	O
span	O
geographic	O
areas	O
of	O
less	O
than	O
one	O
kilometre	O
.	O
</s>
<s>
Time	B-Protocol
Triggered	I-Protocol
Ethernet	I-Protocol
is	O
a	O
competing	O
technology	O
for	O
more	O
complex	O
backplane	O
(	O
VPX	B-Architecture
)	O
and	O
backbone	O
applications	O
for	O
space	O
(	O
launchers	O
and	O
human-rated	O
integrated	O
avionics	O
)	O
.	O
</s>
