<s>
EKA2	B-Language
(	O
EPOC	B-Language
Kernel	B-Operating_System
Architecture	O
2	O
)	O
is	O
the	O
second-generation	O
Symbian	B-Operating_System
platform	I-Operating_System
real-time	B-Operating_System
operating	I-Operating_System
system	I-Operating_System
kernel	B-Operating_System
,	O
which	O
originated	O
in	O
the	O
earlier	O
operating	O
system	O
EPOC	B-Language
.	O
</s>
<s>
EKA2	B-Language
began	O
with	O
a	O
proprietary	B-Application
software	I-Application
license	I-Application
.	O
</s>
<s>
In	O
October	O
2009	O
,	O
it	O
was	O
released	O
as	O
free	B-License
and	I-License
open-source	I-License
software	I-License
under	O
an	O
Eclipse	B-License
Public	I-License
License	I-License
.	O
</s>
<s>
In	O
April	O
2011	O
,	O
it	O
was	O
reverted	O
to	O
a	O
proprietary	B-Application
license	I-Application
.	O
</s>
<s>
Like	O
its	O
predecessor	O
,	O
EKA1	B-Language
,	O
it	O
has	O
preemptive	B-Operating_System
multithreading	I-Operating_System
and	O
full	O
memory	O
protection	O
.	O
</s>
<s>
Pluggable	O
memory	B-General_Concept
models	I-General_Concept
,	O
allowing	O
better	O
support	O
for	O
later	O
generations	O
of	O
ARM	B-Architecture
instruction	I-Architecture
set	I-Architecture
architecture	O
.	O
</s>
<s>
The	O
user	B-Application
interface	I-Application
of	O
EKA2	B-Language
is	O
almost	O
fully	O
compatible	O
with	O
EKA1	B-Language
.	O
</s>
<s>
EKA1	B-Language
was	O
not	O
used	O
after	O
Symbian	B-Operating_System
OS	I-Operating_System
version	O
8.1	O
,	O
and	O
was	O
superseded	O
in	O
2005	O
.	O
</s>
<s>
The	O
main	O
advantage	O
of	O
EKA2	B-Language
was	O
its	O
ability	O
to	O
run	O
full	O
telephone	O
signalling	O
protocol	B-Protocol
stacks	I-Protocol
.	O
</s>
<s>
Previously	O
,	O
on	O
Symbian	B-Operating_System
phones	O
,	O
these	O
had	O
to	O
run	O
on	O
a	O
separate	O
central	B-General_Concept
processing	I-General_Concept
unit	I-General_Concept
(	O
CPU	O
)	O
.	O
</s>
<s>
Such	O
signalling	B-Protocol
stacks	I-Protocol
are	O
very	O
complex	O
and	O
rewriting	O
them	O
to	O
work	O
natively	O
on	O
Symbian	B-Operating_System
OS	I-Operating_System
is	O
typically	O
not	O
an	O
option	O
.	O
</s>
<s>
EKA2	B-Language
thus	O
allows	O
personality	O
layers	O
to	O
emulate	O
the	O
basic	O
primitives	O
of	O
other	O
operating	O
systems	O
,	O
thus	O
allowing	O
existing	O
signalling	B-Protocol
stacks	I-Protocol
to	O
run	O
largely	O
unchanged	O
.	O
</s>
<s>
Real-time	B-General_Concept
guarantees	O
are	O
a	O
prerequisite	O
of	O
signalling	B-Protocol
stacks	I-Protocol
,	O
and	O
also	O
help	O
with	O
multimedia	O
tasks	O
.	O
</s>
<s>
However	O
,	O
as	O
with	O
any	O
RTOS	B-Operating_System
,	O
a	O
full	O
analysis	O
of	O
all	O
threads	B-Operating_System
is	O
needed	O
before	O
any	O
real-time	B-General_Concept
guarantees	O
can	O
be	O
offered	O
to	O
anything	O
except	O
the	O
highest-priority	O
thread	B-Operating_System
;	O
because	O
higher	O
priority	O
threads	B-Operating_System
may	O
prevent	O
lower-priority	O
threads	B-Operating_System
from	O
running	O
.	O
</s>
<s>
Any	O
multimedia	O
task	O
is	O
likely	O
to	O
involve	O
graphics	O
,	O
storage	O
and/or	O
networking	O
activity	O
,	O
all	O
of	O
which	O
are	O
more	O
likely	O
to	O
disrupt	O
the	O
stream	O
than	O
the	O
kernel	B-Operating_System
is	O
.	O
</s>
<s>
Inside	O
the	O
kernel	B-Operating_System
,	O
EKA1	B-Language
only	O
allowed	O
one	O
thread	B-Operating_System
(	O
plus	O
a	O
null	O
idle	O
thread	B-Operating_System
)	O
.	O
</s>
<s>
EKA2	B-Language
allows	O
many	O
threads	B-Operating_System
.	O
</s>
<s>
This	O
makes	O
it	O
much	O
easier	O
to	O
write	O
device	B-Application
drivers	I-Application
that	O
involve	O
complex	O
finite-state	B-Architecture
machines	I-Architecture
,	O
such	O
as	O
those	O
for	O
SD	B-Device
card	I-Device
memory	O
sticks	O
or	O
USB	O
flash	O
drives	O
.	O
</s>
<s>
Interrupts	O
are	O
handled	O
with	O
an	O
interrupt	B-General_Concept
service	I-General_Concept
routine	I-General_Concept
,	O
which	O
may	O
request	O
an	O
immediate	O
deferred	B-Language
function	I-Language
call	I-Language
(	O
called	O
as	O
soon	O
as	O
the	O
interrupts	O
are	O
processed	O
)	O
,	O
or	O
a	O
deferred	B-Language
function	I-Language
call	I-Language
,	O
which	O
is	O
queued	O
to	O
run	O
on	O
a	O
kernel	B-Operating_System
thread	B-Operating_System
.	O
</s>
<s>
Either	O
may	O
in	O
turn	O
communicate	O
with	O
user-side	O
threads	B-Operating_System
.	O
</s>
<s>
Power	O
management	O
in	O
EKA2	B-Language
was	O
largely	O
unchanged	O
from	O
EKA1	B-Language
.	O
</s>
<s>
The	O
exact	O
scheme	O
varies	O
between	O
phones	O
,	O
but	O
generally	O
the	O
null	O
thread	B-Operating_System
puts	O
the	O
CPU	O
and	O
peripherals	O
to	O
sleep	O
,	O
after	O
having	O
requested	O
a	O
wake-up	O
whenever	O
the	O
next	O
timer	O
is	O
due	O
to	O
expire	O
.	O
</s>
<s>
EKA2	B-Language
runs	O
on	O
ARM	B-Architecture
architecture	I-Architecture
CPUs	O
and	O
the	O
WINS	O
emulator	O
.	O
</s>
<s>
On	O
the	O
emulator	O
,	O
EKA2	B-Language
provides	O
somewhat	O
better	O
emulation	O
than	O
EKA1	B-Language
,	O
more	O
so	O
for	O
the	O
APIs	B-General_Concept
which	O
Symbian	B-Operating_System
OS	I-Operating_System
uses	O
to	O
represent	O
processes	B-Operating_System
.	O
</s>
<s>
In	O
EKA1	B-Language
they	O
did	O
n't	O
work	O
at	O
all	O
on	O
the	O
emulator	O
,	O
which	O
runs	O
as	O
a	O
single	O
Windows	B-Operating_System
process	I-Operating_System
.	O
</s>
<s>
Much	O
of	O
the	O
credit	O
for	O
EKA2	B-Language
goes	O
to	O
a	O
single	O
Symbian	B-Operating_System
kernel	B-Operating_System
engineer	O
,	O
who	O
began	O
the	O
project	O
as	O
an	O
experiment	O
many	O
years	O
before	O
it	O
became	O
an	O
official	O
part	O
of	O
Symbian	B-Operating_System
OS	I-Operating_System
.	O
</s>
