17-05-2014, 03:00 PM
Is It Time for Clockless Chips?
[attachment=63387]
Vendors are revisiting an old
concept—the clockless chip—
as they look for new proces-
sor approaches to work with
the growing number of cellu-
lar phones, PDAs, and other high-
performance, battery-powered devices.
Clockless processors, also called
asynchronous or self-timed, don’t use
the oscillating crystal that serves as the
regularly “ticking” clock that paces the
work done by traditional synchronous
processors. Rather than waiting for
a clock tick, clockless-chip elements
hand off the results of their work as
soon as they are finished.
Recent breakthroughs have boosted
clockless chips’ performance, remov-
ing an important obstacle to their
wider use.
In addition to their efficient power
use, a major advantage of clockless
chips is the low electromagnetic inter-
ference (EMI) they generate. Both of
these factors have increased the chips’
reliability and robustness and have
made them popular research subjects
for applications such as pagers, smart
cards, mobile devices, and cell phones.
Clockless chips have long been a
subject of research at facilities such as
the California Institute of Technology’s
Asynchronous VLSI Group (www.
async.caltech.edu/) and the University
of Manchester’s Amulet project (www.
cs.man.ac.uk/apt/projects/processors/
amulet/).
PROBLEMS WITH CLOCKS
Clocked processors have dominated
the computer industry since the 1960s
because chip developers saw them as
more reliable, capable of higher per-
formance, and easier to design, test,
and run than their clockless counter-
parts. The clock establishes a timing
constraint within which all chip ele-
ments must work, and constraints can
make design easier by reducing the
number of potential decisions.
The downside
Clocks lead to several types of inef-
ficiencies, including those shown in
Figure 1, particularly as chips get larger
and faster.
Each tick must be long enough for
signals to traverse even a chip’s longest
wires in one cycle. However, the tasks
performed on parts of a chip that are
close together finish well before a cycle
but can’t move on until the next tick.
As chips get bigger and more com-
plex, it becomes more difficult for ticks
to reach all elements, particularly as
clocks get faster.
Lack of tools and expertise
Because most chips use synchronous
technology, there is a shortage of
expertise, as well as coding and design
tools, for clockless processors.
According to Jorgensen, this forces
clockless designers to either invent
their own tools or adapt existing
clocked tools, a potentially expensive
and time-consuming process.
Although manufacturers can use typ-
ical silicon-based fabrication to build
asynchronous chips, the lack of design
tools makes producing clockless proces-
sors more expensive, explained Intel
Fellow Shekhar Borkar.
[attachment=63387]
Vendors are revisiting an old
concept—the clockless chip—
as they look for new proces-
sor approaches to work with
the growing number of cellu-
lar phones, PDAs, and other high-
performance, battery-powered devices.
Clockless processors, also called
asynchronous or self-timed, don’t use
the oscillating crystal that serves as the
regularly “ticking” clock that paces the
work done by traditional synchronous
processors. Rather than waiting for
a clock tick, clockless-chip elements
hand off the results of their work as
soon as they are finished.
Recent breakthroughs have boosted
clockless chips’ performance, remov-
ing an important obstacle to their
wider use.
In addition to their efficient power
use, a major advantage of clockless
chips is the low electromagnetic inter-
ference (EMI) they generate. Both of
these factors have increased the chips’
reliability and robustness and have
made them popular research subjects
for applications such as pagers, smart
cards, mobile devices, and cell phones.
Clockless chips have long been a
subject of research at facilities such as
the California Institute of Technology’s
Asynchronous VLSI Group (www.
async.caltech.edu/) and the University
of Manchester’s Amulet project (www.
cs.man.ac.uk/apt/projects/processors/
amulet/).
PROBLEMS WITH CLOCKS
Clocked processors have dominated
the computer industry since the 1960s
because chip developers saw them as
more reliable, capable of higher per-
formance, and easier to design, test,
and run than their clockless counter-
parts. The clock establishes a timing
constraint within which all chip ele-
ments must work, and constraints can
make design easier by reducing the
number of potential decisions.
The downside
Clocks lead to several types of inef-
ficiencies, including those shown in
Figure 1, particularly as chips get larger
and faster.
Each tick must be long enough for
signals to traverse even a chip’s longest
wires in one cycle. However, the tasks
performed on parts of a chip that are
close together finish well before a cycle
but can’t move on until the next tick.
As chips get bigger and more com-
plex, it becomes more difficult for ticks
to reach all elements, particularly as
clocks get faster.
Lack of tools and expertise
Because most chips use synchronous
technology, there is a shortage of
expertise, as well as coding and design
tools, for clockless processors.
According to Jorgensen, this forces
clockless designers to either invent
their own tools or adapt existing
clocked tools, a potentially expensive
and time-consuming process.
Although manufacturers can use typ-
ical silicon-based fabrication to build
asynchronous chips, the lack of design
tools makes producing clockless proces-
sors more expensive, explained Intel
Fellow Shekhar Borkar.