The synchronous processor chips of computers use a clock to time the entire chip. But this clock is also the cause of speed and power consumption headaches. Here is how an asynchronous chip overcomes these problems by eliminating the clock altogether. A presentation by Akshit Arora and Ankit Goyal for Computer Science Architecture (UCS401) at Thapar University, Patiala

1. Asynchronous
Microprocessor
The Clockless Future
Computer Science Architecture
Presentation By :
AkshitArora (101303012)
Ankit Goyal (101303022)

2. “Designers are realizing that distributing a
clock across ever more complicated systems is
becoming more and more difficult, and that
sooner or later it won't work”
Alain Martin
Professor
Computer Science
Caltech
built the first clockless microprocessor in 1989

3. What are Asynchronous Processors ?
• An asynchronous circuit, or self-timed circuit, is a sequential
digital logic circuit which is not governed by a clock circuit or
global clock signal.
• Unlike a conventional processor, a clockless processor
(asynchronous CPU) has no central clock to coordinate the
progress of data through the pipeline.

4. It may actually be even easier to implement
high performance devices in asynchronous, as
opposed to clocked, because:
Components can run at different speeds on an asynchronousCPU. All major
components of a clocked CPU must remain synchronized with the central
clock.
A traditional CPU cannot “GO FASTER" than the expected worst-case
performance of the slowest stage/instruction/component. When an
asynchronousCPU completes an operation more quickly than anticipated,
the next stage can immediately begin processing the results, rather than
waiting for synchronization with a central clock.

5. Why Asynchronous Design
• Better Power Efficiency
• Only activating functional units consume power
• Inactivated parts remain in “stand-by” state
• No wasteful power dissipation by glitches
• Higher Performance
• No global clock
• proceed data at appropriate rate of environment
• Do not propagate local delay globally
• Smaller Chip Size
• Less high-frequency EMI components due to small amplitude and wide
current peaks

6. Disadvantages
• Fewer people are trained in this style compared to synchronous design.
• Performance (speed) of asynchronous circuits may be reduced in
architectures that require input-completeness (more complex data path).
• Incompatible with commercial EDA tools

7. Brief History of Asynchronous Processors
ILLIAC I and ILLIAC II (first asynchronous
designs, University of Illinois)1952
The PDP6 (Programmed Data Processor-6) DEC
in 1960 was an asynchronous computer model1960

8. Brief History of Asynchronous Processors
•It was all forgotten because of timing and hiding
advantages of Clocked processor until the arrival ofVLSI
in early 1970s
•The first Caltech Conference onVLSI in 1979 had a
complete session on self-timed logic, as asynchronous
logic was called at the time, within an important paper
by Stucki and Cox on ‘synchronization strategies’ was
presented.

9. Brief History of Asynchronous Processors
The first single-chip asynchronous microprocessor was
designed at Caltech1988
The first family of asynchronous clones of the ARM processor
(Amulet) from University of Manchester1993
An 8-bit microprocessor byTokyo Institute ofTechnology
namedTITAC1994
Amulet2e andTITAC 21997

10. Brief History of Asynchronous Processors
• Also, in 1997,The Caltech group designed the MiniMIPS—an asynchronous
version of the 32-bit MIPS R3000 microprocessor.
• With a performance close to four times that of a clocked version in the same
technology for the first prototype, the MiniMIPS is still the fastest complete
asynchronous processor ever fabricated.

11. Brief History of Asynchronous Processors
• In 2004, Epson manufactured the world's first
bendable microprocessor called ACT11, an 8-bit
asynchronous chip.
• using low-temperature polysilicon thin-film
transistors on a plastic substrate
• With energy consumption reduced by 70 per cent
compared to the synchronous microprocessors now
in everyday use.
• Epson is now researching potential applications for
its invention

12. Conclusion
• It is entirely practical to design a processor without a clock.
• Quality of such processors have improved with time. Some are
commercially available
• Clockless and selftimed processors opens up horizons for a radical departure
in the main stream architectures to new and exciting areas.
• Asynchronous design is competitive with the best synchronous design in
power efficiency and is close in performance to them.

13. References
• http://www.electronicsforu.com/EFYLinux/efyhome/cover/January2008/Asy
nchronous%20Microprocessor.pdf
• http://en.wikipedia.org/wiki/Asynchronous_circuit#Asynchronous_CPU
• http://www.ubergizmo.com/2005/02/epson-develops-the-worldacutes-first-
flexible-8-bit-asynchronous-microprocessor/

14. THANKYOU