Embedded Systems Conference
Breaking News
Comments
Newest First | Oldest First | Threaded View
Roger Shepherd
User Rank
Author
Re: Power Management
Roger Shepherd   7/21/2013 1:50:55 PM
The analysis of power consumption is tricky and should take into account voltage-frequency scaling.

I believe the assertion "With a Cortex-A15, at five times the area and five times the power consumption, you can get two or three times the performance of the Cortex-A7" is a statement about what happens when the A15 and A7 are run at the same frequency and voltage. If we look at running the two processors at the same performance point then the frequency of the A15 can be one-half to one-third of the A7; that means that the A15 power will be 2.5x to 1.7x the A7 power at the same voltage. But the A15 design is being run slow - so the voltage can be dropped. Taking the figures shown on the ST-Ericssson blog* for 28FDSOI as guidance, dropping from 1.0V to 0.7V drops frequency by 2x. If we drop the voltage then the power consumption drop by a further 0.7^2 = 50% - so for applications where the A15 is 2x the performance of an A7 at the same frequency, the power consumption is 25% higher than A7, for those where A15 is 3x the performance of A7 the power consumption is at at least 15% better than A15.

For sure I've ignored leakage but its likely leakage is only really an issue at high-performance points which cannot be reached by an A7 anyway. 

Finally, it is also the case that to first order, from a power perspective, you woul dbe better using two half-fequency processors to do a job than 1 full-frequency. It's just there  is a little problem with software.

* http://blog.stericsson.com/blog/2012/04/st-ericsson-general/fd-soi-a-process-booster-for-st-ericssons-next-generation-novathor-part-1/

Peter Clarke
User Rank
Author
Re: Power Management
Peter Clarke   7/20/2013 5:17:29 AM
NO RATINGS
Yes CPUs support DVFS

Yes ARM did discuss other strategies that are part of build out of big-little...but I am planning for that to be topic of separate article. 

Kinnar
User Rank
Author
Re: Lower, slower, more energy efficient
Kinnar   7/19/2013 2:44:46 PM
NO RATINGS
Yes, You are right, It is a major area of research about optimizing the number of cores as compared with the performance. Turning on and off the cores as an when required dynamically is the present day solution while using more cores. Lets see if a major power improvement comes in the mean time by ARM.

LarryM99
User Rank
Author
Power Management
LarryM99   7/19/2013 1:39:23 PM
NO RATINGS
Peter, your point on multiple small cores versus a single larger one has power management implications as well. It gives the potion of shutting down cores to save power, as opposed to (or maybe in addition to) clock rate management. Do the new CPUs support both of these power management strategies? Did ARM discuss any improvements that they might have coming in terms of power management?

Peter Clarke
User Rank
Author
Lower, slower, more energy efficient
Peter Clarke   7/19/2013 12:38:24 PM
NO RATINGS
Of course these arguments also apply to the A53 versus the A57.



Most Recent Comments
David Ashton
 
sw guy
 
bec0
 
sixscrews
 
betajet
 
Brian Fuller2
 
zeeglen
 
tb100
 
Stargzer
Radio
NEXT UPCOMING BROADCAST
Why Connect a Car?
May 11, 1pm EDT Monday
Overview: Battle-hardened veterans of the electronics industry have heard of the “connected car” so often that they assume it’s a done deal. But do we really know what it takes to get a car connected and what its future entails? Join EE Times editor Junko Yoshida as she moderates a panel of movers and shakers in the connected car business. Executives from Cisco, Siemens and NXP will share ideas, plans and hopes for connected cars and their future. After the first 30 minutes of the radio show, our listeners will have the opportunity to ask questions via live online chat.
Top Comments of the Week
Flash Poll
Like Us on Facebook

Datasheets.com Parts Search

185 million searchable parts
(please enter a part number or hit search to begin)
Special Video Section
LED lighting is an important feature in today’s and future ...
Active balancing of series connected battery stacks exists ...
After a four-year absence, Infineon returns to Mobile World ...
A laptop’s 65-watt adapter can be made 6 times smaller and ...
An industry network should have device and data security at ...
The LTC2975 is a four-channel PMBus Power System Manager ...
In this video, a new high speed CMOS output comparator ...
The LT8640 is a 42V, 5A synchronous step-down regulator ...
The LTC2000 high-speed DAC has low noise and excellent ...
How do you protect the load and ensure output continues to ...
General-purpose DACs have applications in instrumentation, ...
Linear Technology demonstrates its latest measurement ...
10:29
Demos from Maxim Integrated at Electronica 2014 show ...
Bosch CEO Stefan Finkbeiner shows off latest combo and ...
STMicroelectronics demoed this simple gesture control ...
Keysight shows you what signals lurk in real-time at 510MHz ...
TE Connectivity's clear-plastic, full-size model car shows ...
Why culture makes Linear Tech a winner.
Recently formed Architects of Modern Power consortium ...
Specially modified Corvette C7 Stingray responds to ex Indy ...