Archive for October, 2011

This blog originally posted on the Low Power Engineering Community 10/6/11. http://chipdesignmag.com/lpd/absolute-power

The iPhone 4S was announced today and frankly I was a little disappointed. No new iPhone 5, no 4G support, no bigger display or smaller form factor. But now that the initial disappointment has worn off, let’s take a look at what we DID get—pretty much the rumored iPhone 5 in an iPhone 4 package. There’s a faster processor with the A5, higher-resolution eight-megapixel camera for reasonable stills and 1080p video, a “fat” 64 GB version, wireless mirroring to HDTV displays via Apple TV, a world phone (GSM and CDMA support), and a whole host of new software features including expanded voice control, many new iOS 5 features, and iCloud to support wireless synchronization and cloud storage.

While I don’t have one to play around with yet, my first interest from a power standpoint will be to evaluate the impact of the A5 processor. We saw a measurable improvement in energy efficiency in the iPad 2 vs. the original iPad, partly attributable to the A5. Roughly doubling overall performance compared to the A4, the A5 is a dual-core processor and adds significant additional power-saving features to do more with less.

Even more interesting, though, will be an evaluation of a less-talked-about new hardware feature: A revamped antenna setup for the iPhone 5 is said to significantly improve reception and data speeds. That should mean fewer dropped calls. We’ll see about that because it won’t be hard to verify this claim. And if data reception is improved by any noticeable amount, I’m certain we’ll be able to see it in our standard “Star Trek streaming test.” With the Retina display remaining constant, we should be able to get some good comparison points on the new hardware.

And here’s the big secret in Apple’s strategy with the iPhone 4S—I expect that Apple TV unit sales will go through the roof. Wireless streaming to today’s huge HDTV displays for $99 is only a little more than double the cost of Apple’s $39 HDMI adapter (Apple Digital AV Adapter), which doesn’t even include the cable! Sign me up.

So no new iPhone 5, but plenty of new features to fiddle around with until the “5” arrives. See you in line!

This blog originally posted on the Low Power Engineering Community 9/8/11. http://chipdesignmag.com/lpd/absolute-power

We’ve been examining power efficiency of iOS devices for a while now, and it’s hard not to notice the relative trajectories of mobile operating systems and more traditional PC operating systems. With the recent release of OS X Lion, Apple is moving in the direction of converging capabilities of these platforms, with the clear goal of a more unified environment coming down the line.

When I first played with the iPad and iPad2, I thought I had purchased my last laptop computer. The portability and battery life of these tablets were so compelling that surely the days of the laptop were over, and it was only a matter of time before tablets ruled the portable computing category. And sure enough, in the last couple of years, tablets have multiplied faster than rabbits. But interestingly, none have taken significant share away from the runaway success of the iPad.

Then in late 2010 came the refresh of the MacBook Air, transforming an over-priced, under-powered specialty gadget into a mainstream computing device that has breathed new life into the entire laptop category. Sure, it was still at least one generation behind in raw compute power, but as we all know by now, it’s the combination of compute power with all of the other system parameters that determines utility today, and the 2010 MBA hit the center of the target. And to top it all off, less than one year later, the July 2011 MacBook Air refresh brings latest technology to this form factor, completing the repositioning of the MBA from a “snob’s machine” to one that can satisfy 80% of the market. I got my 13” MBA a few weeks ago, and have been impressed not only with its speed (1.7GHz Core i7 with 3MB cache, 4GB memory, and 128GB flash disk), but also its power efficiency (about five to six hours of typical use.) On the “Star Trek” power efficiency test, the 13” MBA fared very well—It made it through the entire 2:06 movie at maximum brightness and consumed about 22.5 Wh of energy, nearly the same as my 2010 11” MBA at 21.35 Wh.

My biggest dilemma now is which device(s) to bring with me? My arsenal now includes the iPhone 4, iPad 2, 11” 2010 MacBook Air, and 13” 2011 MacBook Air. All are very compelling, but a few factors make the determination easy, at least for now. First, the iPhone 4 is in. It’s the one device that I ALWAYS carry with me. Small, light, and utilitarian, it’s the 21st century Swiss army knife. The dilemma is, which additional device makes the cut? I’ve already decided that Internet access is best achieved through my phone via the personal hotspot feature, so that’s a wash. The iPad 2 is a wonderful machine. It still tops the list for the most compelling portable movie-watching device. Compared with all of the other devices, the display is big, crisp and clear, with deep rich colors, and exhibits the fewest artifacts. It’s a winner, but unfortunately iOS apps still restrict serious usage for entering or editing the standard documents that we all need to access, namely those created in Microsoft Office. Sure, it’s possible to upload/convert to Google Docs and edit online, but access isn’t 100%, and the interface is still a kludge in iOS, at best. I’m convinced that storage and editing in the cloud is the way of the future, but unfortunately, we’re stuck here in the present for now.

Which leaves me with two great choices for larger-format portable computing, the 2010 11” Air, or the new 2011 13” Air. The 2011 13” Air is a fantastic machine—blazingly fast and extremely power efficient. The display is significantly bigger than the 11” version, but so is its form factor. I’ve decided that my ultimate road warrior combo is my iPhone 4 coupled with the 11” MacBook Air. Everything I need, and super portable!

From the software standpoint, being able to run standard apps is certainly a compelling feature. Note to Microsoft: Where is that iOS Office app? Or maybe the operating systems are converging even faster. I’ve tapped the screen of my Air many times in the last few months, expecting a document to open, or a Web link to be followed. Certainly there are prototypes of touchscreen laptops deep in the research facilities at Apple. Plus, the large track pad and additional interface features in Lion (MacOS 10.7) are starting to make this laptop feel a lot like a tablet!

With this many great choices out there today, I can tell that my ultimate combo probably won’t last long. A converged iMacOS or big jump in performance and apps might well nudge the iPad (3?) back into the lead. But one thing’s for sure: I haven’t purchased my last laptop!

This blog originally posted on the Low Power Engineering Community 8/11/11. http://chipdesignmag.com/lpd/absolute-power

With the current popularity of all things extreme, from extreme dieting, extreme couponing and extreme hoarding, all the way to extreme sports and even extreme programming, I thought, “Why not Extreme Power Efficiency?” After all, power efficiency has been improving at a blistering pace for the last few years. Where will the hotspots and power bottlenecks be looking into the future?

Well, let’s start by rounding up the usual suspects. Dynamic and static power are the buckets into which we partition the energy that is used for computing (flipping bits), vs. the energy used to maintain power to the circuitry (sometimes also called standby power). For dynamic power, much of the focus today is on the back-end of the implementation flow—making sure that capacitances are minimized, dealing with many voltage areas or “islands,” and allowing dynamic variation of voltages and clock frequencies to conserve power. These problems aren’t completely solved today, and continue to expand as power architecture complexity increases, but they are reasonably well understood, with lots of people working on improvements in tools and methodologies. “Extreme” dynamic power efficiency might instead be measured in units of “transitions per function” to gauge the transition-efficiency of any implementation, combined with “joules per transition” for the physical layout and technology efficiency, to arrive at energy consumption estimates. As with any process, you can’t improve what you can’t measure, so thinking about measurements and metrics isn’t a bad place to start.

For static power, we are now pretty good at power gating or “shutdown” to minimize leakage power in unused blocks, and new technology improvements have at least postponed the dreaded explosion in leakage at smaller geometries. However, these problems won’t go away, so as we move forward, “extreme” thinking dictates that power gating will continue to become finer-grained—and to a certain extent the current move toward “3D” transistors is a move in this direction—with much better on-off characteristics such as faster performance and lower leakage. So as the technology enables new transistor designs that approach the “perfect switch,” the tradeoff between finer-grained power-gating vs. more efficient technologies continues to shift.

Finally, while it seems there’s an endless list of things that we need to (and can) worry about, remember that part of what we do everyday is to make practical decisions about priorities. Power efficiency is no different. Worrying about power consumption for one transistor may not seem like much, but multiply it by 3 billion transistors on a chip and suddenly you’re talking real power. At a macro level, an average no-load power (that means no phone on the other end) of 0.1W (0.5W just 3 years ago!) for a cell phone charger isn’t much, but multiplied by the 5 billion mobile phones in the world and 24/7, and you can see we’ve got a big problem. Extreme thinking doesn’t always point us to practical problems that need addressing immediately, but it does allow us to step “outside the box” for a bit just to see what might be out there.

This blog originally posted on the Low Power Engineering Community 7/21/11. http://chipdesignmag.com/lpd/absolute-power

I have an opportunity this month to do some tests using my iPhone (AT&T iPhone 4, 32G, iOS 4.3.3, Personal Hotspot) as a true business productivity tool. I’m travelling to Austin, and am hosting a two-hour WebEx video conference call through our WebEx/MeetingPlace infrastructure. I’ve decided to use my iPhone 4 as the wifi connection from my laptop for the WebEx session, as well as for the audio portion of the conference call in MeetingPlace. Supporting hardware is my HP EliteBook 2540p laptop, which is connected via VPN to our company infrastructure through my iPhone 4 personal hotspot.

The first thing to note (if you haven’t seen the TV commercials) is that this setup isn’t even possible on the Verizon iPhone 4 because it requires voice and data transmission simultaneously. So if it works, chalk one up for AT&T.

Setting up the hotspot is very easy. This is a regular tool in my arsenal now, usually used for connecting iPads and iPod Touches to the Internet. Interestingly, I’ve also found around the house that my other family members, who are on more data-limited plans, also like to use my personal hotspot to save their data allocation. The personal hotspot feature from AT&T doubles your data allocation to 4GB per month, so I’ve never had a problem with the data limit on this plan.

With my laptop connected to the Internet via WiFi, the VPN connection into the company is a no problem, and I’m ready to try things out. Starting up the WebEx session goes surprisingly smoothly; I’m worried that latency might be an issue, but no problems. Now the next trick: start up the conference call, as well. Our latest software update in WebEx allows the system to call each participant, including the host, so I enter my phone number, and voila! My phone rings, and I start the conference call. During the next 15 minutes, about 15 to 20 participants join the call and the WebEx, and we’re off.

In order to get as much data as possible during the call, I am recording the time, battery percentage, and signal strength, and have decided to run the first half of the meeting with my iPhone display ON, and the second half with the display OFF (except for occasional interrupts for me to record the data).

Running a full WebEx videoconference with a voice conference in parallel resulted in the following:

– Power consumption during first hour with display ON: 1.87W

– Power consumption during second hour with display OFF: 1.38W

Our first obvious conclusion is that the display seems to draw about 490mW of power at full brightness. This is interesting because in our previous tests (watching Star Trek), the difference in power between the display on full brightness vs. minimum brightness was about 300mW. So now we can approximate the missing piece of information about the iPhone 4 display. It seems to draw around 190mW from powered down to minimum brightness, and an additional 300mW for full brightness.

In addition, the data also continues to fill in our chart of power consumption as a function of signal strength. Previous tests showed the hotspot feature drawing about 920mW when used to stream Star Trek with two to three bars of signal. In this case we can approximate the power for streaming by taking the total power required with display off (1.38W), and subtracting the estimated power for the voice call (750mW, given Apple’s seven-hour talk time estimate), leaving about 630 mW for the personal hotspot with 4 bars of signal strength.

OK, I know this calculation is a stretch. I really have only one data point. The call power is purely a guess from the datasheet, and the volume of data for the WebEx conference vs. the Star Trek movie isn’t controlled (I forgot to reset the data monitor on my phone!). But it’s fun to see that 1) completely mobile video/audio conferencing is a reality, 2) it can all be done on a single smart phone, and 3) the order of magnitude of energy usage is very similar to streaming a movie. Point No. 3 reinforces our previous notion that power dissipation on today’s mobile devices is dominated by communications (radios and antennas), as opposed to computations (gigahertz or gigabytes). And that’s very interesting.

This blog originally posted on the Low Power Engineering Community 6/16/11. http://chipdesignmag.com/lpd/absolute-power

Last week was the annual pilgrimage of hardware designers to the Design Automation Conference, where the latest in tools and technologies are displayed for use in upcoming generations of computer and electronic devices. And it was no surprise that low-power design continues to expand across all facets of the design space, from LED lighting to smart phones and cloud computing.

For me, one of the memorable moments was the mention of a new acronym in Alan Gibbons’ tutorial “System-Level Design and Software Development for Energy Efficient Platforms: Challenges from Models to Methods” – RFTS stands for “Run Fast, Then Stop.” Could this be a viable new strategy in our unending quest for energy-efficient hardware design? Haven’t we shown that voltage reduction is the real winner, resulting in a squared reduction in power, and even more as frequency is reduced? Won’t the inevitable leakage current in idle mode swamp any potential gains, anyway?

The answers, as expected for any complex question, are “maybe,” “kinda,” and “sorta.” While by now we’re all used to clock gating to reduce dynamic power and multi-threshold transistors to control leakage, and even voltage reduction, power shutdown, and dynamic voltage/frequency scaling, the demand for more techniques to minimize energy consumption continues to grow. Once we’ve lowered voltages to the point where noise (and timing) margins are a concern, and we’re shutting down everything possible, what’s next? RFTS is one answer to the question of whether it’s more efficient to work slowly and constantly, or finish the job as fast as possible and take a break. Clearly the general answer depends on the effectiveness of any shutdown strategy, the level of speed control, and some knowledge of the input stream of work to be done.

I was struck by the similarity of these questions to the questions we’ve raised regarding iPhone power efficiency. When we tested the AT&T iPhone vs. the Verizon iPhone for video streaming a few months ago, the results seemed to come down in favor of coverage (and a stronger signal), but in areas of similarly weak and variable signal, having a faster network was a clear advantage. Receive fast, then stop – interesting!

Optimizing for energy efficiency continues to get more complicated, requiring better and higher level analysis to make the right decisions, and extending the challenges to the design community. That’s a good reason to return to DAC next year.

This blog originally posted on the Low Power Engineering Community 5/12/11. http://chipdesignmag.com/lpd/absolute-power

It’s been an exciting week for designers of low-power electronics, as well as consumers of mobile devices. Intel announced on May 4 that its Tri-Gate 3D transistor technology is ready for production on its 22nm process. The “Ivy Bridge” processors are being demo’ed now and scheduled for full production this year. Products containing Ivy Bridge processors will ship in 2012.

Analysts have been salivating at this new technology announcement, with much written about how this technology unlocks Moore’s Law for the future and bolsters Intel’s competitive position vs. ARM for low-power processors. But there’s been some inconsistency and confusion in the press about the technical claims for this technology, so I thought it would be fun to take a closer look.

Intel’s press release states: “The 22nm 3-D Tri-Gate transistors provide up to 37% performance increase at low voltage versus Intel’s 32nm planar transistors. This incredible gain means that they are ideal for use in small handheld devices, which operate using less energy to “switch” back and forth. Alternatively, the new transistors consume less than half the power when at the same performance as 2-D planar transistors on 32nm chips.”

Sentence No. 1: A 37% performance increase for low voltage applications (mobile devices) sounds pretty impressive, but that’s pretty much in line with what I’d expect in moving the technology node from 32nm to 22nm.

Sentence No. 2: This one’s just in there for marketing purposes, although the grammar implies that the “handheld devices” are switching “back and forth.” That’s more than a little confusing, even for an engineer—or maybe especially for an engineer.

Sentence No. 3: The key word here is “Alternatively”. This implies that you get 37% better performance in low-voltage (low-power) mode, OR 50% less power for the same performance in high-performance (high-power) mode. “Same performance“ here isn’t well-defined, but I’m assuming that means equivalent transistor performance (delay), not operating voltage.

Several press accounts have reported 37% better performance AND 50% less power, which isn’t consistent with the press release.

So what’s the bottom line, and how big of a deal is this? First of all, we’re going into production at the 22nm node. Second, the so-called 3D technology is indeed a breakthrough because it enables volume production at 22nm without the anticipated and feared exponential rise in leakage current. Intel uses the analogy of a skyscraper in its press release. It looks to me to be more of a rooftop deck–but decks are still a big improvement. And yes, I am excited!