使用者体验才是王道
当工程师们谈论到定制设计和/或降低芯片面积时，往往会陷入成本考量的陷阱。这能否增加利润或降低芯片成本？但A5X破除了这种迷思。一切都将以终端使用者体验为依归。苹果永远将使用者体验置于成本考量之前。《华尔街日报》的Walter Mossberg在最近一篇有关Kindle Fire HD的报导中指出，“Fire HD没有iPad的优雅、流线外形或是易用性......Fire HD一直给人延迟的印象，连应用程序激活也会延迟。而这种延迟得重新开机才能解决。”
苹果宁愿消耗额外的硅晶面积和做更多设计，并使用他们熟悉的操作系统，以确保整体使用感觉更加流畅。
编按：本文其中一位作者Paul Boldt是加拿大技术研究公司ned, maude, todd & rod Inc.,的首席分析师。他的文章首先出现在www.engineering.com，经作者同意后刊登于《EE Times》网站。
编译： Joy Teng
{pagination}
Apple A6 processor has landed, sort of
Paul Boldt
What has Apple packed inside the A6 processor at the heart of the iPhone 5? In advance of our actual dissection of the A6, here’s what you should expect.
Speculation around the design of the A6 processor at the core of the iPhone 5 has reached a fever pitch in the last few days. All that I have seen so far focuses on particular variants of the CPU and GPU. One might even say these cores are the whole discussion. It is widely believed that the A(x) processors are simply a CPU and GPU (now with multiple cores) tied together with a bit of transistor glue that makes everything work. If true, that's a shame.
Back in January 2010, before the iPad was introduced, I recounted a comment Steve Jobs made after Apple's 2008 acquisition of PA Semi acquisition in April 2008. Paraphrasing Jobs: "We want to further differentiate our products through IC design." I have always taken this to heart, making it the working premise of our analyses of the A4 and A5. We now extend this approach to the A5X and forthcoming A6.
A5X
The A5X variant emerged in March with the introduction of the iPad3. It was a relative huge die. One can quickly compare the A5 and A5X die photos and see the majority of the increase in die size is related to the addition of two GPU cores. I say majority because there is more to it than that.
The A5 GPUs consumed approximately 30 mm2, or 24 percent of the total die area. This number increases to 62 mm2 , or 40 percent of the total die area for the A5X. In both cases, the dual ARM cores consume approximately 18 mm2.
Does this account for all the increase in die size? The short answer is no.
Inside A6
With a die size of 165 mm2, the A5X is approximately 43 mm2 larger than the A5. The 32 mm2 increase in GPU real estate leaves a remaining area of 11 mm2. That doesn't sound like too much for the A5X, but it is 25 percent of the total A4 die area. So there is additional design here.
I count 15 digital blocks outside of the CPU/GPU combo in the A5X compared to 12 for the A5. Beyond that are what appear to be two arrays on the A5X that are absent in the A5. These “arrays” have been highlighted on a partial A5X die photo. They might be ROM containing microcode.
What's the stuff outside of the CPU and GPU cores? It is a mixed bag.
Mundane stuff like memory bridges, specific interface circuitry, other peripherals and associated overhead make the whole thing operate. Then there are the various IP blocks that may well include the anobit (now Apple) Flash controller. Blocks that likely perform dedicated processing tasks are also seen.
We discussed the possibility of hardware-based encoder blocks in a recent A5 article. The general theme of “extra” area was cited by Microprocessor Report, which commented that 33 mm2 can not be accounted for. This squares with our earlier estimate of 34 mm2.
The extra 11 mm2 in the A5X falls into this group. I think this “unaccounted” area could include circuitry that breathes life into the Jobs comment about "further differentiation."
Now, the A6
With consumers and tear down specialists just now getting their hands on the iPhone 5, we'll await the first die photos. In them meantime, we must sift through bits of available information about the A(x) processor lineage.
As pointed out in an here, Apple released little information about the A6 during a Sept. 12 event. It did provide one key piece of information: The A6 is 22 percent smaller than the A5. This works out to a die size of 96 mm2. The reduction in die area is associated with the very likely process shrink from 45 nm to 32 nm. An A5X die area of 165 mm2 and a 41 percent reduction in area works out to 96 mm2.
Yes it is the same number, but I think it's a red herring. It's unlikely any interpretation of GPU/CPU cores can be extracted from this number. Again, it's more than simply accounting for the CPU/GPU area. There is some really interesting circuitry outside this combo. Apple is doing more than just rearranging the furniture.
User experience
A recent article in Anandtech really changed the A6 discussion. The article provides evidence that Apple actually designed its own ARM cores for the A6. The A6 we provide a clearer picture of Apple's CPU work since the PA Semi acquisition.
User experience is paramount
When engineers talk about custom design and/or reduced die area, they often fall into the economics trap. This is not about increased margins or reduced silicon costs. The A5X killed that notion. It is all about the end-user experience. Apple will always favor user experience over cost. In his recent review of the Kindle Fire HD, the Wall Street Journal's Walter Mossberg commented: “The Fire HD isn't as polished, fluid or versatile as the iPad ... the Fire HD showed signs of latency—apps and content displayed delays in launching. This latency disappeared after a reboot.”
Apple will consume extra silicon and design it with intimate knowledge of the OS to make sure theirs is a fluid experience. Remember, Apple’s silicon is about further differentiation of the iOS device. Nothing more. Certainly nothing less.
A peek inside Apple's A6 processor
Dylan McGrath
SAN FRANCISCO—Apple Inc.'s A6—the processor powering its new iPhone 5—is likely fabricated by South Korea's Samsung Electronics Co. Ltd. and may employ ARM's "big-little" graphics processor core scheme, according to a preliminary teardown of the handset done by UBM TechInsights.
Samsung was widely considered the favorite to build the processor for Apple, just as the company has done for previous generations, the A4 and A5. But tensions in the courtroom and elsewhere between the two companies in recent times led to speculation that Taiwan Semiconductor Manufacturing Co. Ltd. (TSMC) might displace the incumbent this time around.
[Get a 10% discount on ARM TechCon 2012 conference passes by using promo code EDIT. Click here to learn about the show and register.]
But UBM TechInsights said early analysis of the die markings of the A6 reveal markings that are similar to the Samsung markings found in the A4 and A5 processors. (Click to view an analysis and photo slideshow of the teardown).
Apple A6 die marking (source: UBM TechInsights).
The teardown analysis by UBM TechInsights concluded that the A6 die shrink of 95.04 mm2 is much smaller than the 162.54 mm2 of the Apple A5X processor and the 45-nm version of the A5 processor, which was also a large 122.21 mm2.
Apple A6 die photo (click on image to enlarge).
A detailed look at the de-caped A6 by UBM TechInsights revealed that only three of the processors graphics cores are easily identifiable.
Allan Yogasingam, a technical research manager at UBM TechInsights, said Apple may have employed ARM's so called "big-little" technique, which involves pairing a high-performance processor core and a power-efficiency tuned processor core to share processing duties in a cache-coherent combination, yielding overall power savings.
"Apple may have used a 'big-little' approach and gone with either a flexible fourth core or a smaller one," Yogasingam said. "Either way, it’s a very unique processor design which was expected from Apple’s custom approach to it."
A diffusion image of the A6 processor shows the location of the ARM cores and other elements (click on image to enlarge).
Source: UBM TechInsights
UBM TechInsights is owned by UBM plc, the same company that publishes EE Times.
扫码分享到好友
Source：UBM TechInsights
