蘋果iPhone 5中的A6處理器究竟使用了什么核心？為了一探究竟，我們實際解剖了A6，并與之前的A5X, A5進行了比較。 過去一段時間以來，猜測iPhone 5所用的A6處理器究竟使用哪一款核心幾乎已達狂熱程度。大部份討論集中在CPU和GPU的變種上。甚至可以說，這些核心就是所有討論的重點所在。業(yè)界普遍認(rèn)為，A(x)處理器不過是將CPU和GPU (現(xiàn)在都是多核心了)簡單地整合，加上一些晶體管，就能順利運作。但事情絕不可能這么簡單。 時間拉回2010年1月，在iPad推出之前，我曾經(jīng)談到過史帝夫.喬布斯 (Steve Jobs) 在2008年收購 PA Semi 。當(dāng)時喬布斯說：“我們希望經(jīng)由IC設(shè)計進一步實現(xiàn)產(chǎn)品的區(qū)隔化?！蔽乙恢庇浀眠@句話，并將之作為我們分析 A4 和 A5 處理器的大原則。而現(xiàn)在，我們也將以相同的原則來檢視 A5X 和 A6 。 A5X A5X 處理器變種出現(xiàn)在今年三月問世的 iPad 3月之中。該處理器的尺寸相對較大?？焖俦容^ A5 和 A5X 的芯片照片時可發(fā)現(xiàn)尺寸增加的主因是因為新增的兩個GPU核心。不過要我說，導(dǎo)致尺寸變大還有其它因素。

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A5的 GPU 大約30mm2，占總芯片面積的24%。而在A5X中，該數(shù)字增加至62mm2，占總芯片面積40%。而在這兩款芯片中，兩個ARM核心的面積大約都是18 mm2。 那么，導(dǎo)致整個芯片尺寸增加只是因為GPU嗎？簡單來說，答案是否定的。 A5X芯片尺寸為165mm2，大約比A5大43mm2。GPU部份增加了約32mm2，另外還有11mm2左右的增加面積。這對A5X來說似乎剩下太多了，因為這幾乎占A4芯片面積的25%。因此，里面必然藏有更多的設(shè)計。 除了CPU/GPU以外，依照我的計算，A5X上還有15個數(shù)字模塊，而A5是12個。此外，A5X上還有2個數(shù)組是A5所沒有的。這些「數(shù)組」已經(jīng)在A5X的芯片照片上標(biāo)注出來，它們很可能是包含微碼的ROM。 在CPU和GPU核心之外，芯片內(nèi)還有哪些奧秘？ 一些較普遍的組件包括有內(nèi)存橋、特定接口電路、其它外圍等。不過，還有其它不同的IP模塊，很可能包含了Anobit (已被蘋果并購)閃存控制器。另外，芯片內(nèi)還有一些進行專門任務(wù)處理的模塊。 A5X的額外11mm2是屬于“下落不明”的區(qū)域，我們認(rèn)為其中可能包含可進一步讓蘋果與其它產(chǎn)品區(qū)隔化的電路。 現(xiàn)在，終于快要進展到A6了。 本文授權(quán)編譯自EE Times，版權(quán)所有，謝絕轉(zhuǎn)載 本文下一頁：UBM TechInsights的A6拆解分析

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{pagination} 由于拆解專家們才剛剛拿到 iPhone 5 ，因此我們在等待首張芯片照片前，先用A(x)處理器的相關(guān)資料進行分析。 在9月12日推出iPhone 5時，蘋果披露的A6信息非常少，只有一個關(guān)鍵信息：A6比A5小22%。因此該芯片尺寸應(yīng)該是96mm2。芯片面積的減少很可能是因為從45nm跨越到32nm制程之故。A5X的芯片面積為165mm2，到96mm2至少縮減了41%。

Source：UBM TechInsightsbwsesmc

沒錯，確實有著相同的編號，但我認(rèn)為這不過是轉(zhuǎn)移注意力的噱頭罷了。要從這個數(shù)字來判斷有多少GPU/CPU核心是不可能的。芯片上還有一些非常有趣的電路。顯然，蘋果對新芯片做了更多的設(shè)計，而不是僅僅增加核心或重新排列模塊。 UBM TechInsights的A6拆解分析 《EE Times》姊妹公司 UBM TechInsights 認(rèn)為，iPhone 5中使用的A6處理器仍可能由韓國三星電子(Samsung)制造，并可能采用ARM的“big-little”繪圖處理器核心方案。 從 UBM TechInsights 的早期分析看來， A6 上有著與A4和A5類似的三星標(biāo)記。 根據(jù)UBM TechInsights的拆解分析，A6芯片尺寸為95.04 mm2，遠(yuǎn)小于A5X的162.54 mm2和45nm版本、尺寸為122.21 mm2的A5處理器。

蘋果A6芯片標(biāo)記。
Source：UBM TechInsightsbwsesmc

蘋果A6芯片照片。
Source：UBM TechInsightsbwsesmc

本文授權(quán)編譯自EE Times，版權(quán)所有，謝絕轉(zhuǎn)載 本文下一頁：使用者體驗才是王道

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{pagination} 仔細(xì)觀察UBM TechInsights的A6圖片，可發(fā)現(xiàn)只有3個處理器繪圖核心很容易辨認(rèn)。 UBM TechInsights技術(shù)研究經(jīng)理Allan Yogasingam指出，蘋果可能已經(jīng)采用了ARM的“big-little”技術(shù)，運用高性能核心和功效型核心的配對組合，來共享處理器資源，以降低整體功耗。 “蘋果或許已經(jīng)使用了“big-little”方式，搭配一顆較靈活或是較小的第四顆核心，”Yogasingam說?！盁o論采用哪種方式，蘋果的定制芯片都將是非常獨特的處理器設(shè)計?！?

A6處理器的放大圖，顯示了ARM核心和其它部份的位置。
Source：UBM TechInsightsbwsesmc

使用者體驗才是王道 當(dāng)工程師們談?wù)摰蕉ㄖ圃O(shè)計和/或降低芯片面積時，往往會陷入成本考量的陷阱。這能否增加利潤或降低芯片成本？但A5X破除了這種迷思。一切都將以終端使用者體驗為依歸。蘋果永遠(yuǎn)將使用者體驗置于成本考量之前?！度A爾街日報》的Walter Mossberg在最近一篇有關(guān)Kindle Fire HD的報導(dǎo)中指出，“Fire HD沒有iPad的優(yōu)雅、流線外形或是易用性......Fire HD一直給人延遲的印象，連應(yīng)用程序激活也會延遲。而這種延遲得重新開機才能解決?！? 蘋果寧愿消耗額外的硅晶面積和做更多設(shè)計，并使用他們熟悉的操作系統(tǒng)，以確保整體使用感覺更加流暢。 編按：本文其中一位作者Paul Boldt是加拿大技術(shù)研究公司ned, maude, todd & rod Inc.,的首席分析師。他的文章首先出現(xiàn)在www.engineering.com，經(jīng)作者同意后刊登于《EE Times》網(wǎng)站。 編譯： Joy Teng

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{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.