apple processors: designed differently but here to stay

7/29/2019 Apple Processors: Designed Differently but Here to Stay

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Apple processors: Designed differently but here to

stay

Don Scansen, Paul Boldt

2/20/2013 1:33 AM EST

What's next in Apple's iPhone- and iPad- powering A-series processor family? Two expertsprognosticate.Rumors of an iPhone 5s and iPad 5 are already circulating. Nothing too intense yet but they are

there. When these two devices do land they will likely sport an A7 and A7X, respectively. That is,unless Apple pulls the plug on its custom chip design and opts for an off-the-shelf Intel product.This is not our hypothesis but it is out there, even on Wall Street.

At the end of November Doug Freedman, an RBC Capital Market analyst, floated the hypothesisthat Intel would fab Apple processors if Apple moved the iPad to an Intel processor. It almostsuggests the Apple-designed application processors (APs) are somehow a stopgap until somethinbetter appears. This seems like the perfect backdrop to look at the A-series family, think aboutthe evolution therein, and weigh the evidence for Apples semiconductor design intentions.

Before we get too far ahead of ourselves lets consider the A6 and A6X. The debut of the A6 alon

with the iPhone 5 was pretty much expected from both the hyperactive Apple rumor mill and thesimple logic of refreshing the AP in sync with the iPhone.

However, the appearance of the A6X, some 41 days later inside the iPad 4 was very muchunexpected. It was a little more than half way into the usual annual iPad refresh cycle and therewas only a vague, late warning from the Apple pundits.

Die photographs of the A6 and A6X that were first published by Chipworks, with our addedannotations, are reproduced below. Probably the single most striking feature of both is the in-house designed CPU. Going further, it was a custom design where the layout was performedmanually, instead of using the common automated place and route approach. In theirdiscussion

of the A6 ChipWorks commented: "This is a more expensive and time-consuming method of layouHowever it usually results in a faster maximum clock rate, and sometimes results in higherdensity." They go on to say: "In fact, with the exception of Intel CPUs, it's one of the first customlaid out digital cores weve seen in years!"

There isn't much to add except to say that Apple is serious about and making considerableinvestment in their design capabilities. So, regardless of the reason for the custom design, thisclearly supports the hypothesis that Apple is not producing placeholders while it waits for an Intelprocessor.
http://news.cnet.com/8301-13579_3-57556523-37/intel-inside-the-ipad-maybe-if-it-builds-iphone-chips-rbc-says/http://www.chipworks.com/blog/recentteardowns/2012/09/21/apple-iphone-5-the-a6-application-processor/http://www.chipworks.com/blog/recentteardowns/2012/09/21/apple-iphone-5-the-a6-application-processor/http://www.chipworks.com/blog/recentteardowns/2012/09/21/apple-iphone-5-the-a6-application-processor/http://www.chipworks.com/blog/recentteardowns/2012/09/21/apple-iphone-5-the-a6-application-processor/http://news.cnet.com/8301-13579_3-57556523-37/intel-inside-the-ipad-maybe-if-it-builds-iphone-chips-rbc-says/


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Apple's A-series family treeChipworks presented some quantitative numbers comparing the A6 and A6X, in their November1st discussion of the A6X. With a die size of 124 mm, the A6X is 28% larger than the 96.7 mm

A6.

The CPU consumes 15 mm on both parts, while the triple core GPU of the A6 weighs in at 16mm, and the quad core GPU on the A6X comes in at 35 mm.

From the above numbers it is apparent that beyond the additional 19 mm for the GPU the A6Xsports approximately 10 mm additional area. This may not seem like that much, but it is actuallyan area larger than the individual GPU cores.

In terms of accounting for this additional area we can again turn to Chipworks who noted that theA6X doubled the SDRAM interface width and included some new interface blocks. They alsoobserved one fewer PLL for the A6X which freed up some mm.

So we gain some area here and use a bit less there. The question though is whether there areother differences. We will take a look at this, but in the context of the evolving A-series family. Avisual interpretation of Apples chip lineage should help.

The Family Tree

An A-series family tree is presented below. Starting with the A4 in 2010 and ending with the A6Xjust a few months ago, there are now 5 members in the family. Basic information for each AP,including the device in which it was introduced, its dimensions (mm) and die size (mm2) areincluded. The tree has been constructed to schematically illustrate two major evolutions that haveoccurred within the family over the last three years. First, the original family line bifurcated into twdistinct lines of APs. Second, the family went through a process shrink from the original 45 nm tthe current 32 nm fabrication process. Each of these events will be considered in more detail.

The bifurcation

The X branch was introduced at the 5 generation with the A5X in March 2012. Its die size grewby 35% compared to the A5, i.e. the same generation of the other branch. At least some of thisextra area was due to a doubling of GPU real estate.

The increase in graphics horsepower compared to its generational counterpart emerged with afour-fold increase in the number of pixels from the iPad2 to the iPad3.

Further evidence of the bifurcation of the A-series family came in the digital blocks outside of theCPU, GPU and GPU spine. There are 12 for the A5 and 15 for the A5X.

What does this bifurcation look like at the 6 generation of the A-series family?

As pointed out above there is again much more real estate devoted to the GPU in the A6Xcompared to the A6. We also know about differences in the layout, interfaces and PLLs. It is timeto look at the digital blocks outside of the CPU and GPU.

There is most likely considerable block commonality between the two processors. Again referring
http://www.chipworks.com/blog/recentteardowns/2012/11/01/inside-the-apple-ipad-4-a6x-a-very-new-beast/http://www.chipworks.com/blog/recentteardowns/2012/11/01/inside-the-apple-ipad-4-a6x-a-very-new-beast/


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to Chipworks A6X article, Other than the CPU, it appears all the other digital cores have newlayouts, and many of the analog and interface cores have been reused from the A6, howeverthere are some new interface blocks.

But are there digital blocks on one die and not the other? We saw no comment on this. They didmention that the A6X sported considerable new design and was not just a tweak. It would,however, be interesting to consider whether there is evidence of a design overhaul in the form ofdifferent digital blocks, not just layout differences.

Looking at the die photographs, the A6 and A6X appear to have 17 and 16 digital blocks outside othe CPU, GPU and GPU spine, respectively.

For sure, there are blocks that are the same on both parts. The first thing to notice is that theshapes of the blocks differ between A6 and A6X. Obviously, floorplanning of the entire device isdependent on the number and location of the largest blocks (an additional GPU core in the A6X)leaving smaller blocks to be shoehorned into the available space. With no intention of minimizingthe task of re-shaping circuitry to fit major architectural changes, this floorplanning required morethan a copy and paste function.

There do however appear to be other differences, again beyond the PUs. We noted above thereappears to be a difference in the number of digital blocks.

Is there more?

Given a desire and the concomitant budget, hard-core reverse engineering is possible. Beyondreverse engineering the question of differences can be considered in two ways. One canqualitatively analyze the blocks to consider the amount of cache, for example. With this approachthe block labeled B in the A6 die photograph does not appear on the A6X, even consideringlayout differences.

One can also look at this more quantitatively, yet without a large reverse engineering project. Ofthe five digital blocks (see die photographs) most easily identified between the A6 and A6X, fouroccupy areas between eight and 10 percent larger or smaller than on the A6. The differences areat the upper end of measurement errors (we are relying on CW published die dimensions and theaccuracy of the associated image files posted on web sites), so are believed to represent minordesign changes within the blocks. The fifth digital block analyzed varied significantly between thetwo designs. The A6X version of this digital block was just over three times that of the A6.

Getting back to processor cores for a moment, there are four GPUs on the A6X compared to threeon the A6 (as noted by Chipworks). The design within each of these also differs significantly.

The GPU blocks on the A6 are 58% bigger than their A6 counterparts. Accounting for the GPU

cores along with the block that could either be a dedicated decoder or perform a GPU loadbalancing operation, there is nearly twice the die area directly devoted to graphics processing onthe A6X.The shrink

The second major evolution to date was the change from a 45 nm process to the current 32 nmprocess. The A5 was the first public part to be manufactured in the two processes, with the 32 nm

A5 appearing in the late winter / early spring 2012. Because of this shrink in fabrication processgeometry the raw die and block sizes do not provide a good comparison of the family members.To this end we have normalized die and block sizes to the 32 nm process. The results are shownin the table below.


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A number of things jump out from the table. First is the continued increase in 32 nm equivalentdie size for both processor streams as seen in the third column.

The A6 was introduced during the September 2012 keynote as being 22% smaller than itspredecessor. This is true on a silicon basis, but on a circuit basis i.e. corrected for the shrink, it is

in fact 36% larger. The same is true for the A6X which is 29 % larger than its 5 level sibling.

There are quite a few more transistors on these parts. Looking within the die, the corrected CPUarea is 50% larger with the custom designed cores on the 6 level parts. The area devoted to theGPU, on the other hand, has continually increased in the two streams.

While the iPad 4 maintained the same 3.1 million pixel count as the iPad 3, there was room toimprove the graphics capabilities of the A6X compared to the A5X. Thus, the 39% increase inGPU area on the A6X compared to the A5X was not to handle more pixels, but to provide muchbetter performance.

How are Apple design efforts progressing?

When we first wrote about theA4 for EETimes in 2010 we found that there were many similaritieswith the Samsung design. Later in 2011 when the A5 came along, we thought it was a bold stepforward, and speculated on possible avenues of customization for Apple because they control boththe integrated circuit design and the OS.

Probably the most striking thing about the A6/A6X is the Apple designed dual ARM core that eachsport. A close second would be the continued increase in circuits compared to earlier generationof the A-series family. So in summary, the A-series family has evolved into a serious bit of circuitdesign and is here to stay. Period.

Some parting thoughtsFirst, it will be interesting to see if the die size plateaus at some point.

With the pixel count now stabilized for the last two generations of 10.1 iPad, the added circuithorsepower is driving improved performance not more pixels.

Second, it will be interesting to see how the block count evolves going forward, with IP of the anoborauthentec acquisitions possibly showing up in future designs.

Finally, the big one: Will there be an Apple designed GPU? It is clear that the GPU is continuallyconsuming more silicon whether you look across the whole family our just within one branch.

Based on the move to a custom CPU design this may well be in the back of their head. Thequestion of sufficient engineering resources and/or graphics IP is a topic best left for another day.

About the authors:

--Paul Boldt is a principal analyst at Ned, Maude, Todd & Rod Inc., an Ottawa-based technologyresearch company.

--Don Scansen is a partner at IP Research Group, a technology consulting firm delivering serviceto intellectual property clients.
http://www.anandtech.com/show/6426/ipad-4-gpu-performance-analyzed-powervr-sgx-554mp4-under-the-hoodhttp://www.anandtech.com/show/6426/ipad-4-gpu-performance-analyzed-powervr-sgx-554mp4-under-the-hoodhttp://eetimes.com/electronics-news/4200451/Apple-s-A4-dissected-discussed--and-tantalizinghttp://www.eetimes.com/electronics-news/4215094/A5--All-Apple--part-mysteryhttp://www.gettingtechnologyright.com/deja-vu-apples-anobit-acquisition/http://www.engineering.com/ElectronicsDesign/ElectronicsDesignArticles/ArticleID/4689/AuthenTec-another-Apple-acquisition.aspxhttp://www.anandtech.com/show/6426/ipad-4-gpu-performance-analyzed-powervr-sgx-554mp4-under-the-hoodhttp://www.anandtech.com/show/6426/ipad-4-gpu-performance-analyzed-powervr-sgx-554mp4-under-the-hoodhttp://eetimes.com/electronics-news/4200451/Apple-s-A4-dissected-discussed--and-tantalizinghttp://www.eetimes.com/electronics-news/4215094/A5--All-Apple--part-mysteryhttp://www.gettingtechnologyright.com/deja-vu-apples-anobit-acquisition/http://www.engineering.com/ElectronicsDesign/ElectronicsDesignArticles/ArticleID/4689/AuthenTec-another-Apple-acquisition.aspx


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apple processors: designed differently but here to stay

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