Apple S1 Analysis

One of the biggest issues with the smartwatch trend that I’ve seen is that as a result of most companies entering the market with smartphone backgrounds, we tend to see a lot of OEMs trying to shove smartphone parts into a smartwatch form factor. There have been a lot of different Android Wear watches, but for the most part everything seems to use Qualcomm’s Snapdragon 400 without the modem. Even though A7 is relatively low power for a smartphone, it’s probably closer to the edge of what is acceptable in terms of TDP for a smartwatch. Given that pretty much every Android Wear watch has around a 400 mAh battery at a 3.8 or 3.85 volt chemistry to attempt to reach 1-2 days of battery life and a relatively large PCB, the end result is that these smartwatches are really just too big for a significant segment of the market. In order to make a smartwatch that can scale down to sizes small enough to cover most of the market, it’s necessary to make an SoC specifically targeted at the smartwatch form factor.

Capped Apple S1 SoC (Image Courtesy iFixit)

The real question here is what Apple has done. As alluded to in the introduction, it turns out the answer is quite a bit. However, this SoC is basically a complete mystery. There’s really not much in the way of proper benchmarking tools or anything that can be run on the Watch to dig deeper here. Based on teardowns, this SoC is fabricated on Samsung’s 28nm LP process, although it’s not clear which flavor of LP is used. It’s pretty easy to eliminate the high power processes, so it’s really just a toss-up between HKMG and poly SiON gate structure. For those that are unfamiliar with what these terms mean, the main difference that results from this choice is a difference in power efficiency, as an HKMG process has less leakage power. Given how little cost is involved in this difference in process compared to a move to 20/14nm processes, it’s probably a safe bet that Apple is using an HKMG process here especially when we look at how the move from 28LP to 28HPm at TSMC dramatically affected battery life in the case of SoCs like Snapdragon 600 and 800.

Decapped & Labeled S1 SoC (Image Courtesy ABI Research)

We also know that binaries compiled for the watch target ARMv7k. Unfortunately, this is effectively an undocumented ISA. We know that Watch OS is built on iOS/Darwin, so this means that a memory management unit (MMU) is necessary in order to make it possible to have memory protection and key abstractions like virtual memory. This rules out MCU ISAs like ARMv7m even if it's possible to add an MMU to such an architecture, so it’s likely that we’re looking at some derivative of ARMv7-A, possibly with some unnecessary instructions stripped out to try and improve power consumption.

The GPU isn’t nearly as much of a mystery here. Given that the PowerVR drivers present in the Apple Watch, it’s fairly conclusive that the S1 uses some kind of PowerVR Series 5 GPU. However which Series 5 GPU is up to debate. There are reasons to believe it may be a PowerVR SGX543MP1, however I suspect that it is in fact PowerVR's GX5300, a specialized wearables GPU from the same family as the SGX543 and would use a very similar driver. Most likely, dedicated competitive intelligence firms (e.g. Chipworks) know the answer, though it's admittedly also the kind of information we expect they would hold on to in order to sell it to clients as part of their day-to-day business activities.

In any case, given that native applications won’t arrive until WatchOS 2 is released I don’t think we’ll be able to really do much in the way of extensive digging on what’s going on here as I suspect that graphics benchmarks will be rare even with the launch of WatchOS 2.

Meanwhile, after a lot of work and even more research, we're finally able to start shining a light on the CPU architecture in this first iteration of Apple's latest device. One of the first things we can start to look at is the memory hierarchy, which is information crucial to applications that require optimization to ensure that code has enough spatial and/or temporal locality to ensure that code is performant.

As one can see, there’s a pretty dramatic fall-off that happens between 28 and 64KB of “DRAM”, as we exit the local maximum of L1 data cache, so we can safely bet that the L1 data cache size is 32KB given current shipping products tend to fall somewhere between 32 and 64KB of L1 data cache. Given the dramatic fall-off that begins to happen around 224KB, we can also safely bet that we’re looking at a 256KB L2 combined cache which is fairly small compared to the 1-2MB shared cache that we might be used to from today’s large smartphone CPUs, but compared to something like an A5 or A7 it’s about right.

If Apple had just implemented the Cortex A7 as their CPU of choice, the obvious question at this point is whether they’ve really made anything “original” here. To try and dive deeper here, we can start looking past the memory hierarchy and looking closer at the machine itself. One of the first things that is obvious is that we’re looking at a CPU with a maximum frequency of 520 MHz, which is telling of the kind of maximum power that Apple is targeting here.

Apple S1 CPU Latency and Throughput
Instruction Throughput (Cycles/Result) Latency (Cycles/Result)
Loads (ldr reg,[reg]) 1 N/A
Stores (str reg,[reg]) 1 N/A
Move (mov reg, reg) 1/2 -
Integer Add (add reg, reg, imm8) 1/2 -
Integer Add (add reg,reg,reg) 1 1
Integer Multiply (mul reg,reg,reg) 1 3
Bitwise Shift (lsl reg,reg) 1 2
Float Add (vadd.f32 reg,reg,reg) 1 4
Double Add (vadd.f64 reg,reg,reg) 1 4
Float Multiply (vmul.f32 reg,reg,reg) 1 4
Double Multiply (vmul.f64 reg,reg,reg) 4 7
Double Divide (vdiv.f64 reg,reg,reg) 29 32

Obviously, talking about the cache hierarchy isn’t enough, so let’s get into the actual architecture. On the integer side of things, integer add latency is a single cycle, but integer multiplication latency is three cycles. However, due to pipelining integer multiplication throughput can produce a result every clock cycle. Similarly, bitshifts take two cycles to complete, but the throughput can be once per clock. Attempting to interleave multiplies and adds results in only achieving half the throughput. We can guess that this is because the integer add block and the integer multiply block are the same block, but that doesn’t really make sense because of just how different addition and multiplication are at the logic level.

Integers are just half of the equation when it comes to data types. We may have Booleans, characters, strings, and varying bit sizes of integers, but when we need to represent decimal values we have to use floating point to enable a whole host of applications. In the case of low power CPUs like this one, floating point will also often be far slower than integers because the rules involved in doing floating point math is complex. At any rate, a float (32-bit) can be added with a throughput of one result per cycle, and a latency of four cycles. The same is true of adding a double or multiplying a float. However, multiplying or dividing doubles is definitely not a good idea here because peak throughput of multiplying doubles is one result per four clock cycles, with a latency of 7 clock cycles. Dividing doubles has a peak throughput of a result every 29 clock cycles, with a latency of 32 clock cycles.

If you happen to have a webpage open with the latency and throughput timings for Cortex A7, you’d probably guess that this is a Cortex A7, and you’d probably be right as well. Attempting to do a load and a store together has a timing that indicates these are XOR operations which cannot be executed in a parallel manner. The same is true of multiplication and addition even though the two operations shouldn’t have any shared logic. Conveniently, the Cortex A7 has a two-wide pipeline that has similar limitations. Cortex A5 is purely single-issue, so despite some similarity it can't explain why addition with an immediate/constant value and a register can happen twice per clock.

Given the overwhelming amount of evidence at the timing level of all these instructions, it’s almost guaranteed that we’re looking at a single core Cortex A7 or a derivative of it at 520 MHz. Even if this is just a Cortex A7, targeting a far lower maximum clock speed means that logic design can prioritize power efficiency over performance. Standard cells can favor techniques and styles that would otherwise unacceptably compromise performance in a 2+ GHz chip could be easily used in a 520 MHz chip such as device stacking, sleepy stack layout, higher Vt selection with negative active body biasing, and other techniques that would allow for either lower voltage at the same frequency, or reduced capacitance in dynamic power and reduced static leakage. Given that Cortex A7 has generally been a winning design for perf/W metrics, I suspect that key points of differentiation will come from implementation rather than architecture for the near future. Although I was hoping to see Apple Watch on a more leading-edge process like 14LPP/16FF+, I suspect this will be deferred until Apple Watch 2 or 3.

Design WatchOS: Time and Notifications
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  • Murloc - Monday, July 20, 2015 - link

  • Murloc - Monday, July 20, 2015 - link

    the reviewer has no hair??
  • ianmills - Monday, July 20, 2015 - link

    HAHAHAHA exactly. The apple watch is reviewed by someone who is self-concious enough to shave their arm hair. This explains why the review is so positive. Some people find self-esteem in odd places...
  • supermoon - Monday, July 20, 2015 - link

    That's just what some people's wrists look like bruh, including mine. what are you grasping at??
  • dsumanik - Monday, July 20, 2015 - link

    This entire article (photos and content) has been 'photoshopped' by apple PR. Hair and skin smoothed, bokeh added....look at how the watch is posed in the shots, it is amateur photography heavily post a lame viral marketing attempt.












    12K FOR THE 'EDITION' ?????????????


  • navysandsquid - Monday, July 20, 2015 - link

    Hate on brother lol butt hurt much its ok enjoy your droid turbo lol
  • Ryan Smith - Monday, July 20, 2015 - link

    "This entire article (photos and content) has been 'photoshopped' by apple PR. Hair and skin smoothed, bokeh added....look at how the watch is posed in the shots, it is amateur photography heavily post a lame viral marketing attempt."

    While we do use Photoshop for editing (once you get past basic cropping, you probably want Photoshop), to be clear here these photos haven't received any significant processing. The only work we do on our photos is lens/sensor correction and auto toning.

    The fact of the matter is that Josh is an excellent photographer (the best one among us, in fact), which is how he's able to pull off these amazing shots. So the fact that you think it has been heavily edited is flattering in a sense; we didn't have to edit them, we were able to take those photos naturally in the first place.

    And no, no one from Apple PR has touched the photos. Or the article.
  • BittenRottenApple - Monday, July 20, 2015 - link

    Worship the holy apple.

    The apple way, selling over expensive crap to stupid consumers that like to
    get robbed.

    This has been a disastrous launch in every respect. The iwatch is such an
    ugly piece of crap, it is truly unbelievable how a company, formerly known for
    its remarkable design, dares to put out such a crap ton of shit. Some
    characteristics are glaringly obvious and inherent to it: over expensive,
    hardly innovative, limited functionality and usability (need of an iPhone to
    make it work), looks exactly like a toy watch and so on.

    There are of course way better smart watches out there, especially from the
    likes of Samsung, Sony, Motorola, Asus, LG, simply put, there is no need for
    another piece of over expensive junk.

    Regardless of what the casing and strap are, it's still maybe $8 worth of electronics at best, a painfully tiny screen, awful battery life, absolute dependence on an iPhone for proper function, and in reality adding extra time to decide if the message your phone just pinged your wrist with is worth pulling the phone out for to reply with.
    The smart watch is a dumb idea in its current form. The Apple icrapWatch (tm) with its "Wealthy - Rich - Look how obscenely rich I am" case material tiers (seriously, the upgrade from plastic to red leather band is $7k? Not even a gold band available to justify that $17k price?) is the ultimate expression of that.
    Maybe in 5 years or so a transparent OLED screen over a traditional watch with these sensors to pop-up notifications long enough to be noticed but not need to be charged every two hours is when it'll make sense, but for now it's a useless gimmick that nobody really needs.

    Let's face it, the Apple Watch is a total and utter failure. The one called Sport edition doesn’t even has a dust, shock and water resistant exterior and thus fails in nearly every "sports" related usage scenario, albeit still costing nearly as much as an iPad, or, you know, a real watch, which works for years to come.
    And the luxury one? Oh god, 17k+ for this utter crapicious experience. If you’re a millionaire, donate that 17k+ to the EFF, the communist party, an union or consider that such an amount of money could save lives in many third world countries or help to preserve nature. Besides that, it doesn’t even look that luxurious compared face to face to Rolex standards, more like some sort of ugly, chubby toy enclosed in a thin, and tiny gold case. The functionality provided, if one even dares to call it that way, are utter crap too, nothing new, nothing exciting here, nothing Samsung, LG, Pebbles haven't been offering for years on a far superior basis. For example the Pebbles watch which costs
    less than 79$ and has 8 days of battery life, shows many of the notifications and info someone might need, all the while being water and dust proof, with changeable wristbands. Seriously, fuck this overpriced, environmentally obscene, eco terroristic icrapWatch (TM).

    Yet another fine addition to the long list of "Terrible Products Apple Makes to Gouge Money out of People".

    The new icrapWatch (tm) is a testament to Apple's collapsing technical acumen. They eliminate all ports providing no cable based connectivity at all? This craven stupidity should send the last adherents running. But running to what? Windows isn't even a viable option anymore, since it now is the most widespread commercial NSA gathering tool available, closely followed by Android, iOS and OS X.

    It's a sad day for people who need real smartwatches. Jony Ive is a pompous, clueless hack who should be fired and shot on the spot (or torn apart by a horde of rabid dogs) for introducing crippling regressions like this one.

    Look at this POS: No USB port, which won’t require an adapter to do anything. So if you aren’t going to require an adapter anyway, why not make that nonexistent port a modern port one: Thunderbolt. Thunderbolt can carry USB, video, Ethernet, external storage... ALL AT ONCE. And it can be daisy-chained, which would be hugely important when the icrapWatch (tm) would have ONLY ONE PORT. So WTF is Apple doing in not making its nonexistant port into a thunderbolt port?

    And again, are you kidding me? No thunderbolt connector? Now every sorry user of this pos doesn’t have to find a thunderbolt to USB C, a USB C to USB to HDMI, a USB to USB 3.0 period, a USB C to USB connector for apple’s time machine and also does not manage to don't short circuit all that with the AC/DC to USB C connectors, seriously ? Not worth 200$ new pile of hairy connectors for the brand new icrapWatch (tm), and that is called a revolution nowadays? No ********** way, the Pebbles is way superior, period.

    By the way, they're perpetrating no connectors at all. Thunderbolt is a much-needed step to a modern I/O standard. No connector is an outdated, abused standard that was designed primarily for Rolex watches. It's not suitable for external storage, video, or anything else requiring bulk data transfer with minimal CPU overhead. A nonexistant connector at all is a regression, a major step BACKWARD.

    Starting at $349.00----Less than $8.00 worth of hardware = ~$341.00 premium to use icrapWatch OS instead of windows. (Honestly the most expensive component of this icrapWatch (tm) is probably the screen.)
    Anyone with real work to do will not even be able to buy this thing. My friend’s last Air was neat in that it was small and lasted all day, but it was so under-powered, it was frustrating. I can only imagine how limited this machine will be.

    Who cares about price, weight and size, when this product is crippled by a hopelessly defective design? You can't hook up a power adapter and external storage at the same time. You can't hook up an external display and external storage. Hell, you can't even plug in a thumb drive!

    This product is the most asinine piece of shit Apple has produced, and that includes the (thankfully) short-lived Shuffle that could only be controlled by a gimped Morse code.

    $270 less gets you the new Pebbles which will eat the crapWatch's lunch.

    If you need to do a lot of processor intensive work, than you would not even go near this thing. It would be useless to you. If you need to crunch spreadsheets or are heavy in corporate analysis, this icrapWatch (tm) would also be useless to you.

    This is the kind of icrapWatch (tm) that Apple sells a lot of. This icrapWatch (tm) is largely useless for anything other than email and facebook. It cannot store many files, it cannot process much information, and it has no external port. There is nothing wrong with using this icrapWatch (tm) for casual tasks, but it is CERTAINLY not a productivity machine.

    It is what it is. A status symbol/statement. Or some other statement. A statement that you just bought a $349 or icrapWatch(tm) with a $341 or more case so you can show off in front of your hipster isheep friends.

    I hate to stick to Apple only facts here, but Apple said that the current Samsung Smatwatch is 24% thicker than this new icrapWatch (tm). That does NOT mean that the new icrapWatch (tm) is 24% thinner than the current Samsung Smatwatch , it means that it is ~20% thinner than the current Samsung Smatwatch. They clearly phrased it that way to make it sound more impressive and hence dupe the consumer, aka stupid isheep.

    So, it's a toy watch plus with a display and no over expensive dongle so you can’t do everything a Pebbles can do, at more than four times the price while looking posh.
    And here I thought technology was about function over form. I get it, functional art; art I can do things my phone does, but in a space that anyone can see me doing it, stylishly. Crippled and non standard in-house branded "business" software does great, can't do anything really artistic on it except maybe GarageBand or stock filter photo edits to my innumerable selfies, but it's got that partially eaten fruit on the back that screams "money I'm too stupid to keep or invest wisely."

    Take my money!
    I wouldn't hold my breath.

    This is apple's marketing strategy: mind-numbing markup on dirt-cheap, mediocre icrapWare (tm). They throw together a cheap little toy like icrapWatch (tm), pretty it up with silver or gold paint, and ride the wave of ignorance, outrageous markup, and marketing that they've been using as a business model for many, many years now. The only thing Apple has ever made that's less worthless than all the other crap their conspirators like Hon Hai Precision Industry Co., Ltd excrete all day and night by taking advantage of child labour are iOS and OS X which, besides being notoriously crippled and constrained walled gardens, aren’t even worth the hassle unless you also dumped thousands of dollars into other apple products.

    Many apple owners I’ve encountered never stop trying to belittle and demean others because they don’t have a Macbook or an iPhone (or an icrapWatch (tm) for that matter) and then try to act like their overpriced apple products are overall better when they are certainly not, by any standard.

    Luxury cars, while still worthless crash grabs, usually offer some quality and features that are actually somewhat superior to cheaper competing vehicles and models.
    icrapWatch (tm) such as this start already expensive as hell with little performance to warrant such outrageous costs. Apple isn’t the luxury car of anything. It’s the luxury car DESIGN with a 4-cylinder under the hood and a tape-deck in the sound system, all with the price tag of "luxury". They sell laptops made cheap in china, using child labour and the same hardware you can find in SO many other laptops, slap their OS on it, put it in a thin case, and then markup the price by 300% to 600%. These are the facts. This icrapWatch (tm) in question is nowhere NEAR worth that kind of money. I mean, smartwatches in general are overpriced, but apple has made their entire business model out of extreme markups backed by clever marketing with little actual technological superiority of any kind. Every single apple product on the market can be outperformed in every way by comparable products. Apple icrapWatches (tm) can be outperformed by smartwatches that are FAR FAR cheaper while relying on older tech. The only thing that apple has that nobody else does is OSX and iOS, their operating systems. These are mediocre operating systems, but they are literally designed to be limited on anything it determines to be "non-apple hardware". Other operating systems can be installed on just about any computer you can slap together, whereas OSX is specifically and deliberately designed to be non-functional on ANYTHING that isn’t made by apple. It’s nothing but a cash-grab.

    Apple is indeed playing run-of-the-mill capitalism, they try to capitalize on the ignorance of the average consumer with marketing campaigns designed to make you assume you're getting your money's worth.

    There are millions of consumers who are on the fence, who are actually interested in buying something that's worth the money they spend. Those people deserve factual information and do not deserve to be exploited for their ignorance on the topic. So excuse me if I have a problem with it. College students especially, who don’t have a lot to spend in the first place, are being taken advantage of in every area of their life. Buying a smartwatch should be one less area of exploitation. This is why I have a problem with apple and with many other companies and services that attempt to capitalize on ignorance.

    Years down the road when the batteries in this model are dead and you have to keep it plugged in just to use then you'll have no way to plug in a flash drive or an external hard drive. I don't care how sexy it looks: sometimes and more often than not less means a serious lack of functionality.

    We can only hope that consumers send this piece of diabolic garbage to oblivion, as they did the idiotic iPod Shuffle that could only be controlled with Morse code over a proprietary headphone wire.

    The Apple Iphone 1 and Ipad 1 might have been innovative at their time,
    but since then, the bitten apple has been continuously rotting from the inside
    outwards, always swarmed by millions of Iworms which regale themselves with its
    rotten flesh, not forgetting all other Americans who support apple by means of
    their tax dollars to finance its bought US Treasury/Government bond interest rates.

    Last but not least, every Apple product includes a direct hotlink to the NSA,
    free of charge, something that might make it a good value, after all.

    Ceterum censeo Applem esse delendam.
  • twanto - Monday, July 20, 2015 - link

    "There is nothing wrong with using this icrapWatch (tm) for casual tasks, but it is CERTAINLY not a productivity machine." I was really hoping it could handle some spreadsheets and a bit of 3D rendering, but I guess not.

    This post was either satire or the greatest literary achievement by someone with a bonus chromosome 21.
  • Schickenipple - Tuesday, July 21, 2015 - link

    Word. If you are trying to create spreadsheets on your watch, or any screen that small, you are an idiot.

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