A11 Chip's 6-Core Architecture Highlights Apple's Continuing Push Into Heterogeneous Computing

In the recent leak of information from Apple, a device tree shared by Steven Troughton-Smith and containing information specific to the iPhone X was used to glean CPU code names, presence of an OLED display, and information on many other things. Contained within that information were also specific details regarding the architecture behind Apple's new CPU cores, dubbed "Mistral" and "Monsoon." From this, we know that the A11 contains four Mistral cores and two Monsoon cores, and it's worth taking a technical look at what Apple might be up to with this new chip.

a11 chip 1


While the two Monsoon cores are clear follow-ons to the two large "Hurricane" cores in the A10, the Mistral cores double the small core count of two "Zephyr" cores in the A10.

a10 small cores

September 2016 event slide on the two Zephyr cores in the A10

Annotated die shots ultimately revealed that the small Zephyr cores appeared to be embedded within the larger Hurricane cores, taking advantage of their geographic location by sharing memory structure with the Hurricane cores.

chipworks a10 die photo

Chipworks/TechInsights annotated A10 die photo showing small Zephyr cores embedded within large Hurricane cores (right)

The Mistral cores appear to be a departure from the above scheme, at the very least in that they have doubled in count. Specific references in the device tree are also made to memory hierarchy, suggesting that they contain independent L2 caches, meaning the Mistral cores could be more independent than their A10 ancestors.

This independence is underscored by the fact that the Mistral cores share a common "cluster-id" property, while the Monsoon cores share a distinct cluster-id of their own. Immediate comparisons were drawn to ARM's big.LITTLE heterogeneous CPU core scheme with the A10, and this seems to be going further down that path with distinct operating states for each cluster of cores. However, those leveraged shared resources in the A10 were to a certain benefit, namely die space and power consumption. The cores becoming more independent is more like a traditional big.LITTLE approach, which also entails more overhead.

This all may be an oversimplification, of course. After all, we know that each of these CPU cores is independently addressable, meaning that nothing revealed so far indicates an active Mistral or Monsoon core (or cluster) precludes the other CPU type from also being active, opening the door for mixed processor scenarios. Apple could have decided to spend effort, either in hardware, compilers, or both, to segregate instructions by complexity and ultimately forward them to the core that would execute them mostly efficiently.

Tackling problems in this manner would be another example in a long list of Apple's attempts to improve instruction execution efficiency through microarchitecture enhancements.

Any architectural changes ultimately circle back to improvements in some way. If Apple is making a change that includes doubling the amount of lower power cores, it seems inevitable it's ultimately spending more die space to do so, particularly if they have their own cache structures from L2 and down.

Yet, as pointed out by AnandTech editor Ian Cutress, ARM has begun allowing for configurable cache sizes for its offering of cores. In this specific case, a non-existent L2 cache is a valid configuration, meaning the increase in die space may not be as much as it initially seems with the small core count growth.

It's important to remember that Apple is not bound to these ARM conventions, but they are an indication of where the industry is headed. It's also important to remember that the shared L3 cache is always sitting above all of the cores, along with the GPU and image signal processor. Ultimately, these architectural changes likely boil down to a performance per watt increase, instructions per clock cycle increase, or perhaps both. Given that the small tasks a Mistral core might be activated for would likely not expose the parallelism needed for all four cores, it seem some interesting usage scenarios are a strong likelihood with Apple's A11 SoC.

To give the mixed-core ensemble of the A11 context, modern CPUs aggressively manage performance and power consumption by dynamically changing clock speeds, processor voltages, and even disabling entire CPU cores by gating clocks and powers to these cores. There are numerous references to all of these concepts in the software, in addition to several references of dynamic CPU and core control, as well as instructions per clock cycle, memory throughput thresholds, power thresholds, and even hysteresis to keep the cores from spinning up and down as the performance profile changes. No doubt many of these properties existed in the A10 as well, but the fact that Apple is increasing small core count shows Apple believes there's more benefit to be had here.

iphone x tree bcm4357

Reference to "bcm4357" in iPhone X device tree

There are more details contained than just the CPU and OLED display, however. The software specifically calls out Broadcom's BCM4357 as the Wi-Fi module. This is curious because the BCM4357 is actually a very old Wi-Fi chipset. It seems likely that Apple truncated the trailing 0 from the BCM43570, which fits the 802.11ac profile of the iPhone 7 (and thus, not an upgrade). However, Broadcom does have a BCM4375 chip on the horizon which supports the forthcoming 802.11ax standard. Unless the keynote specifically addresses the Wi-Fi speeds, we may not immediately get clarification here, given the Wi-Fi module is often embedded in a larger module, often by component integrator Murata.

Moving over to the display side, the peak brightness in nits property seems to be referenced to a full scale value, rather than an actual decimal nits value, unfortunately. This could have given insight into whether Apple sought to pursue any of the existing HDR standards on the market, which often require a peak brightness over 1000 nits.

In the audio realm, the CS35L26 reference confirms another Cirrus Logic win for the top and bottom speakers, and the CS42L75 is an undocumented audio codec. Finally, for pure trivia, there's a reference to a 'sochot' property that curiously references the A6X chip identifier. It also contains an 'N41' reference in the baseband section, which refers to an iPhone 5 codename that introduced LTE to the iPhone families. These may, however, simply be references to old devices when features or properties were first introduced.

Apple will undoubtedly reveal some details on the new A11 chip and other internal upgrades for the new iPhones at its event that's just a few hours away now, but other information will have to wait until teardown firms can get their hands on the devices and have a closer look at what's inside.

Top Rated Comments

macduke Avatar
53 months ago
A technical article on MacRumors?

MORE PLEASE.
Score: 36 Votes (Like | Disagree)
zakarhino Avatar
53 months ago
Great to see an article like this breaking down the A11 chip, nice change from all of the traditional speculation about the iPhone.

More of this in the future please!
Score: 24 Votes (Like | Disagree)
Padriac Avatar
53 months ago
Apple doesn't utilize the iphone's full capability. It's not the consumers fought. Other phones can do split screen, PIP, VR, convert to a PC, HDMI/mhl support, multitasking, real file manager, mouse/trackpad support, and stylus capabilities and still get stellar ratings and reviews. Apple forces it's fans to support face recognition and AR. Seriously besides the OLED screen and heavily criticized design. This is not that much of a upgrade. In terms of Touch ID, it may be a downgrade.

By not allowing them to do any of what's mentioned above, they will never utilize it's full capabilities since Apple limits the consumer.
You seem to confuse interface choices as having something to do with "power". Interface choices have nothing to do with power.

* Split screen: this is already done, but on the iPad because splitting a small screen is of limited value
* PIP: this is already done, but on the iPad since having PiP on a small screen is of limited value
* HDMI support: this is practically already obsolete in the age of Airplay and Chromecast. Might as well add a VGA port. And there's always a dongle if you need one
* Multitasking: are we really still arguing about this like we're back on iOS 9? What multitasking are you doing on Android that you're not accomplishing on iOS?
* Real File Manager + Mouse/trackpad support: iOS is an OS with 2 basic underlying philosophies: a touch (finger) interface and an application-centric rather than file-centric approach. If you take either of these away you just have Mac OS X. Apple already makes plenty of devices that use OS X.
* Stylus capabilities: we know exactly how Apple feels about stylus support by how the handle the Apple Pencil: an option for special cases, not something you need everyday on your phone.

Your idea of progress for a phone is to turn it into an old laptop. Why look backwards?
Score: 18 Votes (Like | Disagree)
Feenician Avatar
53 months ago
wow! with this A11 (Fusion) chip our Facebook, Twitter, Snapchat and other social media feeds will load faster then light! :p:p
Ha ha! People only use Apple devices for Facebook! Wheeeeeeeee!

:rolleyes:
Score: 12 Votes (Like | Disagree)
swankier Avatar
53 months ago
The BCM4375 provides 2x2 MIMO 802.11ax along with Bluetooth 5.0. *

So now we know why there are new AirPods.

Source: https://en.wikipedia.org/wiki/IEEE_802.11ax
Score: 10 Votes (Like | Disagree)
Eorlas Avatar
53 months ago
A technical article on MacRumors?

MORE PLEASE.
I agree. This is pretty awesome
Score: 8 Votes (Like | Disagree)

Top Stories

calculatorapp

iOS 11 Bug: Typing 1+2+3 Quickly in the Calculator App Won't Get You 6

Tuesday October 24, 2017 2:03 pm PDT by
A bug in the built-in Calculator app in iOS 11 is getting some major attention this week, despite the fact that it's been around since iOS 11 was in beta testing. At issue is a calculator animation that causes some symbols to be ignored when calculations are entered in rapid succession. You can try it for yourself: Type 1+2+3 and then the equals sign into the Calculator app quickly. Due to...
gradiente iphone white

Brazilian Electronics Company Revives Long-Running iPhone Trademark Dispute

Tuesday May 19, 2020 1:06 pm PDT by
Apple has been involved in a long-running iPhone trademark dispute in Brazil, which was revived today by IGB Electronica, a Brazilian consumer electronics company that originally registered the "iPhone" name in 2000. IGB Electronica fought a multi-year battle with Apple in an attempt to get exclusive rights to the "iPhone" trademark, but ultimately lost, and now the case has been brought to...
original iphone

Phil Schiller Says iPhone Was 'Earth-Shattering' Ten Years Ago and Remains 'Unmatched' Today

Monday January 9, 2017 7:15 am PST by
To commemorate the tenth anniversary of the iPhone, Apple marketing chief Phil Schiller sat down with tech journalist Steven Levy for a wide-ranging interview about the smartphone's past, present, and future. The report first reflects upon the iPhone's lack of support for third-party apps in its first year. The argument inside Apple was split between whether the iPhone should be a closed...
iphone 12 colors 2021

iPhone 12 Colors: Deciding on The Right Color

Thursday November 5, 2020 8:35 am PST by
The iPhone 12 and iPhone 12 Pro arrived last October in a range of color options, with entirely new hues available on both devices, as well as some popular classics. The 12 and 12 Pro have different color choices, so if you have your heart set on a particular shade, you might not be able to get your preferred model in that color. iPhone 12 mini and iPhone 12 The iPhone 12 mini and iPhone 12...
iPhone 13 Dummy Thumbnail 2

Full iPhone 13 Feature Breakdown: Everything Rumors Say We Can Expect

Tuesday August 31, 2021 7:50 am PDT by
With the launch of Apple's iPhone 13 lineup believed to be just a few weeks away, we have compiled all of the coherent rumors from our coverage over the past year to build a full picture of the features and upgrades coming to the company's new smartphones. For clarity, only explicit improvements, upgrades, and new features compared to the iPhone 12 lineup are listed. It is worth noting that...
omg lightning cable comparison

Security Researcher Develops Lightning Cable With Hidden Chip to Steal Passwords

Thursday September 2, 2021 6:59 am PDT by
A normal-looking Lightning cable that can used to steal data like passwords and send it to a hacker has been developed, Vice reports. The "OMG Cable" compared to Apple's Lightning to USB cable. The "OMG Cable" works exactly like a normal Lightning to USB cable and can log keystrokes from connected Mac keyboards, iPads, and iPhones, and then send this data to a bad actor who could be over a...
macbook air deals

Deals: Amazon Drops Price of 256GB M1 MacBook Air to New Low of $849.99 ($149 Off)

Friday August 27, 2021 6:16 am PDT by
Amazon today introduced new low prices on the M1 MacBook Air for both 256GB and 512GB storage options. To start, you can get the 256GB model for $849.99, down from an original price of $999.00. Note: MacRumors is an affiliate partner with Amazon. When you click a link and make a purchase, we may receive a small payment, which helps us keep the site running. Only Silver and Gold are...
maxresdefault

New MacBook Pro Models Coming at WWDC, Suggests Leaker

Monday May 24, 2021 1:27 pm PDT by
New MacBook Pro models are coming at WWDC, according to leaker Jon Prosser who has a mixed track record when it comes to predicting Apple's plans. Subscribe to the MacRumors YouTube channel for more videos. Prosser provided no additional information, but there are new 14 and 16-inch MacBook Pro models in the works. The new MacBook Pros will feature the most radical redesign to the MacBook Pro ...
M1X MBP Feature

Leaker: Upcoming MacBook Pro to See Price Hike Over Current Model, Equal Performance Across 14 and 16-Inch Sizes

Tuesday August 24, 2021 5:28 am PDT by
The upcoming 14-inch MacBook Pro is set to be more expensive than the current 13-inch MacBook Pro and both the 14 and 16-inch models will offer the same performance, according to the leaker known as "Dylandkt." The leaker shared the information on Twitter, explaining that both of the upcoming MacBook Pro models, expected to come in 14 and 16-inch sizes, will feature the same performance due...
iPhone 13 Dummy Thumbnail 2

Kuo: iPhone 13 to Feature LEO Satellite Communications to Make Calls and Texts Without Cellular Coverage

Sunday August 29, 2021 7:39 am PDT by
The iPhone 13 will feature low earth orbit (LEO) satellite communication connectivity to allow users to make calls and send messages in areas without 4G or 5G coverage, according to the reliable analyst Ming-Chi Kuo. In a note to investors, seen by MacRumors, Kuo explained that the iPhone 13 lineup will feature hardware that is able to connect to LEO satellites. If enabled with the relevant...