Inside the iPhone 6s | Hacker News Reader

Inside the iPhone 6s

chipworks.com

96 pointsshawndumas24 comments

Isn't 8mb of L3 cache a huge amount for a phone with 2 gigs of ram? A $260 Intel i5 6600 only has 6mb

Perhaps by comparison with desktop CPUs, but since the A8 had 4MB of L3, presumably there are good reasons for Apple to include more L3 in the A9. It may well be that Apple has found that a larger L3 cache contributes more to overall performance (or power efficiency) than, say, faster clocks or more RAM.

I suspect the L3 can also be accessed by the GPU since they share the memory management unit block. It probably contributes heavily into better GPU performance, seeing as the GPU in the SoC doesn't have its own dedicated high performance RAM, and the largest complaint I've seen from mobile game developers has been lack of raw memory bandwidth performance (ie, being unable to do stuff they can do anywhere else, even though the GPU itself can easily handle the task).

I suspect this is also why the iPhone 6S switched to a PCI-E SSD for flash instead of an SDIO/eMMC store like most devices use, just so high performance apps (such as games streaming in assets during runtime) don't choke the phone.

http://www.anandtech.com/show/9662/iphone-6s-and-iphone-6s-p...

According to them with an unoptimized benchmark (doesn't do queue depth >1 yet like desktop benchmarks do; required for real SSD benchmarking), Apple basically doubled the performance of the flash IO.

Intel's L3 cache is for CPU only, Apple's is propably shared with the GPU. Also some Intel CPU's have 128MB of "L4" cache to primarily speed up the GPU.

It isn't for CPU only, Haswell and up GPUs can zero-copy their command buffers out of it (thus making a large number of GPU compute situations "free"); they can't usefully use such a small amount of L3 for texture and framebuffer stuff (not like the highly optimized prefetch and caching systems in Radeons and Geforces can; that is sometimes a work of art).

But yes, I highly suspect the bigger L3 on these serves the same purpose as the L4 on Crystalwells.

Yea, I guess the interesting question is why desktop CPUs have relatively so little (I suspect the answer is Intel trying to price differentiate their Xeon chips, but who knows)

Do desktop systems have faster RAM? That would make the cache less important if so. Just a random guess.

Yes, they can.

Modern mobile devices have single or dual channel, DDR3L-800 through 1600. I'm not seeing any relevant mobile devices still shipping with DDR2, although sub-$100 tablets and anything that is a router still do.

Modern desktops and laptops are dual channel and DDR3-1600 and up, or now that DDR4 is a thing, DDR4-1866 or up.

Gaming machines/high performance workstations are DDR3-2133 and up, or with DDR4, 2400 and up is becoming popular.

LGA-2011-based stuff is quad channel, and LGA-2011 stuff can be multiple socket (its a waste not to populate dual socket E5s with at least 8 sticks).

Cache is a way to enhance performance in a way that can come at a relatively modest cost in power if not in chip area. 8T SRAM cells don't use much power statically, increasing size increases wire capacitance but you aren't switching any more transistors than with a 4mb cache save an extra level of muxing.

Perhaps they need it to handle the 12-megapixel photos and 4K video.

Those are basically streaming, I doubt it.

Oh, so when you take photos and record videos, the data doesn't touch the CPU?

It touches the CPU but it doesn't need to be cached. The CPU loads it, computes on it, then sends it on its way. Hence a 8mb cache wouldn't work any better than a 4mb cache or even a 1mb cache. It's the changes to the storage bandwidth that reflect the better camera.

The uncompressed data generally doesn't

And the Image Signal Processor doesn't share the L3 cache?

The A7 broke new ground by having an unprecedented 4mb L3 cache, which is what helped give it such amazing performance. (See Anandtech review of iPad Air/iPhone 5S)

Wonder why they have multiple power management/amplifier modules ? : 1. Apple/Dialog 338S00120 Power Management IC 2. Qualcomm PMD9635 Power Management IC 3. Texas Instruments 65730AOP Power Management IC 4. Avago ACPM 7714 Multimode Power Amplifier 5. Avago AFEM-8030 Power Amplifier Module 6. Skyworks SKY77357 Power Amplifier Module (likely an iteration of the SKY77354) 7. Skyworks SKY77812 Power Amplifier Module

Well, the first three you mentioned are for providing power to other chips, the last 4 are RF amplifiers, they aren't really related.

Why you need (or want) multiple power management ICs: they are likely powering separate zones of the board which may have very different power requirements, e.g. need different voltages, need to be able to power up or down separately, or need particularly clean power.

Why you need multiple RF amplifiers: Almost all phone today run on many different cellular frequencies and protocols, a quick look at the specs indicates the iPhone 6 supports: 800Mhz, 850Mhz, 900Mhz, 1700Mhz, 1800Mhz, 1900Mhz, 2000Mhz, and 2100Mhz along with various different signaling schemes. You can't handle all that in a single RF pathway.

>need to be able to power up or down separately

Need to be able to power on the Data, MIC and Camera per the Court Order without waking up the rest of the phone :)

I think because every LTE band you want to support requires its own front end with its own power management. The iPhone 6s is as close to a universal SKU as you get with LTE so they pack lots of those.

> This year Apple did multi-country launches ... so no more driving down to the US and queuing for hours to be sure of getting one or two.

What is Apple's iPhone 6s release schedule?

Apparently, they have already released it in the countries other than the US, but I still can't see any information online regarding where it was released and where it's going to, next.

Released in "Australia, Canada, China, France, Germany, Hong Kong, Japan, New Zealand, Puerto Rico, Singapore, the UK, and the United States."

http://imgur.com/wvTtvNu

http://www.macrumors.com/2015/09/24/iphone6s-launch-kicks-of...

Thanks! Any info on the next wave of country releases?

Today's press release[1] announced Oct 9 as launch date for 40 more countries. Expected to hit 130 countries by end of the year.

[1] http://www.apple.com/pr/library/2015/09/28Apple-Announces-Re...

Reply on news.ycombinator.com