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Comment by endorphone | Hacker News Reader

This sort of very specific benchmark is never particularly useful as single instructions on one architecture or another can yield magnitude differences.

The T2 security coprocessor in the Mac -- a minimalist ARM implementation to manage a few very specific parts of the Mac -- does HEVC encoding (e.g. dramatically more complex than decoding) thirty times faster than the Intel chip it sits beside. I can't say it's a 30x faster chip, however.

High TDP Intel chips definitely are much more powerful than Apple's A-series chips right now. It will be interesting to see what Apple can do with a larger power profile and active cooling, however. That's theoretical, but they should have an enormous amount of headroom to exploit.

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It is important to realize that the T2 coprocessor is just an A10 cpu which didn't meet the binning criteria to be included in an iPhone 7 or 2018 iPad.

It happens to have hardware acclerated HEVC encoding.

While it's clearly re-purposing of their core IP, I think the A10 assumption was a mistake on the part of iFixIt, who then corrected their mistake realizing the core size was not the same (and it definitely isn't just binning). The HEVC performance is still surprising though because they get much better performance out of the T2 (whatever its lineage) than they get out of a 6-core Intel processor, the Intel integrated GPU, or even the AMD dedicated GPU. That's the power of optimized silicon.

No, they said "some random chip" (just to the right of the T2) is too small to be an A10. [1]

I did once throw a photo of a mac motherboard into an image editor and estimated the T2 package dimensions. They were a very close match for the A10 Fusion, within the margin of error.

[1] https://pbs.twimg.com/media/DSk789lWsAUJ4Lp.jpg:large

But that mistake is what led to the otherwise completely uncited claim that it was a binned A10.

Clearly Apple copy-pasted their core, but the T2 serves such a novel purpose in the Mac, and has some unique performance requirements, that it seems very unlikely that they sourced it from the A10 reject bin. Much more likely they simply used of their ARMv8 cores with some custom IP particular for the Mac as they slowly moved the line to ARM. This is all just speculation though.

Here's the logic:

Tapping out a new SoC design costs Apple hundreds of millions of dollars and years of engineering time. Reusing those pieces of A10 silicon that had defects effecting only part of the chip is essentially free.

Every other SoC/CPU manufacture does this, sells the same piece of silicon at different clock-speeds or with half the cores disabled. The fact that apple typically doesn't do this binning actually puts Apple at a disadvantage cost wise.

> but the T2 serves such a novel purpose in the Mac, and has some unique performance requirements

Sure, but the performance requirements are all a subset of what the A10 can already do. There is no need for a large GPU like the A10 has, the T2 only drives a tiny, low animation display. Yet the GPU takes up ~35% of the A10 die. There is also no need for such powerful CPU cores.

If apple were designing a custom SoC for inclusion in Macs to meet those requirements, it should logically be much smaller than the A10.

Yet we have this T2 chip which is basically the same size as the A10.

Binning is actually the exception. You can't find binned Snapdragon 855s, for instance. Or most Intel chips. Rejects are generally destroyed.

When Apple moved to the T-chips they also moved several system management chips to it as well (e.g. copy-pasting the design alongside the A10).

Software on a general purpose CPU is great, but it simply isn't nearly fast enough for many system management functions. For >4GB/second DMA to go through it (for security oversight, encryption/decryption, etc), for instance -- that simply eliminates it from being a binned A10 at the outset, which was never designed around such a high performance need. The specialized display controller for the touchbar is absolutely nothing like the very purpose-developed display controller in the A10, either. These are all differences that would make it a terrible hack for them to use an A10.

Until we have imaging of the T2 innards we can't say, but I'd say with 99.999%+ certainty it is simply not possible for it to be a binned A10. An A10 single core integrated on some new IP (with purpose-suited blocks that perfectly fulfill their roles concurrent with the general processor), sure, but not an A10.

Hang on, why is there a HEVC encoder in the security coprocessor and not the graphics unit?

Because that's the name of the chip in the Mac that Apple developed in house. They had that IP hanging around and put it in the only place they could - the security coprocessor.

See sibling comment that the security coprocessor is a repurposed A10. And then to answer the next question, because the HEVC encoder for iPhones has been optimised, and they can likely just use the same code that already exists for iOS.

I have wondered whether they should be using the GPU in the A10/T2 too, instead of the Intel integrated graphics. Would probably perform rather well!

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