anon (spam.delete.delete@this.this.spam.com) on November 1, 2016 4:22 pm wrote:
> Of course it's not always a safe assumption.
>
> But in this case where the design target (device and therefore power budget)
> was known years in advance, it's not a completely new architecture, they've
> done a CPU on the same process before so none of the great unknowns apply.
>
> I'm sure they would have realised soon enough if they overshot their target massively and then went
> for higher frequencies and lower voltages to use that headroom and stay within the power budget.
>
> Really there's only two things we'd need to know:
> 1. tau vs voltage for 16FF+
> 2. stock voltage for the A10.
>
> Of course that still won't quite be the maximum but we'd have a minimum figure as to how far
> you could push it with a desktop/server power budget (essentially unlimited in this case).

Since we don't have access to that information, we have to use alternative methods.

We can guess at some level of the TARGET upper frequency by assuming that the A9X:A9 frequency ratio will carry over to the A10X. Is this a perfect assumption? Of course not, but it's the best we have. This assumes, essentially, that the A10X is the design target frequency/power, and the A10 is frequency downscaled version (perhaps with tweaks like lower power transistors used in a few places that were considered safe.)

If we do this, we get an assumed A10X 16FF frequency of 2.25/1.85*2.35=2.85GHz.
Throw in a free frequency scaling of 20% as TSMC has offered up for 10nm and we get to 3.4GHz. (Obviously that frequency scaling is making assumptions about both transistor performance scaling and RC scaling. You can quibble about this, but let's assume that TSMC are speaking honestly, not making legally correct but technically useless claims --- they are, after all, in the business of satisfying a wide customer base rather than pissing them off.)

As I have said before, these are not outrageous assumptions, but they get us to an impressive frequency. Not 4GHz, sure, but not bad.