@3dilettante
So now that we're looking at a 33% shrink for Xbox One S, any new thoughts on shrinking PS4 similarly? The power savings there seems to be about 30% for gaming, but I wonder if it wouldn't be that much for PS4 considering the GDDR5 bus wouldn't scale like that, and maybe it just wouldn't be worth it?
Size-wise, Polaris at 232mm2 shows how close a 36 CU GPU gets to taking up its perimeter with IO. By way of comparison, I did a quick MS paint check to see what amount of area would be taken out if I took out the Jaguar modules and the silicon between them from the Orbis die shot. That's about 25% of the die and it leaves behind ~250 mm2 as GPU, sundry controllers, and IO. Get a double-density GPU with twice the unit count and it seems like a decent fit to what Polaris is sized at.
If Sony opted for a GF/Samsung node for a shrink, it seems like it is possible to shrink the existing Orbis die so much that it would be smaller than Polaris 10--perhaps too small for the bus.
That's on a GF process, however. There's an apparently modest density benefit (power penalty, maybe) that might be how it gets a good density boost.
I'm uncertain about the apparent area scaling with the Xbox One S. In theory, it would be more primed to benefit from a shrink with a more compact memory bus and a lot of ESRAM rather than complex logic. Getting less than 50% scaling wouldn't be out of the question, although 30% on the face of it seems like something didn't scale as much, although a comparison with Polaris is not apples to apples due to the foundry difference.
Power-wise :
There were closer reference points for the PS4 since AMD disclosed comparisons between its GDDR5 subsystem and HBM.
Using the earlier speculation for Neo and Polaris:
https://forum.beyond3d.com/posts/1926535/
There, I assumed 110-120W for the Polaris GPU alone at its desktop base clocks, and handwaved some numbers like 27W for the GDDR5 bus and then possibly 10-15W margin to get around the peak draw of a launch PS4 running Killzone SF. The ASIC-only power draw appears to have been borne out in the end.
I'm not on firm ground as to what AMD's DDR3 bus would draw. I don't know if it would be twice as efficient as the Orbis GDDR5 bus, but if it were that would be ~14W and then maybe 10-15W for all other things non-SOC.
That does assume a more Polaris-like Neo implementation, which has some conflicting rumors about it.
For the Xbox If there's a ~30W baseline in non-SOC power consumption due to memory, VRM, and drive power consumption the APU portion's power scaling would look better than the 30% the whole-system measurements would indicate.
A purely shrunk PS4 seems like it might drop to close to the original Xbox One (maybe slightly lower?), if no further architectural changes occur. My other estimates were using something more Polaris-like.
