Two weeks ago, AMD announced that its ambitious Project Skybridge, which was intended to provide a unified platform for x86 and ARM chips, had been unceremoniously canceled due to minimum vendor interest. Given that the company had delayed its first Cortex-A57 ARM CPU and follow-up custom ARM architecture, this seemed to make sense. Rory Read may have talked up the idea that ARM would account for a huge swath of the dense server market by 2017, but it was never clear that this was actually happening. Now, however, a new set of rumors has suggested that the reason was more prosaic. After agreeing to work with Samsung on 20nm, GlobalFoundries may have torn up its own 20nm roadmap — leaving AMD without a platform for its processor.

The rumor from BitsandChips.it (Google Translated version available here) is that GlobalFoundries decided to kill its 20nm process, leaving AMD without a vendor partner for its HSA-capable 20nm iteration of Jaguar. If you recall, one of the major features of Project Skybridge was supposed to be platform compatibility with its ARM efforts. When AMD announced this in 2014 it was an ambitious move, but also one that made some sense: HSA would come to AMD’s lower-end parts, the ARM and x86 common platform would open the door to a standardized socket for all AMD hardware, and Sunnyvale would have a fast 20nm follow-up to the 28nm Cortex-A57 “Seattle” core that was originally supposed to debut in late 2014. So could GlobalFoundries have effectively killed AMD’s ambitions?

A complex situation

A quick check of the Wayback Machine reveals that GlobalFoundries has indeed killed t its 20nm product division. As recently as April 10, 20nm LPM was still listed as a future node that would be available for customer designs. The original roadmap that GlobalFoundries laid out, pre-Samsung partnership, called for a 20nm planar node followed by a transition to a hybrid 20/14nm process the company dubbed 14nm-XM.

Given that AMD had moved its socketed Kabini processors over to GlobalFoundries, it’s entirely possible that the design firm originally planned to build Skybridge at GF as well. Once the deal with Samsung was signed, GlobalFoundries may have been under contractual obligation to devote most of its resources to bringing up 14nm capacity in order to serve as Samsung’s second source.

I’m dubious, however, that the decision to axe Skybridge was entirely driven by GlobalFoundries’ 20nm cancellation. What’s far more likely is that GF would’ve been willing to build out 20nm capacity for AMD, provided AMD was willing to front the cost of doing so. AMD, meanwhile, has made it perfectly clear that it isn’t interested in buying custom silicon lines from foundries — so much so that it put a slide in its Analyst Day deck noting that it would no longer pay other companies to build out custom production.

If AMD didn’t want to pay GlobalFoundries for an exclusive process node, it could theoretically have taken the chip design to TSMC. Sunnyvale did this once before, when GF couldn’t build its Krishna and Wichita APUs (these parts became Kabini and Temash). The decision to redesign the hardware, however, pushed introduction dates back a full year. Taking Skybridge to TSMC means ramping multiple designs on the short-lived 20nm node — designs that would be pushed back into competing with Zen and possibly K12 depending on bring-up timing.

GlobalFoundries node cancellation could also explain why AMD paid no apparent penalty for failing to buy as many wafers as originally forecast. Normally, failing to purchase its expected quota of silicon wafers from GlobalFoundries would incur a penalty, but AMD didn’t pay one in 2014.

The bottom line is this: Whether GF’s 20nm cancellation killed Skybridge directly or not, there’s precious little evidence that the industry is clamoring for a dual ARM/x86 solution on a common 20nm platform. As fond as I was of AMD’s low-power cores, it didn’t necessarily make sense to do a 20nm die shrink of the technology if the common platform was a hybrid architecture only a handful of vendors were interested in buying.