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Parted partners reconcile in multicore drive

Posted: 16 Nov 2007 ?? ?Print Version ?Bookmark and Share

Keywords:Power.org? multicore processor? SoC design?

IBM Corp. and Freescale Semiconductor Inc., which had a parting of ways after co-developing the Power microprocessor in the 1990s, have reunited their efforts through the Power.org group. One of the biggest hurdles the companies face is whether they can resolve their longtime differences as to which on-chip bus they will ride into the multicore future. Freescale is holding close to one of the more promising candidates, its own CoreNet technology.

Although IBM has asked for technical details of the on-chip fabric, Freescale has not been forthcoming. A Freescale source who asked not to be identified said that there is a debate within the company about whether it should keep the CoreNet technology proprietary, license it to IBM or open it up to all comers through Power.org.

Freescale considers its interconnect a key ingredient in a family of multicore processors that it eventually will roll out across all of its chips, starting with 45nm products next year. The bus can stretch to data rates beyond 1.8GHz, linking as many as 32 cores.

"At the end of the day, we think our multicore architecture could help us get performance boosts of 2-3x," said Jeff Timbs, director of marketing for Freescale's networking group, who has been evangelizing the architecture.

To each its own
A Power.org technical committee was set to issue a report concluding that there is no immediate hope of creating a standard on-chip bus for the fledgling Power community, because all the players involved seem to be going their own way.

In addition to Freescale, with its CoreNet, Applied Micro Circuits Corp. (AMCC) has licensed the ARM AXI bus, and startup PA Semi Inc. has its own Connexium interconnect.

IBM is said to have delayed development on the next-generation of its Core Connect, the PLB6, hoping the issue would be resolved. The current PLB4 version is apparently adequate for any 2008-class designs the company has in the works. But IBM will likely reactivate the PLB6 design next year if no other alternative emerges.

All the players recognize the future is moving to SoC designs that use multiple cores, accelerators and other blocks. They want to share resources as much as possible, since their architecture lacks the economies of scale of the competing x86 and ARM worlds. And they know it would be easier to attract third-party chip designers if they had a common, open interconnect.

Beyond that, little is known about the exact nature of the debates inside Freescale and IBM or the talks between them. But it's clear the matter needs to get resolved soon.

"You would think Freescale would be more open!after all, standards are what Power.org is supposed to be about," said Tom Starnes, a longtime embedded processor analyst and former Motorola employee. "This sounds like the old Motorola semiconductor group !that has become Freescale!is afraid of enabling a competitor," said Starnes, principal of Strategy Sanity.

"There are so many things that go into a complete chip that the details of the on-chip interconnect might not make that much difference," he added.

The Power microprocessor architecture is plagued by too many on-chip buses. Each Power.org member has its own route to a multicore future.

Starting over
IBM and Freescale had a painful parting of ways several years back, and reuniting is not easy. Their PowerPC aspired to rival the x86 in mainstream computers when it was conceived in 1991, but after a few years it became clear Apple would be their only child. When Apple CEO Steve Jobs publicly announced in 2005 that the company was switching to the x86, it was a body blow for the Power duo.

From 1998-2006, IBM and Freescale went their separate ways. IBM focused on its Power servers, sold its embedded Power business to AMCC and continued to provide Power cores to all comers. Freescale continued to develop embedded versions of Power for its own use.

But maintaining leading-edge fabs and design capabilities to keep pace with Intel Corp. is an expensive business for Big Blue. IBM has always needed help funding that effort. So it got quite a boost when Microsoft, Nintendo and Sony all agreed to use Power-based chips for their current generation videogame consoles.

In March 2004, longtime IBM veteran Nicholas Donofrio made a speech to IBMers calling for them to take a cue from the rising world of Linux and open up the Power architecture. A group of managers responded, creating Power.org in 2004. Freescale joined in 2006, and the group held its first technical conference!the Power Architecture Developer Conference!as a sort of recommitment ceremony.

It was not a big affair, about 385 people. One noted it was little more than a public version of the annual Power partners meeting the group likely would have convened in Austin, Texas anyway. The members just opened the doors this time, hoping for more press coverage and the possibility some new customers might stroll in.

In fact, Power.org is not really an open development group in the spirit of Linux or GNU. IBM owns the intellectual property in the Power architecture, and only IBM and Freescale are members of the Power Architecture Advisory Board, which sets the technical direction for the ISA.

AMCC lacks an expensive architecture license from IBM to gain access to the Power Architecture Advisory Council (PAAC). PA Semi has a license because it needed to change the ISA to tweak the architecture for its 2GHz, 13W design, but it lacks the pricey patent cross-license with IBM that's required to be a PAAC member. So it seems Freescale is not the only company that is a little less than wide open these days.

Sounding board
Thus, Power.org is to some extent a sounding board for Power users and a marketing vehicle to the broader community. But it is also home to a fairly rich set of technical committees, overseen by Michael Paczan, an IBM veteran and former co-director of the Somerset lab where the PowerPC was born. Paczan effectively acts as a business and technology development manager for IBM's Power business and oversees the technical work inside Power.org, much of it driven by capable IBM middle managers.

Snapshots from the Power family's past: Long road from targeting mainstream computing in 1990s to today's focus on embedded and IBM servers.

One subcommittee is defining a set of common debug standards badly needed by Power users and tool makers. Today, tool makers have different debug approaches for each version of Power, which adds to the cost and time required to complete system designs, said Chris Ng, an IBM manager who runs the Power.org subcommittee overseeing debug standards. The group may adopt the Nexus and Aurora standards used by Xilinx Inc., Ng said.

Another group is looking at SoC standards, including a common bus. It has also identified the need for common model standards for Power chips.

Yet another group will develop key virtualization technology for Power, the software that helps milk the most performance out of multicore chips. Obtaining optimal results will require support both in Power chips and in the embedded operating systems they use. So far, the embedded OS companies are mum about whether they will put that support in future products, said Hollis Blanchard, the IBM manager chairing that Power.org committee.

All of the work is critical for the long-term success of Power, but none of it will have an immediate impact. "It takes a long time before you get any advantage from some of these efforts," said Starnes.

- Rick Merritt
EE Times




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