There will be no PA Semi designed ARM core in apple tablet....

....unless they are planning to release the tablet in 2012 (do read on for why)....

I've been reading the hype regarding Apple's tablet computer thingummy, and there seems to be a zeitgeist of opinion that Apple's latest gadget will contain an ARM compatible CPU designed by the team they gained after acquiring PA Semi in April, 2008.

This article claims that a device will appear at the beginning of 2010, and that during its development (over a 4 year period) Apple had considered use of the Atom processor, rejecting it on grounds of power consumption. To bridge this gap, it is claimed, Apple bought PA Semi at the end of April 2008, in order for Apple to have an in-house capability for System On Chip (SOC), as well as to allow it to differentiate it's technology from everyone elses.

At the moment, iPhone teardowns reveal exact component specs, allowing the revelation of every piece of hardware (and, subsequently, the processor). This is how we all know that the iPhone 3GS contains an ARM Cortex-A8 (along with the Apple Job adverts specifying knowledge of the ARM NEON instruction set - Cortex-A8 is currently the only ARM silicon that has a NEON pipeline attached). Apple could - by designing its own chips - keep the content completely secret - something you cannot do when you buy an off-the-shelf component.

Right now, talk of this tablet computer has people speculating that it will contain PA Semi's first CPU design for Apple.

I think this is unlikely.

Apple acquired PA Semi in April 2008. It takes nearly 2.5 years to bring a new microprocessor - from initial spec, to releasable quality - into a form where you could conceivably manufacture it, having validated it enough.

Various stories have emerged over the last year or so speculating that Apple will be using the PA Semi team to design an ARM CPU. Who knows if this is true, or if any of the rumours about this tablet are true?

PA Semi's last exposure to ARM CPUs was when some of the team worked on the StrongARM processor at DEC. This was an ARMV5 architecture processor, a very different beast to todays ARMV7 processors. Time has moved on, and there is a whole different architecture to learn, with many new features. Just to learn this new architecture would take an architect 6-8 months to master, during which time they would model some of the micro-architectural ideas they have floating in their head. This could happen in parallel with some Register Transfer Level (RTL) trialling, but only in a behavioural sense. By the time PA Semi has done all of this, it brings us to the end of 2008, with nothing more than an understanding of the architecture, and various models of the micro-architecture of the CPU.

Even with an installed product design team working on concepts and prototypes for the actual look and feel of the hardware (remember, they'd been working on this for nearly 2.5 years, if the story is true), the actual silicon inside is a very different beast. Assuming that work began on the actual design of the CPU, it would still take nearly two years to get the core to a state where ARM would sign off on their architectural compliance (if, indeed, the rumours of an ARM compatible CPU design are true). This takes us to the end of 2010 for Apple to have bespoke, manufacturable Silicon.

So no, the timescales are all wrong. And remember, the task above just relates to designing the CPU - it doesn't include the time taken to design a SOC around that CPU. They may have access to various designs already, but if they are going to the trouble to work on a bespoke CPU, then they won't at the same time go and take some other SOC - htey'll build a new one.

Their recent share interest in Imagination Technologies graphics processor design house indicates that Apple will be using their technology in their SOC, but without an in-house design for a CPU, where will they get that from?

To design a SOC - into which they would drop an ARM CPU - they would need an ARM CPU license. When they just purchase an off-the-shelf chip package - like the ones they get from Samsung - they do not need this, because Samsung are the ones who have taken out the ARM CPU license and manufactured a SOC with it.

I think the likely first set of tasks that the PA Semi team will be doing is to create a SOC using a pre-existing set of designs that they would license, so as to keep the flow of products emerging from their portfolio.

There are interesting times ahead, but I don't believe that Apple have a custom ARM CPU ready to go for an early 2010 release. If this even has a shred of truth to it, expect an early 2011 release for anything like that.