Cortex-A15 to A5: Software compatibility from Superphone to Feature phone

It was always about the code (and where it would be used!)

When I was a software developer I would often find that the project team I was in would try to guess how many devices the code would eventually run on. So at the launch of the Cortex-A15 last week one of the main points that hit home for me was just how wide the spectrum of power and performance points the Cortex-A family of processors could cover - from feature phone to superphone, tablet to DTV, home server to web server etc. This means that a developer could now find their software running across a huge range of devices in the future.

So is it the same software?

Absolutely. Cortex-A15 is based on the same ARMv7A architecture that the other Cortex-A processors use, therefore allowing the exact same application code to run on all of them, from a Thumb-2 optimized Dalvik virtual machine to Flash 10.1 binary to multi-threaded VP8 NEON code, whether on Cortex-A5 to Cortex-A15. Either way consumers will be able to enjoy their favorite app store downloads without requiring developers to open up their source code again.

So you said application code is compatible, but what can you change?

So are there any major changes for software developers to take advantage of? Well for some developers the answer is yes. Cortex-A15 has a couple of new major features to enable its use in new markets. The vast majority of developers won't even have a need to know about these, but operating systems and low-level code may want to exploit them:

• Large Physical Address Extension (LPAE) — this allows Cortex-A15 to address up to 40-bits (1 terabyte) of physical memory. We've already implemented the patches for Linux and will be posting these any day now.
• Hardware Virtualization — this allows the support of multiple software environments to run in isolation from one another, without the software changes previously needed with para-virtualization techniques used in Cortex-A5, A8 and A9. Business and personal phone on the same device anyone?

So what's next and how do you find out more?

We will be releasing more detailed specifications, tools and models very soon (within one month), and we're just about to submit our Linux patches upstream. Feel free to check them out but, if you're an application developer, the potential number of devices your code could run on just got a lot bigger with no extra effort needed from you.