ARM sort of dropped the introduction of the ARM Cortex-A7 processor core out of the sky a couple of weeks ago (see “ARM drops Cortex-A7 core on unsuspecting market, devastates low-power SoC and application-processor landscapes. What’s it all mean?”), so you might be wondering about its place in the ARM Cortex-A series pantheon.
I was able to spend a few minutes discussing the Cortex-A7 core with Brian Jeff, a Product Manager at ARM, and he told me several significant things you need to know about the ARM Cortex-A7 core when making a processor core selection for you next SoC design:
- At the same clock frequency, the ARM Cortex-A7 delivers 20% more performance than the ARM Cortex-A8 but at 40% of the power consumption.
- The ARM Cortex-A7 consumes approximately 0.45 square millimeters when implemented in a 28nm process technology and should run at clock rates exceeding 1GHz.
- The ARM Cortex-A7 processor core is architecturally identical to the ARM Cortex-A15, which is why it can work in big/little combinations with its more powerful sibling.
- When implemented in big/little combinations with ARM Cortex-A15 processor cores, there should be equal numbers of ARM Cortex-A15 and ARM Cortex-A7 processor cores.
Jeff believes that low-end smartphones that become available in the year 2013 will offer the same features as today’s smartphones but will cost less than $100 without a carrier subsidy. You don’t need CPUs operating in excess of 1GHz for voice calls and SMS messaging so the available performance in smartphones needs to be quite plastic. Hence the movement towards big/little processing that incorporates a big, powerful processor core and a smaller, less power-hungry processor core. Already, the android OS can easily switch system operation between two (or four) such cores. Significantly, tight coupling between such cores with cache coherency allows the context switch between the big and little cores to take as little as 20 microseconds.