ARM announces Cortex-A7 MPCore and big.LITTLE processing

ARM today announced Cortex-A7 MPCore processor, that features better performance, considerably lower power consumption and smaller size than existing Cortex-A8 designs. The new processor can be paired with Cortex-A15 MPCore for so called "big.LITTLE processing". Combining two processors into one system on a chip allows operating system to switch between Cortex-A15 for maximum performance, and Cortex-A7 for low-power operation. ARM estimates that using companion Cortex-A7 CPU to run less intensive computing tasks may extend battery life up to 70%. In related news, Freescale announced that they licensed ARM Cortex-A7 and Cortex-A15 MPCores for future generations of i.MX products. Other ARM partners, supporting Cortex-A7 design, are Broadcom, Compal, HiSilicon, LG Electronics, Linaro, OK Labs, QNX, Redbend, Samsung, Sprint, ST-Ericsson and Texas Instruments.

Cortex-A7 MPCore is an in-order dual-issue processor, that integrates from 1 to 4 CPU cores, shared L2 cache with snoop control circuitry, 128-bit AMBA-4 coherent bus interface, and system logic. Each CPU core has its own 32 KB L1 cache, integer unit with virtualization support and Large Physical Address Extensions, and Neon/Floating Point Unit engine. When manufactured in 28nm technology, the processor can reach frequencies higher than 1 GHz, and occupies only 0.45 mm2 in single-core configuration. Compared to Cortex-A15, Cortex A7 has 2 - 3 times lower performance, but offers 2.3 - 3.8 times better power consumption.

Cortex-A7 MPCore, combined with Cortex-A15 processor, can be used as a "big.LITTLE processing" system. Cortex-A15 may have from 1 to 4 CPU cores, although ARM recommends the same number of cores on both processors. In this system, a special software switcher is used to switch between Cortex-A7 and Cortex-A15 MPCores depending on load. During the switch, one processor saves internal state, and transfers it to the second processor, where the state is restored. After that the first processor powers off. The whole process takes less than 20000 cycles, or 20 micro-seconds on 1 GHz processor.