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Cortex-A55 Improves Memory

June 6, 2017

Author: Linley Gwennap

As the little brother to Cortex-A75, the new Cortex-A55 CPU wants to tag along everywhere. Both support the same ARMv8.2 instructions and the new DynamIQ cluster architecture. They will appear together in Big.Little designs for high-end mobile processors. But the A55 will also step out on its own in lower-cost processors, replacing the popular Cortex-A53. If history is a guide, the smaller core will rack up more design wins than its more powerful sibling.

Even so, ARM decided the A55 needed to muscle up to keep pace with the A75. The new CPU delivers a 15–20% performance boost over the A53, primarily owing to memory-subsystem improvements. In fact, memory-streaming performance doubles compared with the A53. According to ARM’s measurements, memory (load/store) instructions comprise about 30% of most mobile applications, so improving the memory subsystem has a strong effect on overall performance. SPECfp in particular benefits from the memory improvements as well as enhancements in the floating-point units. These changes come with minimal increases in power and die area.

Cortex-A55 is based on the Cortex-A53 RTL, which ARM released three years ago as its first “little” ARMv8 CPU. The Cambridge (U.K.) team designed the A55 and shipped production RTL to lead customers in 4Q16; the first chips using Cortex-A55 should appear in phones around the end of this year. We expect most current A53-based designs will move to the A55 over time, although some low-cost products may instead move to Cortex-A35, which offers less performance in a smaller die area. Top A53 customers include mobile vendors MediaTek, Qualcomm, Spreadtrum, Samsung, and Huawei plus embedded vendors Broadcom and NXP.

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