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Cortex-R82 Brings Linux to SSDs

September 29, 2020

Author: Bob Wheeler

Compared with mobile devices, real-time-system de­signs have long product cycles. Arm’s Cortex-R line re­flects that slower pace, with each generation spanning about four years. The new Cortex-R82 marks an important milestone for the line, introducing both a 64-bit architec­ture and high-level operating system (HLOS) sup­port. Arm posi­tions it for computational storage, providing next-generation stor­age controllers with an up­grade from Cortex-R8. The new R82 also brings to storage the Arm v8-R in­struction set, as the first CPU to imple­ment this ISA targets functional safety requiring lockstep operation (see MPR 10/3/16, “Cortex-R52: Safer Real-Time Control”).

The R82 includes many important changes from the R8, which was a modest upgrade from the Cortex-R7 introduced nine years ago. It allows up to eight CPUs per cluster, double that of its predecessor. The R82 expands physical addressing to 40 bits, enabling up to 1TB of DRAM, which compares with only 4GB for its predecessor. It’s also the first R-series core to provide an optional Amba Chi cluster interface, letting designers mix A- and R-series clusters in a cache-coherent configuration.

From a software perspective, what makes the R82 unique in its line is the optional memory-management unit (MMU), which enables virtual memory and HLOSs including Linux. Because it still offers memory-protection units (MPUs), a single cluster can dynamically mix real-time cores running a simple kernel (or RTOS) and application cores running Linux. As the cost of developing storage controllers in advanced process nodes continues to rise, Arm envisions customers taping out a controller chip that can serve multiple applications. For example, one SoC could handle high-performance SSDs using only real-time operating systems, and it could also handle computational-storage drives (CSDs) running a mix of HLOS and RTOS cores.

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