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ARM8 Architectural Overview

Integratable, Process Portable, High-Performance RISC Processors


Advanced RISC Machines Ltd (ARM) designs and licenses a family of general purpose 32-bit RISC microprocessors. The ARM8 architecture will extend ARM's product portfolio by filling the gap between the elegantly minimal, embeddable ARM7 RISC cores and the very high performance StrongARM processor.

As a result ARM offers a completely software compatible solution across the entire performance range. Through ARM's unique partnership model, designers now have access to a broad spectrum of application knowledge and experience at each performance level.

ARM recognizes that various market segments require very different optimizations in architectural implementation. For example, mobile communication systems require consistent real-time response to external events, portable computing requires strong performance with low power consumption and advanced digital multi-media systems have massive processing requirements. ARM meets these needs through the development of architectural modifications and extensions, while maintaining complete compatibility.

Available in 2H96 from ARM's licensed partners, the ARM810 will be the first product to implement the ARM8 architecture. Designed to a process portable 0.5 micron rule-set, ARM810 can be implemented as an embedded core within an application specific design or as a stand-alone microprocessor.

How the ARM8 Architecture Extends the ARM Processor Family The new ARM8 architecture is aimed at systems which will benefit from a high performance cached processor, but are still sensitive to system power consumption and cost. Target applications include: high-end mobile-computing, second generation PDAs and multimedia applications.

Most high integration, real time, applications are best addressed by the ARM7TDMI, which, with the Thumb code compressing extension, is class leading in terms of cost, performance and area efficiency. ARM8 will step in where even greater performance is required. ARM8 is a major architecture enhancement having the potential to deliver 80 MIPS of performance (3.3V, .5 micron) to those applications requiring it without any decrease in power efficiency. Where less than 40 MIPS is required, ARM710 remains the general purpose processor of choice.

ARM General Purpose, Packaged Processors Compared

ARM710 ARM810 StrongARM
MIPS (Dhry 2.1) 36 80 > 160
Power (W) 0.5 0.5 0.5
Supply Voltage 5.0 3.3 1.5
Process (microns) 0.6 0.5 0.35
Cache Size 8KB 8KB TBA
Pipeline stages 3 5 5

ARM8 Core Micro-Architecture

The most significant change to the ARM8 core when compared to other ARM processors is the extension of the pipeline into five stages. This results in execution being is spread over more cycles, reducing the amount of work done at each stage and thus allowing higher clock rates. Performance is further enhanced by ensuring that all parts of the processing and memory systems spend as little time as possible waiting for data to arrive and so operate continuously. The following diagram compares the ARM8's 5 pipeline stages to the 3 stages found in the ARM7 core.

ARM7 and ARM8 Pipeline Stages Compared

ARM7 - Fetch, Decode, Execute

ARM8 - Fetch, Read, ALU, Memory Write

In addition the shifter and adder now operate in parallel rather than in serial, further reducing core cycle time. The pipeline and other architectural changes have reduced the CPI of the ARM8 core to 1.43. The following diagram shows the ARM8 core micro-architecture.

ARM8 Core Micro-Architecture Diagram

see paper or Word original


The ARM8 is ideal for mobile, hand-held and multimedia applications that require high performance and low power consumption at modest system cost. Moving from a three to five stage pipe, with other architectural enhancements, has resulted in double the performance, but at no decrease in power efficiency. This, combined with the ability to integrate the ARM8 with a wide variety of other peripherals and a proven design environment, provides a unique level of design flexibility.

The first ARM8 based product, the ARM810 will be available in summer 1996. It will be a cached, general purpose system CPU and be made available both as a packaged microcontroller and as an integratable macrocell for custom designs. ARM8 based designs will fill the gap between the elegantly minimal, embeddable ARM7 RISC cores and the very high performance StrongARM processor.

The above is a Press release from ARM Limited, November 1995