The ARM processor uses an approach known as a reduced instruction set. This approach provides many advantages for embedded systems requiring performance yet small power consumption.
The RISC, Reduced Instruction Set Computer was developed by the British company ARM Holdings - ARM standing for Advanced RISC Machine.
The ARM processor architecture has gained very wide acceptable for many embedded applications: ARM architecture processors being used in applications from smartphones to set top boxes and hard disc drives to games boxes.
The core IP is normally provided and embedded in chips manufactured by others and in this way ARM itself does not manufacture any chips of its own.

ARM history

The ARM processor arose out of the early personal computing technology.
The ARM processor was first developed by Acorn Computers for use as co-processor modules for the BBC Microcomputer developed in the 1980s and based around the 6502 processor chip.
The ARM technology was pushed forwards when Acorn wanted to address the business market.
To further this aim the company needed a number of second processors to be made to work with the BBC Micro platform. However processors such as the much more powerful Motorola 68000 and National Semiconductor 32016 could not be used with the 6502 because it was not sufficiently powerful for a graphics based user interface.
To achieve their aim, Acorn needed to develop a new processor architecture as all the other alternatives were not suitable. Although this seemed as if it would be a very large project, Acorn engineers discovered it was not as large as they had anticipated when they visited the Western Design Center in Phoenix. Here they saw the 6502 being updated by a single person company.
The Acorn engineers reasoned that they would not need a massive design team to achieve this.
The engineers set about developing an instruction set and simulating it on the BBC micro platform. The results were very encouraging and proved the concept.
With executive approval a small team was set up to develop the overall model in hardware and the RISC computer from ARM was started.

ARM basics

The key element of an ARM RISC processor that the reduced instruction set means that the processor can run on using fewer transistors and hence reduce current consumption.
The current consumption of any processor is a key attribute for many portable applications because it directly reflects into battery life.
Accordingly the ARM processor is well known for its low energy consumption and use in may portable devices.
Current versions use 32-bit instructions with 32-bit addressed 1 byte wide memory which is effectively reduced to just over 24 bit addressing due to 4 byte alignment, with some addressing reserved in byte wise allocation for Memory Mapped I/O, but accommodates 16-bit instructions for economy and can also handle Java byte codes which use 32-bit addresses.
The ARM processor architecture forms the basis of all ARM processors
Although the ARM architecture has evolved over time, it still adopts the same basic processor architecture adopted by the early ARM devices.

ARM architecture cores

ARMv132 / 26ARM1
ARMv232 / 26ARM2, ARM3
ARMv6M32ARM Cortex-M0, ARM Cortex-M0+, ARM Cortex-M1
ARMv7M32ARM Cortex-M3
ARMv7EM32ARM Cortex-M4
ARMv7-R32ARM Cortex-R4, ARM Cortex-R5, ARM Cortex-R7
ARMv7A32ARM Cortex-A5, ARM Cortex-A7, ARM Cortex-A8, ARM Cortex-A9, ARM Cortex-A12, ARM Cortex-A15, ARM Cortex-A17
ARMv8A64/32ARM Cortex-A53, ARM Cortex-A57
The ARM architecture has evolved over time. ARM architecture, ARMv7, defines the architecture for the first of the Cortex series of cores, for which there are three architecture "profiles".
  • A-profile:   Application profile relates to Cortex-A series.
  • R-profile:   Real-time profile relates to Cortex-R series.
  • M-profile:   Microcontroller profile relates to Cortex-M series.
The ARM architecture supports implementations across a wide range of performance points, establishing it as the leading architecture in many market segments. The ARM architecture supports a very broad range of performance points leading to very small implementations of ARM processors, and very efficient implementations of advanced designs using state of the art micro-architecture techniques. Implementation size, performance, and low power consumption are key attributes of the ARM architecture.
ARM developed architecture extensions to provide support for Java acceleration (Jazelle), security (TrustZone), SIMD, and Advanced SIMD (NEON) technologies. The ARMv8-architecture adds a Cryptographic extension as an optional feature. The ARM architecture is similar to a Reduced Instruction Set Computer (RISC) architecture, as it incorporates these typical RISC architecture features:
A uniform register file load/store architecture, where data processing operates only on register contents, not directly on memory contents.
Simple addressing modes, with all load/store addresses determined from register contents and instruction fields only.
Enhancements to a basic RISC architecture enable ARM processors to achieve a good balance of high performance, small code size, low power consumption and small silicon area.
ARM PROCESSOR ARM PROCESSOR Reviewed by Suresh Bojja on 8/29/2015 01:19:00 AM Rating: 5
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