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ARM Processor - An Introduction

We all have come across RISC architecture for computer processors. RISC stands for Reduced Instruction Set Computing. ARM, standing for Advance RISC Machines, belongs to the RISC family of architecture. As the name suggests, it requires very few instructions and transistors and comes in smaller size. Thus, it fits perfectly for low power, smaller size devices.

Arm holding develops this architecture and licenses it to other companies who design their own product based on this architecture. The products can be System on Chips, System on Modules that incorporates memory, interfaces, radios etc.

The main features of ARM that we need to be aware of are

ARM Processors are based on RISC architecture. But based on the requirements of the embedded systems, some amendments to the RISC architecture are made.

ARM Processors follow Load and Store type architecture where the data processing is performed only on the contents of the registers rather than directly on the memory. The instructions for data processing on registers are different from that access the memory. The instruction set of ARM is uniform and fixed in length. 32-bit ARM Processors have two instruction sets: general 32-bit ARM Instruction Set and 16-bit Thumb Instruction Set. ARM supports multiple stages of pipeline to speed up the flow of instructions. In a simple three stage pipeline, the instructions follow three stages: fetch, decode and execute.

ARM Versions

ARM architectures comes with different versions such as ARMv1, ARMv2, etc. Each of the version has its own advantages and disadvantages. In the embedded product development segments, we commonly come across processors from ARM Cortex family. ARM cortex family processor is based on ARMv7 architecture.

Within each of the architecture, there are 3 profiles that we need to know about.

1. A Profile – Applications

→ High Performance

→ Capable of running complex OS such as Linux or Android

2. R Profile – Real Time

→ Focus on systems performing real time operations

→ Targets networking solutions or embedded control systems

3. M Profile – Microcontroller

→ Focus on smaller Low Power Devices

→ Popular in IOT space

In today’s complex solutions, we can find one end devices comprising of all the above 3 profiles. The main processor would be A Profile, whereas, the networking chip would be based on R Profile. The device would also comprise of some low power chips based on M Profile.

We shall discuss in detail on the ARM family and versions in the upcoming blogs. In case of any queries, please feel free to get in touch with us.


Sarvesh Rajagopal

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