Brief analysis of ARM core and architecture concepts and their relationship

ARM products are becoming more and more diverse, and the names are also increasing. Many friends ask: What do ARM cores and architectures mean? What is the relationship between cores and architectures? For example, what does the ARMv7 architecture refer to?

1. ARM core: From ARM7, ARM9 to Cortex-A7, A8, A9, A12, A15, and then to Cortex-A53, A57, etc., in short, different versions of ARM have different ideas. For example, Cortex A8 and A9 designed for high speed are both ARMv7a architecture; Cortex M3 and M4 are ARMv7m architecture; the former is the core, and the latter is the architecture of the instruction set.

2. ARM's architecture is based on the RISC instruction set, and its core is only the basis of the hardware architecture that implements this instruction set. It is a subset of the Thumb-2 instruction set architecture (ISA), including all basic 16-bit and 32-bit Thumb-2 instructions, Harvard processor architecture, and can execute instruction fetch while loading/storing data, a three-stage pipeline with branch prediction, etc.

3. It's like you build a house. At the beginning, it's popular to build a bungalow because of the low level. This is an architecture (V5T). Then you can design a style with a separate bathroom for this bungalow architecture. This is called the ARM7 core. Then other people (chip design companies) who want to build a house will buy your blueprint to build it. Then after a while, some people think that a separate bathroom is not enough, and they also want a small yard! Well, then ARM will meet your requirements and release a style with a small yard (ARM9).

After a long time, the architecture of this bungalow has been changed and changed according to everyone's needs. Later, ARM found through research: Now everyone's ability to build houses has increased dramatically (including technology, design ability, clock frequency), and it is not enough to build this bungalow! Well, in order to keep these designers idle, ARM launched a style of two or three-story buildings. Because this is completely different from the design structure of bungalows, it is called a new architecture (ARMv6). Similarly, ARM also prepared styles with swimming pools and garages for everyone (ARM11). Well, continue to change and change, and later everyone has begun to have the ability to build buildings with more than ten floors. ARM has released a new style (ARMv7 architecture) as always. At this time, ARM feels that the previous names are too rustic, such as ARM5, ARM6, ARM7—both ugly and hard to remember. I want to give it a name that looks awesome, so that at least I can be considered a person who can design skyscrapers. So the subsequent cores are called Cortex.

The name change is only part of the story. With the release of this architecture, ARM discovered that the buildings built using our blueprints were only used as residential buildings. What was the point of residential buildings? They were economical (low power consumption). Now it is different. The buildings built using our blueprints can be used not only as residential buildings, but also as military bases and high-end office buildings. In the past, only Intel could design these high-end buildings! In order to meet these different needs, ARM divided the styles designed using this architecture into three series (M series, R series, and A series).

The M series is designed for residential use, because ordinary people want to be economical, so this type of design is designed to be about ten stories high (low power consumption); the R series is designed for military bases, and this type of building is not designed to be high - about ten stories high, but the key is to have the ability to respond quickly to special situations (fast interruption); finally, the A series is for business leaders, so of course it has to be high-end and classy, ​​with high performance and all kinds of LED light shows.