what does arm mean

arm can be considered as the name of a company, as a general term for a type of processor, or as the name of a technology. ARM is a company specializing in the design and development of chips based on RISC technology and is the world's leading provider of semiconductor intellectual property (IP). The ARM processor is the first RISC microprocessor with low power consumption and cost designed by British Acorn Co., Ltd. ARM technology has the characteristics of high performance, low cost and energy saving.

The operating environment of this tutorial: Windows 7 system, Dell G3 computer.

1. What is ARM?

• ARM can be considered to be the name of a company, or it can be considered to be the collective name for a type of processor, or It can be considered as the name of a technology.

• ARM is a company specializing in the design and development of chips based on RISC technology. It is the world's leading provider of semiconductor intellectual property (IP). As an intellectual property supplier , itself is not directly engaged in chip production, but transfers the design license, and the cooperative companies produce unique chips.

• The ARM processor is the first RISC microprocessor with low power consumption and cost designed by British Acorn Co., Ltd. The core of the ARM processor is unified, developed by Provided by ARM, and the on-chip components are diverse and designed by major semiconductor companies. This allows ARM to use different on-chip and on-chip components based on the same core when designing embedded systems. Assume , which has great advantages.

• ARM technology has the characteristics of high performance, low cost and energy saving. It has a leading position in the fields of smartphones, tablets, embedded controls, multimedia digital and other processors.

  
  

2. ARM core and architecture

Any arm chip is mainly composed of two parts :

arm core, Peripherals.

ARM core

arm core: The arm core mainly consists of: Register , Instruction set, Bus, Memory mapping rules, Interrupt logic and Debug components etc.

The core is designed by ARM and licensed to chip manufacturers for use by sales (ARM itself does not make chips). 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 processor (that is, the core) , and the latter is the instruction set architecture (also referred to as architecture).

Peripherals: Including timers, A/D converters, memory, I2C, UART, SPI, ROM, etc. Designed by each chip manufacturer and connected with the ARM core. Different chip manufacturers have different peripherals, thus forming a huge ARM chip industry in terms of quantity and specifications.

arm instruction set architecture

The design of the instruction set is the most important part of the processor structure. It is called ISA in arm terms. (Instruction Set Architecture).

The instruction set can be said to be the soul of CPU design. It is the spell that opens the Pandora's box of CPU. If we want to use the CPU, we can only operate the CPU through these instructions.

For a 32-bit CPU, these instructions are a sequence of 32-bit 01s. Different values ​​represent different machine instructions. The CPU hardware can perfectly parse and execute them. These instructions, such as addressing, operations, exception handling, etc.

When we play Honor of Kings on our mobile phones, we must know that every move we make is actually eventually translated into a series of machine instructions.

From the birth of the ARMv1 architecture in 1985, to 2011, the ARM architecture has developed to the eighth generation ARMv8.

Cortex-A32/35/53/57/72/73/77/78 all use the

ARMv8 architecture. This is the first ARM company to support 64-bit instructions Set processor architecture

Processor and instruction set architecture before ARM11

Before ARM11 chip , the corresponding architectural relationship of each chip is as follows:

After ARM11 processor and instruction set architecture

ARM11 chip Later, starting from

ARMv7 architecture, ARM's naming method changed.

The new processor family is named after Cortex and is divided into three series, namely Cortex-A, Cortex-R, and Cortex-M

ARM processor model

Cortex-A series (A: Application)

In response to the growing Consumer entertainment and wireless product designs for applications with high computing requirements, running rich operating systems and providing interactive media and graphics experiences, such as smartphones, tablets, automotive entertainment systems, digital TVs, Smartbooks, e-readers, home networks, home gateways and various other products.

Cortex-R series (R: Real-time)

Aimed at system applications that need to run real-time operations, for example Deeply embedded real-time applications such as automotive braking systems, power transmission solutions, large-capacity storage controllers, etc.

Cortex-SC Series (SC: SecurCore)

In fact, in addition to the above three series, there is also a Cortex-SC series (SC: SecurCore) that focuses on security. SecurCore), mainly used in government security chips.

The ARM11 series includes the ARM11MPCore processor, ARM1176 processor, ARM1156 processor, and ARM1136 processor, which are based on the ARMv6 architecture.

ARM Cortex-A5 processor, Cortex-A7 processor, Cortex-A8 processor, Cortex-A9 processor, and Cortex-A15 processor belong to the Cortex-A series and are based on the ARMv7-A architecture.

Cortex-A53 and Cortex-A57 processors belong to the Cortex-A50 series and adopt the 64-bit ARMv8 architecture for the first time.

In 2020, ARM recently released a new CPU architecture Cortex-A78, which is based on the ARMv8.2 instruction set.

3. What is SOC?

The full name of SoC is: System-on-a-Chip. The Chinese meaning is "Build the system on a chip".

SoC integrates many of the most critical components on mobile phones, such as CPU, GPU, memory, and That is to say, although it exists as a chip on the motherboard, it is composed of many component packages.

For example, what we usually call Qualcomm 801, Kirin 950, Samsung's exynos 4412, A6, etc. are just the general name for system components packaged and packaged (SoC). However, the contents of each package are different, and the reasons are also different.

#A classic ARM system-on-a-chip or so-called Soc contains many components, only some of which are directly derived from ARM.
First of all, the core itself is usually deeply embedded inside the device and is usually not directly visible within the scope of the device. The debug port is usually the only exposed part connected to the core itself, with some glue logic, such as clock and reset. integrated circuit.

Since the ARM core has only two interrupt inputs, the most common peripheral is some kind of interrupt controller. Inside the peripheral, each component is connected to each other through the on-chip interconnect bus architecture. For most ARM-based devices As far as I'm concerned, this is a standard AMBA interconnection.

AMBA specifies two buses, the high-performance system bus called AXI, and the low-power peripheral bus called APB, APB Usually used to connect all peripherals, AXI is used for memory and other high-speed devices. Most devices have a certain amount of on-chip storage and interfaces for connecting peripheral memory devices, but note that external connections to the device It is not the AMBA bus, this is only used inside the device and is not exposed.

4. Example: Exynos 4412 SCP

Let’s take Samsung’s Exynos (Orion) 4412 SCP as an example to explain these concept.

• Samsung’s Exynos 4412 SCP is a SOC based on Cortex-A9;

• As shown in the figure below, Exynos 4412 contains 4 Cortex-A9 processor (core);

• Cortex-A9 is based on the ARMv7-A architecture (instruction set)
  

As can be seen from the above picture, in addition to 4 Cortex-A9 cores, exynos 4412
also includes a large number of peripheral controllers: DRAM Controller, SROM Controller, Camera IF, JPEG, GPS/GLONASS, Power Management, USB Host, I2C, UART, SPI, etc.

Like Samsung, other major manufacturers that cooperate with ARM usually put their CPUs and various peripheral IPs together, and then take the drawings to tape out, and the products produced are also square. There are many pins below. This thing not only contains the CPU, but also other controllers. This thing is called SOC (system on chip).

As shown in the picture below, it is the Exynos 4412 finally produced by Samsung. Of course, this SOC alone cannot run Android, and a large number of peripherals are needed to finally form a complete system, but most The most complex hardware modules have been integrated into this SOC.

5. Summary

Let’s summarize these concepts:

• The name of the ARM company , called ARM: Advanced RISC Machines;

• The first microprocessor designed by ARM’s predecessor, Acorn Company, is called ARM: Acorn RISC Machine;

• ARM processor name: It used to be called ARM9 and ARM11. The new naming rules are changed to Cortex, which are Cortex-A, Cortex-R, and Cortex-M; the three letters A , R, and M together are ARM.

• ##ARM instruction set is the ARM architecture, such as ARMv8. Each processor needs to rely on a certain ARM architecture for design;

• **SOC: **Major manufacturers buy the ARM license, obtain the source code of the ARM processor, and then develop some IP for peripheral devices (either bought or designed by themselves) to form a SOC, such as Samsung Exynos 4412, Huawei's Kirin 990.

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