Fans have asked me what ARM is and how concepts like Cortex, ARM cores, ARM architecture, ARM instruction sets, and SoC are related. Below, I will clarify some concepts related to ARM.

1. ARM can be seen as a company name, a general term for a type of microprocessor, or a technology name. 2. ARM is a company specializing in the design and development of chips based on RISC technology. As an intellectual property supplier, it does not directly engage in chip production but transfers design licenses for partners to produce unique chips. 3. The ARM processor core is unified and provided by ARM, while the internal components are diverse and designed by various semiconductor companies, giving ARM a significant advantage in designing embedded systems using the same core with different internal peripherals.

Now, let’s introduce these concepts one by one.

ARM Company

ARM is primarily a company, short for Advanced RISC Machines. However, it did not originally have this name; let’s look at the growth history of ARM.

In 1978, an Austrian physicist named Hermann Hauser and his friend, a British engineer named Chris Curry, founded a company called “CPU”. The full name of this CPU company is Cambridge Processor Unit, literally meaning “Cambridge Processor Unit”.

After its establishment, CPU focused on the design and manufacturing of electronic devices. Their first order was to manufacture a microcontroller system for a gambling machine.

This microcontroller system was developed and named Acorn System 1.

It was called Acorn because they wanted to be listed before Apple in the phone book.

After Acorn System 1, they successively developed Systems 2, 3, 4, and a consumer box computer—Acorn Atom.

By 1981, the company had a rare opportunity—BBC intended to broadcast a series of programs across the UK to promote computer literacy, hoping Acorn could produce a computer to accompany it.

However, they found that their product’s hardware design could not meet the requirements. At that time, the trend in central processing units was shifting from 8-bit to 16-bit. Acorn did not have suitable chips.

So, they sought to approach the then-popular Intel, hoping to obtain design materials and samples of the 80286 processor. However, Intel ruthlessly rejected them.

Feeling demoralized, Acorn decided to create their own chips (how familiar this plot sounds!).

Thus, Acorn’s R&D personnel found a study on a new type of processor from the University of California, Berkeley—simplified instruction set, which happened to meet their design requirements.

Based on this, after years of hard work, computer scientists Sophie Wilson and Steve Furber from Cambridge University finally completed the microprocessor design. The former was responsible for instruction set development, and the latter was responsible for chip design.

Acorn named this chip Acorn RISC Machine.

This is the origin of the three letters **”ARM”**.

After ARM1, Acorn successively launched several series, such as ARM2, ARM3.

In 1990, Acorn established a company called ARM to collaborate with Apple.

Note that here, ARM is the company name, not the chip name. The full spelling of this ARM is also different: Advanced RISC Machines.

The previous chip name: Acorn RISC Machine and the current company name: Advanced RISC Machines

In the 1990s, ARM’s 32-bit RISC (Reduced Instruction Set Computer) processors expanded internationally, leading the low-power, low-cost, and high-functionality embedded system applications.

ARM does not produce or sell chips; it only sells chip technology licenses.

This policy allowed ARM to free itself from cash flow troubles and fully commit to chip research and development.

On April 17, 1998, the rapidly growing ARM Holdings went public on both the London Stock Exchange and NASDAQ.

In 2007, the groundbreaking product—the iPhone was launched. The first generation iPhone used ARM-designed chips manufactured by Samsung.

In 2008, Google launched the Android system, also based on the ARM instruction set. Since then, smartphones entered a rapid development phase, and ARM established its dominance in the smartphone market.

On July 18, 2016, it was reported that Japan’s SoftBank acquired the British chip design company ARM for £23.4 billion (approximately $31 billion).

On September 14, 2020, Nvidia officially announced it would acquire ARM from SoftBank for $40 billion. According to the agreement, Nvidia would pay SoftBank $21.5 billion in Nvidia stock and $12 billion in cash.

Currently, this acquisition has faced opposition from several Silicon Valley tech giants, including Intel, Qualcomm, and Tesla, who believe this deal would be detrimental to the industry. Additionally, regulatory bodies in China and the EU may oppose this acquisition.

Let’s wait and see!

ARM Cores and Architecture

Every ARM chip consists of two main parts: ARM core and peripherals.

ARM Core

ARM Core: includes a set of registers, instruction sets, bus, memory mapping rules, interrupt logic, and debugging components. The core is designed by ARM and licensed for use by chip manufacturers (ARM does not produce chips). For example, Cortex A8 and A9 are designed for high speed and are based on the ARMv7a architecture; Cortex M3 and M4 are based on the ARMv7m architecture; the former is the processor (the core), while the latter is the instruction set architecture (also referred to as architecture).

The peripheral part includes timers, A/D converters, memory, i2c, UART, SPI, ROM, etc., and is completely designed by each chip manufacturer to interface with the ARM core. Different chip manufacturers will have different peripherals, thus forming a vast ARM chip industry with numerous specifications.

ARM Instruction Set Architecture

The design of the instruction set is one of the most important parts of processor architecture, referred to in ARM terminology as ISA (Instruction Set Architecture).

The instruction set can be considered the soul of CPU design, the spell to unlock the Pandora’s box of CPU; to use the CPU, we can only operate it through these instructions.

For 32-bit CPUs, these instructions are sequences of 32-bit 01s, where different values represent different machine instructions. The hardware of the CPU can perfectly parse and execute these instructions, such as addressing, computation, exception handling, etc.

When we play games on our phones, we should know that every move we make is ultimately translated into a series of machine instructions.

Since the birth of the ARMv1 architecture in 1985, by 2011, the ARM architecture had developed to the eighth generation, ARMv8.

Cortex-A32/35/53/57/72/73/77/78 all adopt the ARMv8 architecture, which is the first ARM processor architecture to support a 64-bit instruction set.

Processor and Instruction Set Architecture Before ARM11

Before the ARM11 chip, the architecture relationship for each chip was as follows:

Processor and Instruction Set Architecture After ARM11

After the ARM11 chip, starting from the ARMv7 architecture, the naming convention for ARM changed.

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

Coincidentally, these three letters A, R, M are the same as ARM.

Cortex-A Series (A: Application)

This series is designed for the growing consumer entertainment and wireless products, used in applications that require high computing power, run rich operating systems, and provide interactive media and graphics experiences, such as smartphones, tablets, automotive entertainment systems, digital TVs, smart notebooks, e-readers, home networks, home gateways, and various other products.

Cortex-R Series (R: Real-time)

This series targets systems that need to operate in real-time applications, focusing on deep embedded real-time applications such as automotive braking systems, power transmission solutions, and large-capacity storage controllers.

Cortex-M Series (M: Microcontroller)

This series targets the microcontroller field, mainly for cost and power-sensitive applications such as smart measurement, human-machine interface devices, automotive and industrial control systems, household appliances, consumer products, and medical devices.

Cortex-SC Series (SC: SecurCore)

In addition to the three major series mentioned above, there is also a security-focused Cortex-SC series (SC: SecurCore), which is mainly used for government security chips.

The ARM11 series includes ARM11MPCore processors, ARM1176 processors, ARM1156 processors, and ARM1136 processors, all based on the ARMv6 architecture.

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

Cortex-A53 and Cortex-A57 processors belong to the Cortex-A50 series, which first adopted the 64-bit ARMv8 architecture.

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

What is SoC?

SoC stands for System-on-a-Chip, which means “integrating the entire system onto a single chip”.

SoC integrates many critical components found in smartphones, such as CPU, GPU, and memory. Thus, while it exists as a chip on the motherboard, it is composed of many packaged components.

For example, the Qualcomm 801, Kirin 950, Samsung’s Exynos 4412, A6, etc., are just the collective name for the packaged components (SoC). However, the packaging contents vary among different manufacturers for different reasons.

Classic ARM system-level chips, or SoCs, contain many components, some of which originate directly from ARM. First, the core itself is usually deeply embedded within the device and is typically not directly visible; the debug port is usually the only exposed part connected to the core, along with some glue logic, such as clock and reset integrated circuits.

Since the ARM core only has two interrupt inputs, the most common peripheral is some form of interrupt controller. Within the peripherals, various components are connected through an on-chip interconnect bus architecture. For the vast majority of ARM-based devices, this is the standard AMBA interconnect.

AMBA specifies two buses: the high-performance system bus called AXI and the low-power peripheral bus called APB. APB is usually used to connect all peripherals, while AXI is used for memory and other high-speed devices. Most devices have a certain amount of on-chip memory and interfaces to connect peripheral memory devices, but note that the connection to the outside of the device is not the AMBA bus; it is only used internally within the device and is not exposed.

Example: Exynos 4412 SCP

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

1. Samsung’s Exynos 4412 SCP is an SoC based on Cortex-A9;
2. As shown in the figure below, Exynos 4412 contains four Cortex-A9 processors (cores);
3. Cortex-A9 is based on the ARMv7-A architecture (instruction set).

As can be seen from the figure above, the Exynos 4412 includes four Cortex-A9 cores and a large number of peripheral controllers: DRAM Controller, SROM Controller, Camera IF, JPEG, GPS/GLONASS, Power Management, USB Host, I2C, UART, SPI, etc.

Similar to Samsung, other major manufacturers cooperating with ARM usually package their CPUs and various peripheral IPs together, and then take the drawings to produce a square chip with many pins. This chip not only contains the CPU but also various controllers, which is called SoC (system on chip).

As shown in the figure below, this is the Exynos 4412 produced by Samsung. Of course, having this SoC alone is not enough to run Android; it requires many peripheral devices to form a complete system. However, most of the complex hardware module components have already been integrated into this SoC.Currently, what major manufacturers do is purchase ARM licenses to obtain the source code for ARM processors, and then create some peripheral IP (either by purchasing or designing) to form an SoC before production. Different SoCs have different architectures (i.e., how the CPU connects to the IP; some are bus-centric, while others are DDR-centric).

HiSilicon has its own proprietary SoC architecture. However, regardless of how any manufacturer operates, they do not alter the CPU; the ARM core remains intact as the central processor.

ARM Licensing

How to understand ARM licensing?

For example, when we manufacture cars, ARM is like a company that owns the most advanced ‘engine’ design scheme but does not ‘produce engines’; instead, it licenses the design to major ‘automakers’ to produce, earning money to continue developing more advanced ‘engines’.

ARM licensing is divided into ARM architecture licensing, IP core licensing, and usage level licensing.

If a company wants to use ARM’s core to make its own processor, such as ST, Apple, Samsung, TI, Qualcomm, Huawei, etc., it must purchase different levels of licenses under ARM’s architecture based on its needs.

There are three types of architecture licensing: architecture level licensing, core level licensing (IP core licensing), and usage level licensing.

1. Architecture level licensing allows for significant modifications to the ARM architecture, even extending or reducing the ARM instruction set. Apple is a good example, having expanded its Apple Swift architecture based on the ARMv7-A architecture;

2. Core level licensing allows for the addition of peripherals to a core to form its own MCU, with many companies like Samsung and TI doing this;

3. Usage level licensing is the most basic requirement to use a processor; it means you can only use the defined IP provided by others in your design, cannot modify their IP, nor can you create your own encapsulated product based on their IP.

Therefore, if Huawei obtains both architecture licensing and IP core licensing, it means they can create their own core architecture based on the ARM instruction set and add various internal and external peripherals, such as communication interfaces, display control interfaces, GPIO, etc., to produce their own “processor chip”.

It’s similar to me writing an article and telling party A that they can modify it for use, which is architecture level licensing; telling party B that they can reference my article in theirs is core level licensing; and telling party C that they can only forward my article without changes is usage level licensing.

Conclusion

Let’s summarize these concepts:

1. The name of the ARM company is ARM: Advanced RISC Machines;
2. The first microprocessor designed by Acorn, the predecessor of ARM, was called ARM: Acorn RISC Machine;
3. The names of ARM processors: previously called ARM9, ARM11, the new naming convention is Cortex, which includes Cortex-A, Cortex-R, Cortex-M; these three letters A, R, M combine to form ARM.
4. The ARM instruction set refers to the ARM architecture, such as ARMv8, which every processor needs to rely on a certain ARM architecture for design;
5. SoC: Major manufacturers purchase ARM licenses to obtain the source code for ARM processors, then create peripheral IP (either by purchasing or designing) to form an SoC, such as Samsung’s Exynos 4412 and Huawei’s Kirin 990.