China Developing its Own CPU Instruction Set Architecture

23-04-2021 | By Sam Brown

China has been looking to become self-sufficient in the semiconductor industry, and has recently announced its own Instruction Set Architecture. What is an ISA, why does China want to be self-sufficient, and what do we currently know about the new ISA?

What is an ISA?

An Instruction Set Architecture, or ISA, describes the registers, instruction, and memory model of a CPU. Still, it does not describe the physical implementation (i.e. how the chip implements the instructions). Two processors can be constructed in a fundamentally different way (such as Intel and AMD). Still, if both use the same ISA then they will be able to execute code identically.

Even though ISA is more of a concept than anything physical, it is still intellectual property, and when designing a CPU it is important to take this into account. For example, the x86 architecture was developed by Intel, and they have licensing rights to this. RISC-V, however, is open-source and anyone creating a CPU from scratch can happily use this instruction set.

Why is China moving towards semiconductor self-sufficiency?

Most semiconductors are manufactured in the east (Taiwan, South Korea, and China), and China is responsible for a very large portion. However, while China may be responsible for manufacturing op-amps, transistors, and diodes, they do not manufacture many western high-end processors (if at all). Instead, China relies on importing such devices, and this puts China at a major disadvantage.

There is no real reason for China not being able to manufacture such parts. They have the semiconductor facilities to fabricate such chips, and certainly have the funds to do so. The two most popular instruction sets in the world, x86 and ARM, are proprietary, and most operating systems use these ISAs. If China attempted to manufacture CPUs with such ISAs they would be found out almost immediately, and the resulting backlash from other nations would include trade embargoes and sanctions. 

China could utilise open-source architectures such as RISC-V which do not require any licensing or special permission. However, RISC-V is a western development, and using RISC-V would put China at the mercy of the developers of RISC-V who may make changes to the architecture that China either doesn’t need or doesn’t want. 

Loongson Announces Development of New ISA

Recognising the need for an in-house solution that would allow China to steer its own ship, Loongson has recently announced the development of a new ISA. The new ISA, called LoongArch, has been said to be entirely independent from X86, ARM, and RISC-V in its entirety which means that it will not violate any patents or existing intellectual property.

According to Loongson, the development of a new ISA allows them to develop CPUs without needing authorisation from western companies and allows them to develop their own independent industrial ecosystem. Furthermore, China developing its own ISA also allows it to license the CPU architecture to other Chinese developers, quickening development time for new hardware and software.

Currently, the architecture documents have only been released to a handful of individuals, but what is known is that the instruction set includes 2500 instructions with vector instruction, virtualisation, and binary translation. Furthermore, Loongson announced that its first LoongArch processor, the LS3C5000 will integrate 16-cores, have a clock frequency of 2.5GHz, manufactured using a 12nm process, and will aim to match the performance of Intel and AMD server processors.

While the development of LoonArch does move developmental powers back to China, it does come with some major drawbacks. The first challenge is developing software tools for the new architecture as a new ISA will have no tools at all. 

Secondly, if the ISA is proprietary, it may be difficult to compete with other ISAs such as RISC-V, which are free and have a supportive community and free online software resources. 

The third major challenge is that the new ISA will not support any operating systems currently in widespread use such as Window and Linux.

The four major challenge is that the development of a new ISA means that the ISA and the resulting processors will not have been proven like x86 and ARM who each have many decades of improvements and adjustments. As such, safety-critical applications may not be able to reliably use the LoongArch ISA until it has proven itself for several years.

It would seem that China is moving towards a custom architecture for the sake of having something that is “non-western”, and in the long run will most likely be a poor decision. If China is serious about creating its own processors, RISC-V would be a far better choice for software and hardware compatibility.

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By Sam Brown