RISC-V: The Next Gen CPU Architecture

Semiconductors products like CPU & GPU are the heart & soul of any Modern-Day Machines. In smartphones, ARM licenses its products to other companies like Qualcomm, Samsung, Apple & Mediatek which then develop their own custom System On Chips (Also called SoCs. A SoC is an integrated circuit that will have CPU, GPU, Modem, I/O Ports, Memory & etc on a single microchip).

On the other hand, all the modern Laptops/Computers run on Central Processing Units (CPUs) which are x86-64 (or amd64/x64) architecture based. These CPUs are exclusively designed and developed by two companies, namely AMD & Intel. These CPU then sits on motherboard manufactured by some other companies. These motherboards will then in turn have their own designs & support for different hardware (like GPU, Sound Card, Lan Ports & etc).

The ARM model is now also penetrating in the Laptop/PC space, as last year Apple started pushing it’s own in-house developed ARM based SOCs to its Mac line-up following the Steps of Microsoft which has been porting Windows 10 to ARM for a while.

RISC vs CISC: The long-lasting battle:

Before delving onto RISC-V, lets us first understand what do we even mean by RISC.

Above, I have used ARM. So, ARM based chips are family of chips that use Reduced Instruction Set Computer (RISC) Instruction Set Architecture (ISA). While earlier iterations of x86-64 were Complex Instruction Set Computer (CISC) based but the modern-day iterations of x86-64 does have included bits of RISC too making it somewhat a hybrid.

RISC is built to minimize the instruction execution time by optimizing and limiting the number of instructions. It means each instruction cycle requires only one clock cycle. On other hand, CISC approach is to reducing the number of instructions on each program and ignoring the number of cycles per instruction. Therefore, a program might need less step on CISC than RISC as often a single Complex instruction on CISC will equal to performing multiple instruction on RISC.

We might think that 2nd seems a better approach & might give better performance, but that’s not how it plays as each system requires exactly the same time to execute a program. This is mainly due to the fact that CISC will take as many clock cycles as RISC approach. Therefore, RISC based chips are also much more power efficient than their CISC counterparts, allowing for longer battery life on Mobile/IoT based products, thus making them more useful & viable.

What is RISC -V then?

Reduced Instruction Set Computer – V or RISC-V is a free and open ISA which enables a new era of processor innovation through open standard collaboration. The project began in 2010 at the University of California, Berkeley along with many volunteer contributors. RISC-V is established on reduced instruction set computer (RISC) principles thus leveraging it’s overall benefits.

The goal was to make a practical ISA that was open-sourced, usable academically and in any hardware or software design. The RISC-V ISA is thus provided under open-source licenses, allowing it to be used without royalties unlike ARM’s licensing. RISC-V has a modular design, consisting of alternative base parts, with added optional extensions. Therefore, RISC-V combines a modular technical approach with an open license business model, meaning that anyone, anywhere can leverage the IP contributed and produced by RISC-V International to build products.

Semiconductor Industry is very hard to penetrate industry for any company due to enormous cost of development (Think Billions of Dollars) & production that is involved upfront. RISC-V was able to break down many barriers in the semiconductor industry, bringing together different companies, industries, and geographies for open collaboration.

The Indian Outlook:

Semiconductor is the one of the key components that is very essential to build the infrastructure for modern, secure, self-reliant digital India. India has significantly lagged in semiconductor technology whereas many of its neighbouring Asian countries were able to keep up with development like China, Taiwan, Korea, Japan & etc.

India currently has no consumer foundries yet and thus Indian government is once again trying to get a fabrication plant setup in India. Recently, the Indian government has announced that $1 Billion+ will be made available in Cash to Chip-maker companies that sets up manufacturing units in the India as part of its “Make in India” Initiative. The government is hoping to build on its ever-growing smartphone assembly industry to strengthen its electronics supply chain. The locally manufactured chips will further bring down the cost of a Smartphone & IoT based products and reduce imports. The chips that will be made locally will also be designated as “trusted sources” and will be used in products ranging from CCTV cameras to 5G equipment in future. It should finally help India Gain a foothold in Semiconductor Industry as the growing demand for electronic Smart Devices has only exploded since COVID-19 era.

In 2020, the government also announced a national competition to foster the use of the nation’s homegrown RISC-V microprocessor designs in the hope the tech will eventually replace imported parts, and be used to create products in demand around the world.

Credits: Openhwgroup’s CVA6 – 6-stage, single issue, in-order CPU on RISC-V ISA

Shakti Processors – IIT M:

The SHAKTI Processor Program, was started as an academic initiative back in 2014 by the Reconfigurable Intelligent Systems Engineering (RISE) group at IIT-Madras. It is completely Open-source Project like RISC-V. The major aim of the Project is to bridge the gap between academia and industry, to provide innovative and customized solutions without the hassles of royalties!

The SHAKTI project is currently building a family of 6 processors, based on the RISC-V ISA. The project has currently developed an Embedded class (called E-Class) and Controller class (called C-Class) of processor based on the RISC-V ISA. Shakti have been taped out and fabricated at 180nm by the Indian government’s Semi-conductor Laboratory in Chandigarh (A 200mm fab owned by ISRO), and at 22nm by Intel’s foundry with FinFET+ technology. Last Year, Indian defence and strategic sector also started using the Risecreek processor (64-bit RISC-V based, clocked at 100-350 MHz) developed by IIT-M and fabricated by Intel.

C-DAC’s VEGA:

Centre for Development of Advanced Computing (C-DAC) is also developing VEGA Processor. These Processors are also based on RISC-V ISA. VEGA is a series of 32-bit/64-bit Single/Multi-core Superscalar In-order/Out-of-Order high performance processors integrated with Multi-level Caches, MMU and Coherent Interconnect.

Future Prospects:

Linux Kernel & its related tools have already implemented support required to bootup RISC-V based processor. RISC-V based CPUs are also already deployed in some data centres & many other areas of Server Infrastructure. Since, development cycle for processors are generally long (3-4 years at minimum), we should expect a lot more variety as more companies start releasing their own works in future.

In mobile especially, replacing ARM will be a challenge that cannot be achieved in a year or two given its deep ties in both the Android & iOS ecosystem where apps & games are optimized on ARM’s architecture. Additionally, there is not much traction where RISC-V based SoCs are in development for such use case. This might change in due time as more companies wouldn’t want to continue paying for ARM’s licensing fees and build around RISC-V for long term benefits.

Many companies like Alibaba Group, SiFive, Western Digital & lot more institutes & organizations have already forayed into building and developing products based on it. Recently, Intel announced its plan to open its foundries to fabricate RISC-V & ARM chips as part of new business strategy. This could be very helpful in the long run as companies will have wider sources from where they could fabricate their chips.

Though may be not this decade but surely in the next coming decades, RISC-V will definitely standout as ISA for ALLL and will get more mainstreamed as the time & resources that are required to build semiconductors are invested. On a different note, we should also think that the vast potential of RISC-V will be definitely tapped into in this decade as general IoT based products could be available by mid or end of decade at latest. So do keep an eye out on those when they are available. As we also seen, RISC-V will also bring many benefits for India as whole as many Indian companies could build around it to build their next-gen smart products to avoid licensing fees for ARM & avoid making something from scratch-up.

(The article too was also written for the College Magazine. You can find the entire copy of the magazine here: https://www.tcetmumbai.in/COMP/E-magazine/NIMBUS%202021.pdf)