Custom CPUs - The RISC-V Revolution

From Bathtub Thoughts to Custom CPUs: The RISC-V Revolution

Introduction

Have you ever found yourself relaxing in the tub thinking, "How could I design my own CPU?" While that might not be a common thought for most of us, large companies genuinely face this question. The traditional approach would be licensing intellectual property from giants like Intel or ARM—but that costs an arm and a leg. So what alternatives exist?

When this question was posed to Krista Asanovich, co-creator of RISC-V, he brought over a team of people and a computer based on RISC-V's free and open architecture that surprisingly functions like a normal PC.

Beyond the Tech Demo

You might be thinking, "Cool tech demo running Quake 2, but I won't have one of these open processors in my computer anytime soon, so why should I care?"

Here's why: You can expect to find RISC-V processors in your gaming rig much sooner than you'd think—just not yet as your primary CPU. Companies like NVIDIA, Western Digital, and approximately 100 others will soon ship products with RISC-V microprocessors due to their:

- Better efficiency

- Improved security

- Royalty-free licensing

A Brief History Lesson

To appreciate RISC-V's innovation, we need to understand some computing history:

The 1960s: The Microcode Era

- RAM was made using tiny magnetic cores—extremely slow compared to vacuum tube processors

- To prevent wasting cycles, processors ran "microcode" (small hardwired programs) while waiting for memory

 The 1970s: The Space Race Effect

- Scientists figured out how to put many transistors on a single chip

- Fast memory could now be placed on the same chip as the CPU

- Contrary to what you might expect, microcode wasn't abandoned

The x86 Legacy

- Intel's 8086 CPU pioneered the x86 architecture

- It was hastily created in just weeks with no expectation of becoming the standard for decades

- Today, x86 has ballooned to over 1,500 instructions—adding roughly one instruction every couple weeks

- This bloat leads to inefficiency and creates barriers for new processor development

 Why We're Still Using x86

- Software support is crucial—porting Windows and its programs to new architectures has proven challenging (remember Windows RT on ARM?)

- Creating a good architecture from scratch is extraordinarily difficult

- For decades, it was easier to make transistors smaller rather than redesign the architecture

- Moore's Law has slowed, and CPU speed improvements have plateaued in recent years

 Enter RISC-V

With modern processors needing a better alternative to x86 and ARM, Krista and his team created RISC-V (Reduced Instruction Set Computing 5):

- Core design has fewer than 50 instructions (versus x86's 1,500+)

- These core instructions are locked down and won't change, ensuring future compatibility

- Beyond the core, RISC-V is customizable—companies can add specialized instructions for specific tasks

- This allows for greater hardware specialization and efficiency

Why This Open Source Instruction Set Matters

Previous open-source instruction sets failed to gain traction, so why is RISC-V different? The RISC-V Foundation's membership reads like a who's who of tech giants:

- Google

- Samsung

- NVIDIA

- Tesla

- IBM

- 100+ more companies

Additionally, a startup called SiFive (founded by RISC-V's creators) is helping kickstart adoption by creating the first commercial RISC-V silicon.

 The FU540 Processor

The FU540 ("Freedom Unleashed 540") processor showcases RISC-V's potential:

- $1,000 processor with four cores clocking up to 1.6GHz on a 28nm process

- Not breaking speed records, but that's not the point

- When announced with Linux support, almost nothing ran on it

- Just six months later, 80% of the Debian software library had been compiled for RISC-V

The demonstration board features:

- The processor under a small heatsink and fan

- 8GB of DDR4 RAM with ECC

- Gigabit Ethernet

- USB ports

- Micro SD card reader

What makes it unique is the ChipLink connector, allowing the CPU to connect to virtually anything. The demo showed a unit connected to an FPGA handling PCIe lanes, effectively creating a larger-scale motherboard with:

- A standard AMD HD 6450 graphics card

- Samsung M.2 drive

- Expanded I/O options

 The SiFive Approach

SiFive is taking a "Domino's Pizza approach" to custom chips:

- Companies can add specialized components for image processing, AI, etc.

- The open-source nature allows companies to fix driver issues themselves rather than waiting for vendor support

- If SiFive were to disappear, development investments wouldn't be wasted

 Education: The Real Driver of Adoption

The royalty-free nature of RISC-V has made it the architecture of choice in education:

- The most popular computer architecture textbooks and courses now use RISC-V

- Previously, students learned on "fantasy architectures" before transitioning to messy proprietary systems in the workplace

- Since few engineers switch architectures after entering the field, this educational foundation will drive future RISC-V adoption

 The Future of RISC-V

Expect to see RISC-V processors appearing in:

- Hard drives

- Graphics cards  

- Automobiles

- And potentially, someday, as the primary architecture in your home computer—running games far more complex than Quake 2

Conclusion

RISC-V represents a fundamental shift in processor design philosophy—from closed, proprietary, and increasingly complex architectures to an open, streamlined, and customizable approach. While it may not replace your main CPU immediately, its influence is already spreading throughout the technology ecosystem, promising a more efficient and innovative computing future.