SiFive Announces Their Highest Power Core Yet

Brian Benchoff
Nov 4 · 3 min read

SiFive, the arguable leaders behind producing silicon based on the RISC-V open instruction set, have announced their highest performance core yet. The SiFive U8 series is a core built with the same technology as high performance server chips, and it has the processing power required for neural nets and deep learning. In effect, this is the chip fans of Open architecture have been waiting for.

The SiFive HiFive Unleashed

SiFive have made a name for themselves in the last few years for capitalizing on the RISC-V instruction Set Architecture, a completely Open specification for CPUs originally created at Berkeley. Unlike ARM, Intel, and nearly every other CPU architecture, RISC-V is Big-O Open and unencumbered with licensing and patents. This is a remarkable change from the previous half century of CPU design, and so unique we really aren’t sure of the implications quite yet.

To date, SiFive have released several cores, mostly focusing on smaller microprocessor-sized chips. The SiFive E20 and E21 are similar to an ARM Cortex-M0+ and Cortex-M4, while the HiFive Unleashed is capable of running Linux about as well as a Raspberry Pi. These are just basic comparisons, but you get the idea.

A New Microarchitecture

With the success of their current cores, SiFive has turned to significantly more powerful and scalable technology for their next chip. This means technology that was first pioneered back in the Mid-90s, yes, but SiFive’s latest core, the U8 series, will include Out-of-Order execution.

This means more complex workloads and higher performance, much more than what the microcontroller-like SiFive cores are capable of now. The anticipated performance of the U8-series chips will have 1.5 times the performance per Watt, and double the area efficiency of previous cores.

In terms of performance gains, the SiFive U84 will see up to seven times the performance of the earlier SiFive U54 chip.

But these are architectural advancements. SiFive has invested heavily in this IP, and this new chip will also include process advancements. Where the earlier U54 cores were fabricated at a 28nm node, the U84 chip is able to be fabricated at a 7nm process node, most likely with TSMC’s processes.

Add these things together, and SiFive just announced a modern CPU capable of doing everything you would expect. It’s also completely Open.

What Will A RISC-V Desktop Look Like?

SiFive’s U8-series chip will be a powerhouse, at least on par with a run-of-the-mill laptop, and perhaps approaching the capabilities of a modern desktop. If you want anything more, you’ll also be looking at a graphics card. While other Open CPUs have this sort of processing power — namely the Raptor Talon desktop with a POWER9 CPU, the SiFive U8 may be a little bit less expensive.

But what is this RISC-V desktop going to be like? For that, we can turn to a desktop made out of an earlier RISC-V development board. That’s what Andrew Black did with the HiFive Unleashed:

This ‘desktop’ RISC-V is actually just a few development boards cobbled together into a complete working computer. Still, for a truly Open architecture, everything just worked. It runs Linux, and you can do actual work on it. No, it’s not as capable as a modern desktop computer, but it’s something.

When SiFive’s U8 CPU finally hits development, we can expect to see similar efforts to build a Big-O Open desktop, but the real story here is the ability for any manufacturer to use what SiFive has produced to build their own hardware.

The future of RISC-V isn’t in custom-built desktops, it’s in manufacturers using the chip in set-top boxes, or in small, custom hardware. Western Digital is already looking at RISC-V for their drive and server products, and RISC-V might soon be making it into the datacenter. With that, we’ve got a future for RISC-V, and Open processors in general.

Brian Benchoff

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Discussing the business of hardware and hardware manufacturing.

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