SiFive Announces U8-Series 2.6GHz High-Performance Out-of-Order RISC-V Core IP

SiFive claims a 3.1x uplift over the last-generation U7-Series, while beating Arm's Cortex-A72 on power and area efficiency metrics.

Gareth Halfacree
2 years ago

RISC-V pioneer SiFive has announced the launch of its U8-Series, core intellectual property (IP) aimed at high-performance devices — and claims it has Arm's rival Cortex-A72 beaten on efficiency and footprint.

Following on from the launch of the SiFive Shield security platform earlier this week, SiFive has unveiled a new core family it has dubbed the U8-Series. While the company's original focus was on low-power microcontroller-style cores, the U8-Series builds on the company's previous U7-Series — used to power the Linux-compatible HiFive Unleashed single-board computer — with a new out-of-order high-performance pipeline.

The results, according to SiFive's internal testing, are impressive: the SiFive U84, the company's mainstream U8-Series variant, is claimed to offer a 3.1x improvement in performance compared to the last-generation U74. Of that uplift, 2.3x comes from an increase in instructions per cycle (IPC); a further 1.4x comes from a higher maximum operating frequency of 2.6GHz. Going a few generations back, to the U54, the difference is even more stark: built on the same 27nm process, the U84 is an impressive 5.3x faster; moving to the 7nm process ups that to 7.2x.

SiFive isn't just positioning the U8-Series against its own products, though: the company is looking to take the fight to Cambridge-based Arm with a comparison to the company's popular Cortex-A72 core IP. Here, SiFive claims, the U84 offers twice the area efficiency and 1.5x better performance per watt - cramming a quad-core implementation with 2MB of L2 cache into just 2.63mm² — or 0.28mm² without the cache.

The company is also pushing the part as being inherently configurable. The core comes as standard with 12-stage out-of-order pipeline and triple issue queue; these can be configured as required for a particular workload, or custom instructions added to accelerate a given task — while also offering the ability to communicate with third-party accelerator IP. The U8-Series is also compatible with SiFive's Mix+Match, similar in concept to Arm's rival big.LITTLE, allowing for multiple core types and generations to be mixed in a single heterogeneous "core complex."

The U8-Series launches in two key variants: the mainstream SiFive U84 and the SiFive U87, which adds vector processing capabilities - full details of which the company has yet to unveil.

More information is available on the SiFive blog.

Gareth Halfacree
Freelance journalist, technical author, hacker, tinkerer, erstwhile sysadmin. For hire:
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