We're closing the gap with Arm and x86, claims SiFive: New RISC-V CPU core for PCs, servers, mobile incoming

As it appears Intel's attempt to gobble the upstart collapses


SiFive reckons its fastest RISC-V processor core yet is closing the gap on being a mainstream computing alternative to x86 and Arm.

The yet-unnamed high-performance design is within reach of Intel's Rocket Lake family, introduced in March, and Arm's Cortex-A78 design, announced last year, in terms of single-core performance, James Prior, senior director of product marketing and communications at SiFive, told The Register.

San Francisco-based SiFive didn't provide specific comparative benchmarks, so you'll have to take their word for it, if you so choose.

RISC-V is an open-source, royalty-free instruction set architecture for CPU cores: RISC-V International sets the specifications, and semiconductor designers like SiFive implement them as designs that can be slotted into system-on-chips for customers among other IP.

SiFive's latest design, which is set to be teased today, will be christened with a formal name at the RISC-V Summit in December.

The CPU core is said to be about 50 per cent faster than its predecessor, the P550, which was introduced in June. We note that the L3 cache memory capacity has been quadrupled, from the 4MB in the P550 to 16MB in the new design. Up to 16 of these new cores can be clustered versus the maximum of four for the P550. The latest design can also run up to 3.5GHz compared to 2.4GHz for the P550.

The new CPUs can go in PCs and servers, and be scaled down for mobile and embedded devices, Prior said.

It's been an action-packed week for RISC-V. Intel, which is already testing and evaluating the P550 chip design, was said to be in talks to acquire SiFive, though Bloomberg reported today those negotiations fell through. SiFive declined The Register's request for comment on that, calling the reports of a proposed takeover "media speculation."

Alibaba also open-sourced a bunch of RISC-V CPU designs under an Apache license.

SiFive's new CPU core otherwise doesn't have much of an architectural difference from the P550, Prior said. The core design is a superscalar out-of-order 64-bit affair that supports the usual things like double-precision floating point. The chip retains a modular design to which additional acceleration units like vector processors or GPUs can be attached within a system-on-chip.

The processor blueprints also have the hooks onto which interfaces for DDR5 RAM and PCI-Express 5.0, which are supported by the latest Intel Alder Lake chips, can be added. But that will depend on whether a customer wants to include those features in their custom system-on-chips, Prior said.

SiFive provides a web-based design tool so folks can tweak a RISC-V CPU core to their needs, and get the corresponding RTL data for evaluation on FPGAs. Customers can tack on accelerators for AI applications and other IP to eventually form a design for a system-on-chip ASIC for manufacture, if they so wish, in conjunction with SiFive. The new CPU core is set to be available from SiFive's online configure-it-yourself tool from next year.

"We'll offer an RTL deliverable in 2022, that you'll be able to run on FPGA models, begin prototype software development, and modeling as you understand exactly how it works," Prior said.

Loads of companies now are looking to design, or have designed and deployed, their own customized chips to create a fully owned vertical stack, from the software at the top down to the hardware optimized for particular applications at the bottom. Apple transitioned from PowerPC and x86 to crafting Arm-compatible parts for laptops and desktops, and boasted how its homegrown M1 Pro and M1 Max Pro silicon can deliver high performance and longer battery life than Intel-compatible rivals.

SiFive has more than 100 customers, including some of the top technology companies in the world we're told, looking at its designs. Alibaba open-sourcing its own RISC-V cores in this space is good as it could generate a lot of interest, force the pace of development, and spur RISC-V innovation, Prior said.

But anyone can offer free cores, and with the trend to customizing processors for particular types of workload, there's more interest in what can be done with a chip to achieve that as well as providing support and software stacks around it, he continued.

"Having it tested and verified on silicon, and a tool chain to go with support, for people call up and say 'how did you do this?' – that is the inherent value of an IP company like SiFive," he said. ®


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