RISC-V Cores Get Support, Fees

Instruction sets may want to be free, but cores--maybe not so much. Startup SiFive announced a new embedded RISC-V core and a relatively simple way to access its processor cores on its Web site, however, they come with one-time licensing costs in the mid-six figures.

SiFive made its existing 32-bit E31 core and a new 64-bit E51 version available for one-time fees of about $300,000 and $600,000, respectively. An open source core called Rocket created by some of SiFive's founders remains available for free online. It can be used to configure and generate 32- and 64-bit processor cores.

The SiFive news comes just before the sixth workshop of the RISC-V open instruction set group, its first in China.

SiFive will have to compete with a wide range of cores from Cadence, Cortus, Imagination, Synopsys and Andes--which rolls out its first 64-but core next week. The existing players have more mature ecosystems and cores that also sell for less than a million dollars, said Linley Gwennap, principal of the Linley Group (Mountain View, Calif.).

“I thought their original business model was the core would be open source, so they seem to have changed their business model…They are trying to innovate but at the end of the day everyone has costs,” Gwennap said.

“A year ago there was quite a debate if people would license a core if there was a free version, [but now] we’ve seen significant demand for customers who don’t want an open-source version but one better documented with a company behind it,” said Jack Kang, vice president of product and business development at SiFive.

SiFive provides just the processor core, but researchers at Berkeley and elsewhere have released other elements such as the TileLink interface. (Image: SiFive)

The E31 and E51 come with a warranty the cores will hit a specified performance target as well as indemnification, documentation, test benches, constraint files and integration files. “The analogy here is with Red Hat that provides a package with support,” said Kang.

SiFive points to the value of making its silicon IP easy to access and royalty-free. Royalties are not a big issue for engineers who typically forecast their lifetime needs for a core and figure that into a total negotiated price," said Gwennap.

Datasheets and other detailed information to evaluate the cores, including FPGA bitstream models and an evaluation version of functional, synthesizable RTL for the E31 are freely available on the company’s Web site. The site also lets engineers configure cores and buy them after agreeing to a seven-page licensing contract online.

“The ability to try, configure and buy a core over the Web is unheard of, and there’s no royalties so you don’t have to figure out how many you are going to sell,” said Kang.

“You can buy all sorts of software online and can even set up an Amazon data center service with a few clicks, so why is the silicon IP industry so far behind?” asked Kang. “We have to get IP from others and it’s incredible how hard it is, so we have a chance to do something new for the industry,” he said.

Both the E31 and E51 can run at data rates up to 1.4 GHz in a 28 nm process. The E31 is roughly comparable to an ARM Cortex M3 or M4. The E51 creates a new entry-level for an embedded 64-bit core below ARM’s Cortex A53.

Neither core runs Linux, SiFive plans to roll out a separate U54 core for standalone processors running Linux later this year. It may roll out an additional E-series cores before the end of the year.

FreeRTOS, Project Zephyr and Apache Minute OSes have been ported to the current E31 core. The RISC-V architecture now has available a GCC compiler for C, a GNU debugger and other peripheral tools. SiFive provides an SDK and an Eclipse-based development environment.

“There’s been huge progress in the RISC-V ecosystem,” said Kang.