Arm has taken offline its website attacking rival processor architecture RISC-V within days of it going live – after its own staff objected to the underhand tactic.

The site – riscv-basics.com – was created at the end of June, and attempted to smear open-source RISC-V, listing five reasons why Arm cores are a better choice over its competitor's designs. However, the stunt backfired, with folks in the tech industry, and within the company's own ranks, slamming the site as a cheap shot and an attack on open source.

That last part in particular made Arm bosses U-turn: the Softbank-owned CPU design house, responsible for billions of CPU cores in smartphones, tablets, smart cards and other embedded kit, is heavily reliant on an ecosystem of open-source code and developers. Thus laying into the RISC-V movement looked like a declaration of war on open-source technology.

If anything, the site made RISC-V sound like a viable alternative to Arm's crown, giving the upstart architecture more credibility.

Arm is right to be rattled by RISC-V. Western Digital has thrown its weight behind the architecture, Nvidia is using it as the glue inside its future graphics cards, plus it is backed by Google, Samsung, Qualcomm, and other organizations – many of which are Arm licensees.

And being open source, RISC-V cores can be studied, improved, and validated by a large cooperative community, which is an exciting prospect.

Background

RISC-V is an open-source processor instruction set specification, overseen by the non-profit RISC-V Foundation, with freely available implementations – whereas you have to pay millions of dollars to Arm for the rights to use its CPU cores and architectures.

People who want to build their own system-on-chips can take royalty-free BSD-licensed RISC-V cores from GitHub, customize them, bolt on their own crypto or math acceleration, input-output support, and other peripherals, and pass the designs to chip factories to fabricate, which in theory works out a lot cheaper than using Arm's CPU cores.

Upstarts such as SiFive will help turn your RISC-V-based blueprints into physical chips, and outfits such as Greenwaves are using the technology to craft multi-core SoCs, with neural network acceleration, for drones and other embedded gear. SiFive also has its own system-on-chips available for you to get your hands on, LowRISC is working on its own open-source SoC, and you can run RISC-V cores on FPGAs or in emulators such as Qemu.

Sure, RISC-V is in its infancy, and its cores can't keep up with Arm's top-end Cortex-A offerings, for the moment at least. However, it is threatening to give Arm a run for its money in the microcontroller and lower-end, low-power world.

Both RISC-V and Arm's 64-bit Armv8 architectures share the same RISC roots going back the 1980s. RISC-V was born in Berkeley, California, in 2010, founded by Krste Asanović and colleagues with the help of computer science ace David Patterson, who coined the term RISC, cowrote essential textbooks on CPU design, and led early efforts to create RISC processors.

Just like on Arm, you can boot Linux and other ported operating systems on RISC-V cores – which come in 32-bit, 64-bit and 128-bit flavors – and use them as general-purpose or specialist processors. RISC-V and Armv8 both have a zero register, both have 31 or so general purpose registers, both shun multiple register loading and saving from and to memory, both support multiple levels of privilege, both do virtual memory and access protection, both look a little like 64-bit MIPS if you squint, and so on.

RISC-V and Arm both run software written in C, C++, Go, Rust, Python, and other languages. To programmers, the architectures appear quite similar.

The claims

Arm's five allegations against RISC-V centered on cost, ecosystem, fragmentation, security, and design assurance.

"Whether you are looking to create a chip from scratch or looking for a complete solution, take advantage of an architecture that has been tried and tested in more than 125 billion chips and already in processor designs licensed by more 500 partners," the site smugly put.

On the point of cost, Arm tried to argue that while RISC-V cores are free to use, you still have to design plumbing around them, and then get the things manufactured, none of which is cost free. Of course, anyone preparing to create a system-on-chip will know this – so El Reg can only assume this was an appeal to investors and shareholders that Arm wasn't about to be totally undercut by an open-source upstart.

Brains behind seL4 secure microkernel begin RISC-V chip port READ MORE

On the ecosystem, yes, Arm has a large one – but RISC-V is just starting, so it's a cheap shot. At one point, Arm was an internal project at Britain's answer to Apple – Acorn Computers – and it took several years to reach its level of dominance today.

On the fragmentation risk: Apple, Samsung, and Qualcomm have their own flavors of Arm-compatible cores out in the wild, while we've lost count of the times Arm has come up with different math unit extensions.

On security: Arm cores suffer from Spectre and Meltdown flaws, and TrustZone fell to crap firmware programming by Arm's customers. RISC-V cores avoided Spectre and Meltdown by not having the same level of speculative execution – and its designs are open for anyone to scrutinize and improve.

On design assurance: Arm claimed again it is expensive to validate designs, but anyone serious about building their own chips will know this, so again, it looks like an appeal to investors, analysts, and journalists.

Fear, uncertainty and doubt

In response to Arm's outburst, the inevitable arm-basics.com, piling into Arm's approach to licensing, emerged online, and infosec guru Maria "Azeria" Markstedter vowed to create arm-basics.de with guides on how to write exploits for vulnerabilities in Arm-powered systems.

"Arm’s negative campaign against RISC-V can only backfire," said GNOME and Xamarin cofounder Miguel de Icaza on Twitter. "Also, their points are kind of weak. This was attempted before against open source, and all it achieved was eggs on people’s faces."

Arm told us it had hoped its anti-RISC-V site would kickstart a discussion around architectures, rather than come off as a smear attack. In any case, on Tuesday, it took the site offline by killing its DNS.

“Our intention in creating a webpage to offer key considerations around commercial RISC-V based products was to inform a lively industry debate," an Arm spokesperson told The Register.

"Regretfully, the result was something different, a page that wasn’t in line with Arm’s collaborative culture, so we’ve taken it down. Indeed, many of our own people also told us they didn’t like it.

"One thing to clear up immediately is we absolutely did not want to give the impression we were attacking open source as we are highly committed supporters of open source communities in many different areas. Our intention is to cultivate a healthy discussion around architectural choices as it is one of many subjects critical to our industry’s future.”

A spokesperson for the RISC-V Foundation was not available to comment. ®