[cottonseed]

I'm not familiar with the IP issues. Would it be possible to center open-source processor development around the ARM instruction set?

It looks like the privileged part of the RISC-V ISA is not finished yet. This is a great project, but it seems a long way off.

[makomk]

I'm surprised they don't just use OpenRISC, there's already hardware shipping that uses ASIC implementations of that internally.

[mjn]

They discuss their reasoning briefly in the manual [1, p. 3]:

We are far from the first to contemplate an open ISA design suitable for hardware implementation. We also considered other existing open ISA designs, of which the closest to our goals was the OpenRISC architecture. We decided against adopting the OpenRISC ISA for several technical reasons:

-- OpenRISC has condition codes and branch delay slots, which complicate higher performance implementations.

-- OpenRISC uses a fixed 32-bit encoding and 16-bit immediates, which precludes a denser instruction encoding and limits space for later expansion of the ISA.

-- OpenRISC does not support the 2008 revision to the IEEE 754 floating-point standard.

-- The OpenRISC 64-bit design had not been completed when we began.

[1] http://www.eecs.berkeley.edu/Pubs/TechRpts/2014/EECS-2014-54...

[zanny]

Or SPARC, which is patent and license free, open, and has a decade of shipping in real hardware to back it up.

[wmf]

Historically, ARM really, really did not like unlicensed or open-source ARM processors. But times change, so I wouldn't be surprised to see them take some easy PR from openwashing at some point.

[higherpurpose]

That seems highly unlikely - unless we're talking about 3rd generation behind the latest tech chips. I could see them open source say the ARMv6 architecture in 3+ years, when ARMv8 has already taken off, and ARMv7 is in legacy mode. But meh.

[sitkack]

ARM would very aggressively go after any open source implementation of the ARM ISA. For the longest time you couldn't find any ARM documentation on the net because it was all behind a license agreement that read, "won't be used to make an open source version of our schwag"

[userbinator]

If I remember correctly, the last time I checked 586-level x86 was fully open and some of the P6 patents were close to expiring, so it might make another contender for an open-source CPU. Since Intel and AMD don't license x86 soft-cores unlike ARM and MIPS (which RISC-V is similar to), I think there could be fewer legal issues. Compatibility is another bonus; it's possible to put an entire PC-compatible on a single chip: http://www.vortex86.com/dx