Right now, the "official" RISC-V reference implementation, Rocket, is still ASIC-optimized. FPGA-based RISC-V cores tend to be home-grown things these days.
You can still synthesize Rocket on an FPGA, but because it's optimized for ASICs, it needs a rather large FPGA to do so, since it's investing individual LUTs to things that can be only a few transistors in an ASIC.
To this day, my own KCP53000 core is *still* the only 64-bit FPGA-optimized core I'm aware of.
Both have their limitations, however; neither design can run Linux, for example.
I hope that my successor design (KCP53010 -- still vaporware!) will remedy some of them (it should be able to run Linux if it's ported), but it still won't be as complete or as fast as Rocket.
@vertigo What I mean is that the current state of affairs makes every industrially-made CPU suspectful. Especially those made in countries with governments known for spying on citizens wholesale, who attempted to build the Clipper chip in the past.
I'm wondering how far we can go building these systems really from scratch. We still depend on Xilinx or Altera/Intel at some point anyway.
I'm curious about your point of view on these matters.
@bob @jjg @cstanhope @h Wasn't there someone looking to make 10um or 8um feature-sized semiconductors using garage-accessible equipment not long ago? If so, and once you're familiar with the characteristics of the transistors at those sizes, you can definitely at least make a Z80 or 6502 equivalent CPU.
My motivation is threefold:
1. Learn how to actually build stuff with FPGA and start with open tools of at all possible
2. Design a module for RAIN that can be used to provide application-specific logic, acceleration and other experimental stuff along side the traditional processor modules
@jjg This is amazing news! Tangentialy related: I'm trying to see how hard it would be to build a REBOL interpreter in a common assembler (similar to the way Forths are often built). The main reason is I would like my work-in-progress hypermedia engine to eventually run on your free computer architecture and on @vertigo's as well.
@cstanhope I had expected to write a Lisp/Forth/Rebol-like language on top of Go, so I could take advantage of its magnificent cross-compiler, but seeing that RISC-V is not one of Go's target architectures (mainly amd64 and ARM were of interest until now) that it's making me rethink the whole language layer thing. @bob @vertigo @jjg
That said, I do know that:
- Rocket core, KCP53000, and PicoRV32 are *not* susceptible to either Meltdown nor Spectre
- BOOM core, as it currently stands, *IS* susceptible to Spectre, but not to Meltdown.
@jjg @vertigo I read through the thread. I agree with Vertigo's assessment. Yosys is the state-of-the-art FLOSS toolchain. You can do a lot without ever touching a board. Of course, getting your hands on hardware can be a big part of the fun, so don't let me stop you.
If you do find yourself wanting to target hardware not supported by the FLOSS tools, I find that dedicating a virtual machine to the Xilinx or Altera tools into virtual machines works best. I use Vagrant at work to help with this.
I have an Altera/Terasic DE-1 on my desk that I'd like to work with as well, and getting Kestrel-3 running on the Cyclone II part it has should be much easier once it's known working on the two iCE40s first.
If I'd done the Cyclone II first, I'd have to figure out where to cleave the design, if it was at all possible.
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