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The Libre-SOC Hybrid 3D CPU [pdf] (fosdem.org)
48 points by ksec 27 days ago | hide | past | favorite | 20 comments



I might be missing something, but this seems awfully light on any real technical details, beyond "we intend to use this tech to create the HDL to make the chip with", and some rather high level strategic goals for the chip. Is there any work to show yet?

Glancing through the source repos, it looks like there's a decent amount of code written, so why not mention it or what it's doing so far? It looks at least somewhat non-trivial, so surely there's at least a basic demonstration.


we're a rather small technically-focussed team, 80% of us with Asperger's (!). right now, we can either focus on making the site look pretty, or we can focus on "getting it done".

if you'd like to see what was done up until around Nov 2020, i've a video of the first boot of the litex BIOS https://www.youtube.com/watch?v=72QmWro9BSE for example. however what would be really helpful would be offers of assistance. we've got funds available, so that's not a "we're looking exclusively for volunteers" thing

second answer: there appears not to be very much to show for it because we had to stop actual "development" work and do several months of planning on the Vectorisation system. however we couldn't start that unless we had a full and proper understanding of OpenPOWER, which was why we first had to do a basic OpenPOWER v3.0B core, and that's what's demo'd in the video.

hope that helps.


Awesome, thanks for the info and video :)

Really hoping this project succeeds. Maybe sometime I'll get a chance to work/play around with it a bit myself.


There's a lot of red flags, from NIH HDL generator language, to using an OoOE core for GPU tasks, to suggesting that you don't talk to your lawyer in the NLNet FAQ.

Wish them the best though, love to see as much libre silicon as possible.


There's a lot of red flags, from NIH HDL generator language, to using an OoOE core for GPU tasks, to suggesting that you don't talk to your lawyer in the NLNet FAQ

i ask people, if they want to help, not to waste money on talking to lawyers. specifically saying that if they really want to talk to a lawyer they should request that lawyer to donate their time as "pro-bono" due to the charitable funded nature of the project (NLnet is a Charitable Foundation).

i'm kinda stunned that two people actually genuinely asked this, rather than saying "i'll speak to my Accountant".

think about it: imagine being contacted by the Linux Foundation, offered some donations to do some work, and you respond, "oh, errr i demand the right to pay 30% of that charitably-sourced money you are offering me to my Lawyer in fees to check if it's ok to receive that charitably-sourced money", i mean, wtf?? :)

regarding using an OoO engine: you may be interested to review this:

https://www.pixilica.com/post/pixilica-s-founder-atif-zafar-...

we're trying something new, basically. that's down to being funded by NLnet to do innovative research.


You have to admit "don't talk to your lawyer about our pretty close to unique legal situation" is pretty sketch. There's plenty of situations where you can get pro bono legal advice, so encouraging people not to without knowing their situation sends the exact wrong message, that your arrangement might not stand up to legal scrutiny or comes with a bunch of unstated tradeoffs that might not be apparent.

Regarding OoO, I don't see anything in those slides that's in favor of an OoO GPU. And the fundamental die area tradeoffs between a GPU and an OoO core are different. OoO comes with the idea that you can spend 10x+ the die area on your dispatch logic than your ALUs and register file, and your GPU is designed to amortize the dispatch logic as much as possible against a sea of ALUs and register files since you have enough parallelism to just barrel schedule through massive amounts of threads. Both designs at their best keep their ALUs fed every clock, but a GPU just plain can dedicate much more die area to those ALUs meaning markedly more FLOPs per mm^2.


i appreciate the perspective. with Asperger's, i'm just literal and up-front. i do make it clear that Bob Goudriaans is a Chartered Account, specialising in International Tax Law. perhaps i should also mention that NLnet has been operating for 18 years, now?

no i didn't go into heavy details on the internal architecture, i did the study (with help from Mitch Alsup) on OoO for 5 months straight, back at the beginning of 2019. when he explained how easy it is to do multi-issue if you use Unary (bit-level) encoding on the Dependency Matrices, i went, "ok that's it, we're using that" :)

what the plan is, is to do instead of big.LITTLE, to do "long.FAT" :)

by that i mean, we will have one core that is high multi-issue and high clock rate, but the rest of the cores are MASSIVE on SIMD engines but light on issue (single or dual).

all still SMP, but some cores just absolute processing Monsters.

now, we'll still need a separate Texture Cache (in addition to I-Cache and D-Cache) because texture interpolation, we'll still need a pixel tile memory area, and so on

but we want to see how far we can get and still not have everything shipped over to a completely separate processor. that is madness, the driver development alone having to contain a full-on RPC mechanism. no wonder latency on GPU Shader execution is so bad on commercial CPUs.


migen is a very popular HDL in the Open Source FPGA space.


Robert Baruch on Youtube is building a (relatively simple) RISC-V CPU core using nMigen and it looks like a very nice tool to work with relative to other HDLs I've seen (though I've never had to actually use an HDL myself before so I may not be the best judge). Here's a playlist of the video series, with the earlier videos basically being an introduction to nMigen: https://www.youtube.com/watch?v=YgXJf8c5PLo&list=PLEeZWGE3Pw... His use-case is a bit unusual in that his ultimate target is discrete ICs instead of an FPGA, but he's using it to do formal verification of his core before he commits the time to building the schematics and laying out the PCBs.


At best, it's like the fourth or fifth most popular language among hobbyists not looking to tape out their designs (is there a single nMigen design that's been taped out?).

This would be be (by orders of magnitude?) the most complex design attempted in the language, which pushes it into NIH territory.


ours will be one of the first or second. Staf from Chips4Makers will be using nmigen-based infrastructure. the nice thing about being charitably-funded to do research is: it's not our personal money. NLnet has offered to pay for a 180nm tape-out, and we also qualify for Google-Skywater 130nm.

also, you may be interested to know: Sorbonne University has access to Cadence. after converting to Verilog, they ran our 180nm design through DRC and it passed 100%.

nmigen has some deterministic behavioural guarantees and much more which make it a far better choice. it happens to output Verilog which we can treat as a (readable) machine-code (assembler-like) intermediary.


My concern with nmigen with a taped out design isn't that you can get it to pass the PDK rules. It's the difficulty in creating a productive feedback cycle once simulation shows the inevitable bottlenecks in your design for each process node you're targeting.

It's for sure a solvable problem, but 9 time out of 10 the FOSS developers trying to push a new language into this space end up not meeting their actual "release a usable design" goals but instead spend all their time yak shaving the language. It's a classic nerd snipe in the space.


luckily, through yosys, conversion to Verilog is trivial. and yes, when we get to 22nm (etc) we'll need to license commercial tools from Cadence, Synopsis etc. we're setting up a commercial operation to do that.

right now we're in like "R&D mode", thankfully paid-for by NLnet.

i go into some detail about why we chose nmigen, and what can be done with it. it was not a "light decision", it was several months comprehensive review.

here's the point in the FOSDEM talk i just did: https://youtu.be/7rCeNzrCB_g?t=1939


Can you point to 3 instances of this happening?


"OpenPOWER ISA developed from PowerPC, with the RS6000in the 90s.

- NUMA approachIRaw brute-force performance pissed all over the competition at the time"

and

"Libre-SOC combines the best of historical processor designs,co-opting and innovating on them (pissing in the back yard of every incumbent CPU and GPU company in the process)."

This sounds like a lot of ego-driven cheat-beating.


Well, and perhaps the most ambitious quote:

"Libre-SOC can do the same tricks that IBM POWER10 and Apple M1 can. Intel (x86) literally cannot keep up."


>Ultimately it is a strategic business objective to develop entirely Libre hardware, firmware and drivers.

What is the thinking behind this? Build it and they will come?


not at all. we've two companies, one focussed on full transparency for Banking and other high-security environments, willing to sign Letters of Intent. we're looking for three more as it will make investment pretty straightforward.


Speaking of 3D chips. We live in 3D world but our chips are mostly 2D. Yeah I know there are layers but overall the chip is flat slab.

If we wanted to simulate 2D world in hardware, we could do it very efficiently on our CPUs and it would be infinitely scalable (assuming the world interacts mostly locally).

Here comes the interesting part: if we live in a simulation ran by higher-dimensional beings, we have to transform our physics into a form that would reveal some inherent dimension-ness of our physics, then if we find this number, the beings live in a world with one more dimension.

So for example if our physics seems to be 10 dimensional, the beings live in 11 dimensional world and their CPUs are 10 dimensional. They designed our physics to be only 10 dimensional so that they can run it efficiently on their CPUs.


The thermal aspects here are partly why our CPUs will probably be flatter than they are wide for quite some time.

Also, assuming these extra dimensions are like what we'd thing they'd be like we can simulate them - we sent probes all over the solar system using "2D" computing decades ago.




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