Writing a Really Tiny RISC-V Emulator

[@DanielSMatthews]

It makes sense that you would be a RISC giver rather than a risk taker. 🙂Thanks for sharing.

[@CNLohr]

Oh I like that joke.

[@ioinfinity]

*\(^___^)/* 🐁

[@lpcamargo]

So cool, the whole thing fits the L1 cache of a modern processor with lines and lines to spare 😎

[@CNLohr]

Absolutely!

[@ioinfinity]

*\(^___^)/* 🦊

[@GiveAcademy]

I understand the whole being excited about a project… reach a monumental milestone and then hit the unsure if you will continue or quit while ahead haha. This is great work and you are very inspiring!!! I hope your curiosity continues to fuel your excitement for this project. Where this goes will be a great adventure. Keep up the awesome content! I have a feeling your channel is on the cusp of massive growth! Again great job!

[@CNLohr]

I did push it a litttle bit further, so I'm going to make at least one more video!

[@ioinfinity]

*\(^___^)/* 🐻

[@Greeegification]

Nice work! A fun step with emulators is adding in a gdb server/hooks so you can debug your emulated processor with breakpoints and watched variables just like on real hardware.

[@CNLohr]

I haven't gotten to it, but, that can totally be done using this emulator. The .h file can have overrides to facilitate this.

[@ioinfinity]

*\(^___^)/* 🐒

[@ioinfinity]

*\(^___^)/* 🦒

[@developandplay]

So happy you are back and working on stuff that I'm also interested in!

[@CNLohr]

It may only be for a bit but I'm gonna try to make it longer!

[@ioinfinity]

*\(^___^)/* 🐒

[@nethoncho]

This has helped me in planning my discrete TTL risc-v cpu. Thanks for posting

[@CNLohr]

Excellent! If I find any bugs I'll do my best to keep updating the template. Someone else already used my emulator as a template to write a RISC-V emulator in squirrel.

[@ioinfinity]

*\(^___^)/* 🐑

[@Maxjoker98]

Great video, as always. And I know that the ESP32 isn't the only place this could be useful, but you can absolutely boot noMMU Linux natively on an ESP32 with external PSRAM! I've got a kernel+buildroot setup that boots successfully in QEMU!

[@jesset2550]

Esp32 cannot use the psram as rwx it can only rw or rx from the ram it's a limitation of the hardware.

[@Maxjoker98]

@@jesset2550 While that's technically true, a) that does not mean it can't run Linux b) ESP32-S3, the newest ESP32, actually can just map 32MB of external RAM on *both* data and instruction bus. It works in QEMU already, I'm almost confident that I can get this to work on real hardware when I finally get a real ESP32 with PSRAM in my hands.

[@browaruspierogus2182]

​@@Maxjoker98 ESP32-S3 is not RiscV and has closed ISA protected by Xtensa. Esp is slowly replaced by chips like K210 or latest M1s that are superior and cheaper and much better. Espressif should make 64bit dual core riscv to make it easier for people but they care about money more

[@Maxjoker98]

​@@browaruspierogus2182 I never claimed the ESP32 S3 is RISC-V. Also the Xtensa ISA is well documented(You probably mean they should freely license it and their designs based on it). But I think what they should do is make the tiniest noMMU Linux capable SoC they can make, with Wifi and Bluetooth. I think there would be a market for that. And they already make the S3, which is capable of running Linux - I would love an ESP with RISC-V and PSRAM support, but that doesn't exist yet(It wouldn't have to be such a large and complex SoC as the K210, which is way more expensive).

[@browaruspierogus2182]

@@Maxjoker98 you probably didn't read posts on esp32 forum how many problems S3 has with managing f.ex LCD and Wifi/BT at same time. And how clunky and bas is psram. The design is really bad and they need to come up with better design

[@wi8shad0w]

Thumbs up for putting it together .. 👍🏼👍🏼

[@pedrorocha6203]

Nice one! Thanks for sharing, there's a lot of cool stuff to learn from this... cheers!

[@CNLohr]

This RISC-V emulator is like the gift that keeps giving. I just made two more videos on it, you should check my channel.

[@ioinfinity]

*\(^___^)/* :😺

[@jamesdoesthings1096]

Yay new upload!

[@maxime22000b]

I learnt a lot with this video, thanks for sharing. Hope you'll continue this project and make other cool stuff with it !

[@CNLohr]

I'm gonna be making at least one more, so be sure you're subbed!

[@maxime22000b]

@@CNLohr I am, for quite a long time already ;)

[@atypicalambience3487]

It's funny how many times I have rediscovered your channel learning about unrelated interesting things.

[@CNLohr]

I like finding out lots of unrelated interesting things!

[@iuri.castro]

Great project! love your videos, I hope you have more time to do them next year!

[@CNLohr]

We will see. I may or may not.

[@ioinfinity]

*\(^___^)/* 🐒

[@Anon.G]

Great video

[@JohnLauerGplus]

Dude, nice work on this!

[@CNLohr]

Thanks!

[@مقاطعمترجمة-ش8ث]

Nice to see come back with such beautiful way.

[@CNLohr]

Thanks. I "want" to keep making videos. It's just really hard to keep up the momentum.

[@0x1EGEN]

Haha this is brilliant!

[@qbqbqdbq]

solid work

[@vreascul]

maybe you don't want to put a red line at the bottom of the thumbnail as some people may think that they already watched the video

[@RagbagMcShag]

100%

[@vreascul]

also, great work!

[@CNLohr]

Osnap.

[@Weaseldog2001]

This is cool. I'm working on a very similar project for a RISC-V emulator, intended to be run as a sandbox inside of other applications. It'll be my second go at writing an emulated CPU. My first one used a made up machine instruction set, and I programmed in machine code by hand. When I paid attention to the RISC-V, I saw that my project was similar in may ways. In this second attempt, I am focused minimizing resources and and maximizing speed. After looking into other emulator projects, including yours, I see that the footprint is likely to be smaller than I anticipated.

[@CNLohr]

You might want to join my Discord, there's other RISC-Vers there. You can ping me at `cnlohr` on Discord.

[@MarquisDeSang]

Now try to implement prediction branching (it would probably slow down everything). Impressive stuff. Making a Risc-V emulator is something, maiking it actually run an OS is a different thing. I have the Neza Sipeed Risc-V SBC with Debian, Risc-V is the only possible future for everything. It is so well designed and their ABI makes everything faster because we know what registers to use.

[@CNLohr]

It almost certainly would slow things down, because there's already going to be branch prediction on the emulating hardware. Making that more sophisticated will just add abstraction overhead.

[@MarquisDeSang]

@@CNLohr It would probably still run faster than WASM

[@tablettablete186]

​@@MarquisDeSang lol

[@ioinfinity]

*\(^___^)/* 🐕

[@ioinfinity]

*\(^___^)/* 🦒

[@filipszkandera8267]

That is so awesome! This really encourages me to try to implement Linux on my RV32 system as well! (I'm not sure Its doable, but we'll see :))

[@CNLohr]

yess

[@紺野-純子]

actually insane

[@iamvfx]

Nicely done!

[@CNLohr]

Thanks!

[@guatagel2454]

Hi! Good to see you!

[@blablamannetje]

Amazing! Thank you.

[@dakshinatharindu7422]

Great work! Thanks for sharing

[@CNLohr]

Thanks for watching

[@joedoe3688]

that was impressive!

[@CNLohr]

Thanks.

[@raguaviva]

we missed you!

[@CNLohr]

I know it's just so hard to make time to make these videos.

[@JohnMitchellCalif]

wow, super interesting!

[@killiangrieg]

This is most impressive.

[@justanormalperson]

that's cool

[@_Localer]

Great video. I want to also write an emulator for learning

[@CNLohr]

You should! Hopefully I've pointed out a reasonable way forward!

[@lior_haddad]

That's really cool!

[@CNLohr]

Thanks

[@SlyEcho]

I tried to do a similar project, what helped me to get the decoding right was to print out the assembly and then it was pretty apparent if some number was wrong in comparison. 5:25 can you replace the ninja requirement with samurai? That one is pure C and Make. 14:04 xxd -e can show in little endian

[@CNLohr]

14:04 - I didn't know that. And - I can't update the way buildroot builds. At this point, I've just removed qemu from the build tree.

[@BryanChance]

Thanks for this video. I’m trying to learn to do something like this

[@CNLohr]

I think you'll like my channel then! This kinda stuff is my jam.

[@BrianG61UK]

Is the slowdown after initial stages of boot because I/O changes from polled to interrupt driven?

[@CNLohr]

I believe so. Or more specifically, that the Kernel appears to force a context switch because it assumes there "should" be no more room left in the output buffer even though there is.

[@lowercasebtwalso]

could you port this to webassembly then run Linux in the browser

[@CNLohr]

Someone already made a better RV32 emulator that runs in-browser. bellard.org/tinyemu/

[@SuperIva-DIY-RUS]

Wow! I wonder is it possible to run beowoolf cluster on blades based on risc-v (allwiner d1 for example)? And teach it to work with 10BASE-T for example? That is the case I would invest..

[@CNLohr]

probably!

[@bennguyen1313]

In case anyone is interested, there's a good video where George Hotz opens the spec, and starts writing a little RISC-V core in Python and in Verilog! BTW, with so many different flavors of Risc-V chip, each selecting the ISA options it wants.. won't the performance between chips be different, depending on the silicon technology, and how it implements those instructions?

[@CNLohr]

It absolutely will depend vastly. You could have 20MHz cores or 2GHz cores.

[@BrightBlueJim]

@@CNLohr Just as you can with ARM.

[@LogicEu]

Wow!

[@oglothenerd]

Time for me to rewrite it in Rust!

[@awuuwa]

impressive

[@CNLohr]

Thank you!

[@prozacgodretro]

So... a question... can a No-MMU version of linux work on a 386 in something like an unreal mode? I've been thinking about this for the past couple days as I also became aware of the no-mmu kernel stuff.

[@CNLohr]

As it stands, there's a little extra code that needs to be written per-architecture and there are still some unusual restrictions. But, the underlying answer is now "yes."

[@proxy1035]

i'm sorry if you mentioned it in the video but i didn't notice if you said that your Emulator follows the Unprivileged or Privileged Spec for RISC-V. having Linux run without an MMU is already pretty dope, but it would be even more amazing if it could also run on a CPU without seperate privilege levels (like Unprivileged RISC-V) and just enough CSR's to implement a few interrupts.

[@alexv1841]

thans for sharing! terminal font name please

[@CNLohr]

Mentioned in my other video description "AudioLink Mono" -- It's available on the VRChat AudioLink Discord

[@der.Schtefan]

Have you considered using ATDD (acceptance test driven design), especially with Cucumber, to test the specs of your CPU, before you implement it or run Linux on it? Or was the goal to make the source as small as possible, including "no unit test"? I think I would start getting nightmares designing a CPU emulation software without the ATDD for each operation.

[@kotcraftchannelukraine6118]

But what problem with adding MMU features to the emulator?

[@CNLohr]

Nope. It adds code. I need the smallest emulator that can boot Linux

[@fluffycritter]

MMUless Linux isn't anything new; 15 years ago a lot of embedded systems ran µClinux (aka uClinux), which was a fork of Linux specifically to not require an MMU. Really cool to see the idea alive and well, even if under a different project. And of course, really neat to see just how little code is actually necessary for RISC-V emulation (which isn't terribly surprising given the whole point to RISC-V).

[@CNLohr]

This is mainline. Not a fork. That's what makes it so cool.

[@fluffycritter]

@@CNLohr Yeah, apparently uClinux got merged in quite some time ago! So it's neat that it's still working.

[@erikwg3814]

"It's like an embeddable scripting language, except you can compile to it with gcc" That is indeed one way describe an entire RISC-V emulator xD

[@CNLohr]

I'm glad it was technically accurate.

[@BrightBlueJim]

Scripting languages are all virtual machines. However, the point of most scripting languages is to avoid some of the difficulties encountered with compiled languages. So what has been achieved? You can now write in C what you could have written in Python? Umm...

[@illegalcoding]

Hey! Great video! I'm just wondering what font you use for your terminal and text editor? It looks great!

[@CNLohr]

audiolink.dev/

[@Kuratius]

Would this be adaptable for a pi pico or does it require a lot of ram? I mean the linux kernel, less the emulator.

[@CNLohr]

There already is someone who's adapted it for the pico. It's called pico-rv32ima

[@oglothenerd]

Linux can run on something without an MMU!?

[@CNLohr]

Abso-lutely!

[@PaulTaylor1]

I love that font on your terminal emulator, what's it called please?

[@CNLohr]

It's in the description. audiolink.dev

[@teddyjuma2060]

Whats your terminal font?

[@CNLohr]

AudioLink Mono. It's by Llelloo in the VRChat AudioLink Discord Server

[@alexhajnal107]

@@CNLohr Is that available for download anywhere?

[@justgook]

+1 really interested

[@CNLohr]

@@justgook audiolink.dev/

[@justgook]

@@CNLohr thanks

[@belesiu]

Charles! Nice Good to see you. Nice video. Still at the place we worked together at a few years ago?

[@CNLohr]

Still hanging on. Though I feel a little like "hang In there" from S08E11 of the Simpsons.

[@belesiu]

@@CNLohr Mob war or free pretzels?

[@bart.grantham]

Where can one find "AudioLink Mono"?

[@CNLohr]

audiolink.dev/

[@l3p3]

I feel like we have the same weird special interests just again. Running linux on $1 mcu is what I dream of for a long time. Someone seen my nc10 netbook from 2009 that I upgraded with usb 3.0? xD

[@CNLohr]

I think there's a chance!

[@BrightBlueJim]

The magic is that the $1 MCUs are so CAPABLE. I remember not too long ago, when people doing stunts like booting Linux on an 8-bit machine ... in about an hour.

[@omercelebi2012]

I did not understand any point of this but watched. I know just Python and want to be familiar with C or Assembly. I would like to get tips where can I start RISC-V and do some simple projects.

[@CNLohr]

I am not sure if I have the best answer. You usually learn C before doing embedded.

[@thechadbuddha]

funfact: opencomputers2 a minecraftmod has risc V emulation

[@browaruspierogus2182]

Kendryte K210 is great but newer 3-core riscV mcu is out too - M1s

[@CNLohr]

Sadly RV64, so less interesting for my purposes.

[@browaruspierogus2182]

@@CNLohr guess you don't read specs at all...

[@x7mdNet]

We need to compile it to WebAssembly 😱

[@CNLohr]

It is painful that I'm not adding goto's to this code for this very reason.

[@x7mdNet]

@@CNLohr :(

[@LekKit_]

RVVM actually works with this, but perf is abyssmal ;D, and there is a way to do RISC-V->WASM JIT Sadly YT removes links to test page

[@fifthperson9777]

Does this mean i can run yolov5 on maixduino??

[@CNLohr]

y not

[@kamillatocha]

so did you made it run in VRchat ?

[@CNLohr]

Not... yet.

[@BrightBlueJim]

At first I thought, why would you want to emulate a microcontroller, on a microcontroller? But then I slowly started to realize, that it's all a matter of priorities. If you need more memory than your microcontroller has, then one option is to do swapping to an external device, to allow you to use more memory than you have, at the cost of a big reduction in performance. And sometimes it's worth the cost to be able to do things you otherwise couldn't. I say "external device", because I can just see people thinking to accelerate things by swapping to the on-chip Flash memory, and thereby wearing out their microcontrollers. I think Tesla had a problem like this. But if you have socketed Flash memory, in the form of SD cards or whatever the latest socketed format is, then what gets worn out is something that's replaceable. I worry about this a little on my laptop, since it runs a devil-may-care OS that swaps to a solid state drive that is a bit of a pain to replace. But then, by the time it wears that out, I'll be able (probably) to replace it with a bigger, faster SSD.

[@CNLohr]

Absolutely! There's a lot of weird reasons why it makes sense to virtualize your functionality. It's really nice to do with RISC-V because there's such good tooling and compilers to minimize the perf hit and frustration.

[@sorin.n]

Yeah, but can it run Doom? 😅 Amazing work! 👍

[@sellicott]

He just posted a screenshot of it running Doom in the Discord last night.

[@sorin.n]

@@sellicott I was just jocking but that's so cool!

[@CNLohr]

Check out my video I just posted! "But can it run doom?"

[@BrutalStrike2]

Got 10 IQ by just watching this video

[@CNLohr]

It'll fade, but I'll try to keep making videos to help keep the IQ up!

[@vincei4252]

Dude, you need a microphone pop-filter. Otherwise awesome stuff!

[@CNLohr]

I have one - it's just a few parts I re-recorded I didn't have it.

[@vincei4252]

@@CNLohr Ok, no worries. I noticed the audio got much better. I'm quite impressed with this project and I'm soaking up as much of it as possible. Build failed in subsystem for windows so I'll spin up a Linux VM to have a play. Thanks!

[@CNLohr]

@@vincei4252 let me know how it goes. I miiight try building it in WSL myself.

[@CNLohr]

@@vincei4252 Also see my note about needing to fix your paths for WSL.

[@vincei4252]

@@CNLohr ugh. KZbin. Sorry, I just saw your response. I wasn't notified. I was able to get everything working in a VM all the way to the command prompt. Superb stuff. Got sidelined on other things but EEVBlogs video about 10 cent RISC-V microcontrollers reminded me to come back here.

[@replikvltyoutube3727]

this could be useful to make DSLinux 2.0

[@CNLohr]

There are a ton of applications, and it's small and easy to use so give it a go!

[@RooMan93]

Maybe the og PSP can run Linux now

[@CNLohr]

Looks like it should have no issues.

[@sellicott]

First!

[@Jkauppa]

emulate the mmu inside the operating system

[@Jkauppa]

its just a memory access interface adapter

[@Jkauppa]

any law rule based will drain your iq if you rely on it

[@Jkauppa]

your life is death

[@Jkauppa]

what you praise shows what you believe in

[@CNLohr]

It would be toooo sloowwwww

[@paulk314]

This is awesome! I've been working on some similar hobby projects but nothing nearly as ambitious as trying to run Linux. I would not have imagined it could be run without an MMU (aside from in the "universal Turing machine" sense). I'm working on a simulator, assembler, and RTL implementation for FPGA. I want to get a basic RISC-V computer working on FPGA and then write a simple kernel for it. Now that I've seen this video, I'm more optimistic that I could at some point get Linux running on there, which would be amazing!

[@be-tech1741]

Very interesting..

[@CNLohr]

Do ett. You could also try to make things _even more stripped down_ and use an emulator as a test bed for the features you intend to implement.

[@kreuner11]

Ninja doesn't need Cmake, Cmake wants wither ninja or regular make

[@CNLohr]

It's how Python is configured to compile.

[@kreuner11]

@@CNLohr yeah but idk if you got it in the right order,

[@gvl610]

Will port it to Arduino Uno

[@CNLohr]

😬

[@BrightBlueJim]

Of course it will. It has SPI, so just rack up a whole bunch of PSRAM. Everything else is just software.

[@GeorgeTsiros]

python because there weren't enough scripting languages already

[@GeorgeTsiros]

line 227, system("") huh? that one of the common windows bullshitty undocumented stuff?

[@CNLohr]

Absolutely. I explained it in my doom deep dive video I just uploaded.

[@BadBoy65t]

Now remake the entire video in english please 😂😂

[@CNLohr]

This was the best I Can do.

[@SquidHominid]

Please invest in a pop filter. This video is VERY hard to listen to because of all of the plosives. Otherwise, amazing work! This is really cool and I look forward to seeing what you do next. :)

[@waldolemmer]

Boo

[@CNLohr]

Thanks! And I do have one, I just didn't use it for a few of the parts I had to re-record.

[@soyitiel]

Linux in a shader go 🧮

[@CNLohr]

Already been done. Just the question is can I do it better

[@scottfranco1962]

Nice.