17 ms·

I don't know how CPUs work so I simulated one in code

892 points by boyter 7y ago

Circuits 7y ago
Modeling it in code is cool and all but you skipped out on all the fun and enjoyment (pain and suffering) of troubleshooting your own shitty wiring job by not doing this with discrete hardware on a proto board.
- djhworld 7y ago
  Oh yes, I've seen other people do similar things with 8-bit CPUs on a bunch of breadboards which is awesome, maybe I'll attempt that another time! I did suffer a different form of pain with trying to implement all the gates together in a GP programming language - that was probably a bad idea in hindsight!
  - Circuits 7y ago
    I have approached it in two different ways. One was with discrete hardware on breadboards. The other was with VHDL and an FPGA. Out of the two I would say the breadboard method was the most satisfying because at the end you can show it off as wizardry to the two people or maybe three people in your life who love you enough to be bothered by it.
- kabdib 7y ago
  I started out doing hardware, as you say. Lots of bad soldering (initially). Expensive smoke and shitty chips from Radio Shack that appeared to have had their magic smoke removed prior to being shipped to stores in packaging that definitely was not anti-static. Capacitors that blew up into confetti, diodes that became LEDs for a single, glorious instant. Poking around in the back of old teevee sets and somehow avoiding being electrocuted or thrown against the wall by 30KV waiting patiently in a circuit where the bleed resistor had cracked. Realizing that you're going to need another paper route to afford the buffer chips and board work. Learning that manufacturer data sheets are sometimes full of lies. Redesigning the support circuitry for the CPU to remove just one more chip. Failing a bunch of high school courses because you were writing a BASIC interpreter (in anticipation of working hardware, someday) instead of doing homework. Oh, I built a working computer, too. That was fun. But when at the end of that project you've got a processor and some RAM and a display sitting there in front of you, well, you realize that you don't really know what to do with the rig. Now what? Then I realized that I could do far more damage in software (at scale) than with hardware (just one-off workbench class disasters). And so . . .
  - djhworld 7y ago
    > Then I realized that I could do far more damage in software (at scale) than with hardware Haha, this was pretty much it for me too. I'd imagine going down the hardware route is a lot of fun with a lot of lessons learnt, but an expensive lesson. I might play around with some hardware stuff next though.
- jimmaswell 7y ago
  I remember in my college class that went over logic gates and all that, we had to make some circuits in a simulator program. I think we eventually made cycle-based adders in it. I'm pretty sure you could make a full CPU like that too.
gvand 7y ago
Nice project!
naringas 7y ago
there's also the series of youtube videos by Ben Eater in which he builds a breadboard computer. link: https://www.youtube.com/playlist?list=PLowKtXNTBypGqImE405J2565dvjafglHU https://www.youtube.com/playlist?list=PLowKtXNTBypGqImE405J2...
baybal2 7y ago
Especially for people in line of web development. Take a look to see how simple is working of a CPU, and by how many MAGNITUDES does the code size grow when any modern "programming paradigm" is involved. Programs that are brought down to the absolute minimum of arithmetic and logical operations in assembler can often run thousand times faster than when written in higher level languages. I remember I was shown how a classical computer science problem called "Sisyphus dilemma" can be done in a single logic instruction, instead of a kilobyte long program in Java that makes the smallest solution possible when no binary operations are allowed.
- Aromasin 7y ago
  And that's when you start to fall into the deep rabbit hole that is FPGA's and VHDL/Verilog, all in the pursuit of that need for speed.
- adrianN 7y ago
  I don't think you lose three orders of magnitude of performance with a high level language. What a modern C compiler produces with a little help from the programmer should be reasonably close to what you can achieve by hand. Even slow languages like Python are not a thousand times slower than C. Maybe a hundred times.
  - lm28469 7y ago
    > What a modern C compiler produces with a little help from the programmer should be reasonably close to what you can achieve by hand. Unless you're an expert in ASM / have an unlimited amount of time / work on an extreme edge case I'd say the compiler will beat a human 99.9/100
    - dspillett 7y ago
      I'm not sure I'd go as far as "beat a human 99.9/100", certainly not beat by a significant amount, but definitely "at least equal a human 99.9/100". Of course that 1‱ where the human wins could be large wins, but then you have to consider if they are in positions that actually matter i.e. tight loops.
guhcampos 7y ago
It's an impressive, yet symptomatic feat. With more and more people getting into coding and languages of higher and higher levels, less of us are turning to the lower levels of computer science. Lots of developers did not study CS at all and the ones who did mostly neglected the computer architecture classes - myself included. Sometimes I stop and wonder that most of my low level compute knowledge comes as mere luck because I ended up working for the EDA industry for a few years. If I had not, I'd be a computer scientist with close to no understanding of how a computer actually works. We should all know our HDL's.
- baybal2 7y ago
  > Lots of developers did not study CS at all I do feel the same. A lot of "computer science" degrees are in fact just basic programming ones, and that often goes to masters, and rare cases PhD level degrees. It is a common critic from industry that "computer science does not teach how to code," and I see too many universities seemingly taking it these days. It is ironic how once computing science was once a road to unemployability and coding was all rife, but now companies don't want to hire people without degrees to do menial jobs like webdev.
  - Klathmon 7y ago
    Can we try to stop this gatekeeping and putting down some jobs as if they are "menial". A lot of the webdev work I've done has been significantly more challenging and technically difficult than most of the C work I've done. That's not to say C is "easier", it's not, but it is different. I've seen shitty devs in all areas, and I've worked menial jobs both in webdev and at the embedded C level (I had to write C code to display a custom font on a shitty LED display, that was easily the most boring job I've ever done).
    - vectorEQ 7y ago
      i don't do web stuff because it's horrible frustrating and difficult. C is nice, i love it as it matches the pc platform and you can debug it normally etc. A lot of people like to hate on 'frontent developers' or 'full stack javascript developers' or w/e but you are right. whatever floats your boat will be 'better' and 'more logical' than whatever sinks your ship. for me thank sinking is caused by scipring and CSS. for others that might be C.
ameyv 7y ago
This is really good resource.. Thank you
Jipazgqmnm 7y ago
https://www.nand2tetris.org/ https://www.nand2tetris.org/
eatonphil 7y ago
Going through a similar phase, though this is way further along. :) I had a great course in college on computer architecture that culminated in a processor in Logisim that could run fairly complex programs. (I recommend the Harris and Harris textbook for a surprisingly light/easy introduction [0].) But that was a while ago and I've never done anything for x86/amd64. I started working on an emulator [1] a few weeks ago but it interprets Intel x86 assembly rather than ELF files. I found this a great way to get started since parsing text is easier and the instructions you need to get a basic C program (compiled to assembly) running take an hour or two: call, push, pop, add. You can shim _start in without having to implement syscalls. Conditional jumping and syscalls took another weekend or two and now it can run some basic fibonacci C programs. I also had to build a graphical debugger for it to see what was going on... I will probably move to reading ELF files soon. I'll be writing up the process in a series on x86/amd64 emulator basics. [0] https://www.goodreads.com/book/show/2558730.Digital_Design_and_Computer_Architecture https://www.goodreads.com/book/show/2558730.Digital_Design_a... [1] https://github.com/eatonphil/x86e https://github.com/eatonphil/x86e
- bogomipz 7y ago
  Your emulator project is really neat. I would love to see more documentation on the design and process of it. The notes.md file was pretty spartan. Thanks for sharing. Cheers.
  - eatonphil 7y ago
    Will post back once I start the series!
  - eatonphil 7y ago
    Here's the first post: http://notes.eatonphil.com/emulator-basics-a-stack-and-register-machine.html http://notes.eatonphil.com/emulator-basics-a-stack-and-regis...
- djhworld 7y ago
  This is awesome, will look forward to following its progress
flanbiscuit 7y ago
Very cool! I had the same thoughts as you and bought "From Nand to Tetris"[1] a while ago but I did not get as far as you. You've inspired me to pick it back up and finish the book. Curious if you decided to use "But How Do It Know?" over "Nand to Tetris" for any specific reason or were you just not aware of the latter. 1. https://www.nand2tetris.org/ https://www.nand2tetris.org/
- alpaca128 7y ago
  Just a few days ago I found NandGame, which is a browser game where you build a computer starting with just the Nand gate and using only components you already built for the next one. Pretty cool idea.
- djhworld 7y ago
  Hi author here! I actually didn't set out on building anything, it all happened organically! I honestly cannot remember why I chose the book, I think I just saw the blurb and figured it was good enough to read. It was only when I was a couple of chapters in that I figured I could probably whip something up in code :)
  - Hnrobert42 7y ago
    Hello author. I just wanted to heartily thank you for trying this and writing a post about it. I love seeing people pursuing technology for the sheer joy of it. Staring at the blank whiteness of an unwritten post, one wonders whether anyone else will notice or care what words will come tumbling out. But through your post, your work is multiplied. It is inspiring. So, again, thank you.
    - djhworld 7y ago
      No worries, thanks for the kind words. I got some great feedback from friends and colleagues before publishing it so thanks to them too :)
- robbbbbbbbbbbb 7y ago
  +1 for Nand to Tetris. As someone who came to computing through high level software and a little later than many (I wasn't dismantling appliances at age 5 like you hear in a lot of people's origin stories) this was a really empowering ground-up introduction to hardware architecture. One of the few Coursera courses [1] I actually finished and found rewarding, challenging and fun throughout. 1. https://www.coursera.org/learn/build-a-computer https://www.coursera.org/learn/build-a-computer
xigency 7y ago
> So I’m trying to get a better understanding of this stuff because I don’t know what L1/L2 caches are, I don’t know what pipelining means, I’m not entirely sure I understand the Meltdown and Spectre vulnerability papers. I wouldn't discourage anyone from learning about hardware from implementing gates or even looking at simple 8-bit CPUs, but if you are interested in learning how modern caches and pipelines work, there is a free Udacity course that goes into excellent detail [0]. You can also find the lecture videos on YouTube. This is originally an online course at Georgia Tech and the professor does an excellent job teaching these concepts. [0] https://www.udacity.com/course/high-performance-computer-architecture--ud007 https://www.udacity.com/course/high-performance-computer-arc...
- dr_zoidberg 7y ago
  There's a very good article [0] that makes rounds here very now and then. It gives a very good explanation of many of those concepts, while remaining understandable for those that haven't taken CPU design courses. [0] http://www.lighterra.com/papers/modernmicroprocessors/ http://www.lighterra.com/papers/modernmicroprocessors/ Edit: It'd be great a 2019 refresh (last update is from 2016) talking about Ryzen and the newer Intel designs.
  - djhworld 7y ago
    Bookmarked, thanks for the link, I think it will help me with the next step
- taormina 7y ago
  I took this class at Georgia Tech as an undergrad and I also highly recommend it for the material. We had a chain of CS classes leading up to it (2110 -> 2200 -> 4290) on the undergrad side, but when I took it, this course was actually cross-listed as both an undergrad and graduate CS and ECE class (so CS 4290/6290 and the same sort of thing for the ECE major were all in the same literal lecture hall). Of course, most CS students were only taking this if they were in the System & Architectures thread (or maybe Devices?), but most CS students had to at least take up to CS 2200 (Systems & Networks, which basically took the concepts up to "Build me a working 1 CPU computer", whereas this class took the next steps from "Okay, so how do we do better than 1 instruction per cycle?"). Multi-core processors are really cool! I frequently take for granted that most people don't have this foundational knowledge. The basics come up more than you'd think, especially when provisioning the right hardware for the task.
js2 7y ago
> However, after making my way through But How Do It Know? by J. Clark Scott, a book which describes the bits of a simple 8-bit computer from the NAND gates, through to the registers, RAM, bits of the CPU, ALU and I/O, I got a hankering to implement it in code. Speaking of code, another excellent book along these lines is Code: The Hidden Language of Computer Hardware and Software by Charles Petzold. http://www.charlespetzold.com/code/ http://www.charlespetzold.com/code/
- heinrichhartman 7y ago
  yes, that's notably the only publication by Microsoft Press, I can recommend ;)
  - segfaultbuserr 7y ago
    > the only publication by Microsoft Press Really? https://www.microsoftpressstore.com/store/browse/programming https://www.microsoftpressstore.com/store/browse/programming
    - C4stor 7y ago
      Odds are the last comma is a typo ^^
      - segfaultbuserr 7y ago
        Aha, I see what you meant. Quite interesting to see how ambiguity can be created by a mere comma in real life.
        deleted 7y ago
        [deleted]
  - Insanity 7y ago
    I'm pretty sure Code Complete2 is a publication by Microsoft Press. I'd say that's a pretty well known and well worth reading book.
tamaharbor 7y ago
“See all that stuff in there, Homer? That’s why your robot never worked.” - Marge Simpson
pjc50 7y ago
> https://github.com/djhworld/simple-computer/blob/master/cpu/cpu.go#L763 https://github.com/djhworld/simple-computer/blob/master/cpu/... The author themselves points out that a "big pile of gates" is not the best approach here, but I'm kind of surprised that at no point did they attempt to build another representation of the circuit and either execute it in a table-driven way, or write a short script that spits out go for compilation.
- gnode 7y ago
  > but I'm kind of surprised that at no point did they attempt to build another Perhaps because the existing implementation had already served its purpose - an educational exercise to understand CPU design, and not an instruction-level emulator or transcompiler.
- djhworld 7y ago
  Thanks for the feedback, these are some good ideas if I was do do this again. I'm sorry you didn't think I took the best approach.
thrower123 7y ago
I still think the single best course I took in college was my computer architecture course. We built an entire 8-bit CPU up from individual gates over the course of the semester in Logisim[1], to the point where we could compile a limited version of C down to the machine code for our simulated processor and load it into the simulated main memory and run it. I'm incredibly glad there was that hands-on component to the course, rather than just the theoretical textbook and lectures learning; it was hard as hell, and I actually ended up dropping it the first time and taking it again later, but at the end I actually felt like I kinda knew what was going on. Pointers were never mysterious again, at least. [1] http://www.cburch.com/logisim/ http://www.cburch.com/logisim/
blago 7y ago
I took an architecture class back in college and the first time we met, the professor gave us a couple of programs described in plain English. One of them was basically sorting, and the other one something else. Each of us spent the rest of the semester picking an instruction set, designing a system, writing an emulator, and writing the code that would perform the tasks described on the first day. I went a little overboard and created a C backend for the emulator along with an in-browser JS client that was pretty much a full-blown machine language IDE and debugger. Needless to say, this feature creep didn't end well. I barely made it work well enough to get an ok grade but I learned that overconfidence can be more dangerous than the lack of. Here's what I was able to salvage from the front end on short notice: http://blago.dachev.com/~blago/CS-535/stage_2/src/web/ http://blago.dachev.com/~blago/CS-535/stage_2/src/web/ It's using ext.js which was pretty cool at the time.
- Hendrikto 7y ago
  > I barely made it work well enough to get an ok grade but I learned that overconfidence can be more dangerous than the lack of. That is a very important lesson.
  - w0utert 7y ago
    Yeah, reminds me of the time I had to write a BSP tree builder as a course assignment, and ending up spending 2 months writing an OpenGL renderer + an importer for the Apple QuickDraw 3D API instead (hint: don't try to do that, it's almost a full object-oriented programming language in itself if you want to support even a moderately complex model). All just because I found some nice architecture models that were only available in QD3D format, and I was convinced it would only take me a few hours to read them... I only got the brilliant idea of just converting them to something simpler like .3DS after I already finished the assignment >_<
- lioeters 7y ago
  > I went a little overboard and created a C backend for the emulator along with an in-browser JS client that was pretty much a full-blown machine language IDE and debugger. Haha, this made me smile. I can totally relate to that ambitious line of thinking: given a task to solve, you imagined the logical next steps, to build an environment for solving that general class of tasks. Great lesson about feature creep, but I also think that kind of vision and ambitious problem-solving can be valuable in the long term, if it works the whole community/ecosystem can benefit.
gilbetron 7y ago
(Way) back in college, we had been learning high-level programming concepts (UI, OS, Compilers, Algorithms, etc), underlying math behind computing, and physics up through circuits. My favorite course was Computer Architecture which was set up to pull everything together, mostly through a series of simulated computer projects, until, at the end, you realized you knew how a computer worked from math, through physics, and up to what the person interacted with. One of my favorite educational experiences ever. The Professor (Yale Patt) was a really interesting guy, great storyteller, and still actively worked with Intel. I also thought he was really friendly, turns out he just liked talking my girlfriend at the time and I was a tag-along ;)
- sanderjd 7y ago
  This was my favorite part of college too. I think it was near the end of a really good networking class I took maybe my junior year when I distinctly remember chatting on AIM and thinking about how I could visualize approximately how my key presses were going from the hardware through the OS into memory into instructions on the CPU executing the application back out onto my screen and across the network to a server and on to my friend's machine for the reverse trip. It was a powerful moment. Of course as I've gone further through my career I've realized how far off my approximation was because everything is even more complex in the details, but I still think it was a fundamentally valid and valuable moment. This is one reason I'm ambivalent about the skepticism around computer science / engineering programs as a prerequisite for a career in software development. It bums me out to think of people toiling at this work without experiencing that kind of bottom-up knowledge of computing. But I think this is largely a projection of my own personality on others; that would be a bummer for me, but I think many people don't care about any of that and just want to do valuable work for good pay.
- elamje 7y ago
  Glad to hear from another survivor of Dr. Patts class. I took him for intro to computing first semester of college with no programming experience and I got wrecked by his class, but most of the content has stuck with me up through my career!
levelist_com 7y ago
Check out the following: The Elements of Computing Systems: Building a Modern Computer from First Principles https://www.amazon.com/Elements-Computing-Systems-Building-Principles-dp-0262640686/dp/0262640686/ref=mt_paperback https://www.amazon.com/Elements-Computing-Systems-Building-P...
ixtli 7y ago
I took a computer architecture course in undergrad and they had us make an ARM emulator similar to this in c++. It was extremely illuminating.
- djhworld 7y ago
  Cool. I always find that "learn by doing" works best in these sorts of things :)
balls187 7y ago
The final for Computer Architeture had us building an 8-bit CPU. It was a multiweek project, starting with designing the instruction set leading up to building the CPU in software implementing bubble sort in assembly. The first and only time I had to do an all nighter (2 actually) in college was due to that project. Two days before the final presentation, the CPU didn't work. After a few clock cycles the memory would contain garbage. I ended up rebuilding it from scratch debugging every step of the way only to find out the 1-bit mux (a primitive supplied with the software) was wired backwards. 0 corresponded to the B input, and 1 selected the A input. Once I correct that, the CPU worked like a charm, we nailed the final preso, and I slept for 16 hours.
- cobookman 7y ago
  Had to do the same assignment. I highly recommend doing it. Was the most painful thing I ever did in college, but it taught me so much about how processors work, and how to code in C.
  - _han 7y ago
    Is there a public resource somewhere that describes the assignment/gives some guidelines? I would like to give it a try.
    - cweagans 7y ago
      https://www.nand2tetris.org/ https://www.nand2tetris.org/ goes through the same process. Highly recommend!
      - BanazirGalbasi 7y ago
        The game MHRD (MicroHard) offers the same content, but in an interactive environment. I haven't gone much into it yet so I don't know how the end content compares to Nand2Tetris, but a lot of people say they're different methods of teaching almost identical content.
blattimwind 7y ago
> I don't know how CPUs work Guess introductory courses in universities aren't useless after all.
russellbeattie 7y ago
Ben Eater has a series of videos where he builds an 8 bit computer using actual chips. He starts from first principals and it's pretty amazing to see it come together. Definitely worth watching. Building an 8-bit breadboard computer!: https://www.youtube.com/playlist?list=PLowKtXNTBypGqImE405J2565dvjafglHU https://www.youtube.com/playlist?list=PLowKtXNTBypGqImE405J2...
lqet 7y ago
Nice work. Somewhat related to the Megaprocessor by James Newman [0] [0] http://www.megaprocessor.com/progress.html http://www.megaprocessor.com/progress.html
- djhworld 7y ago
  I watched the Computerphile episode about this on Youtube when I was in the midst of the project, apparently it's at a Computer History museum in Cambridge now, I really should find the time to go!
afpx 7y ago
This is very cool. It would be so fun to run qemu on it. https://www.qemu.org/ https://www.qemu.org/.
- djhworld 7y ago
  I think the machine would need to be much _much_ faster, with the stack pointer register + a few extra instructions to even attempt a project like that hahahahaha
Zrdr 7y ago
Congrats ! This reminds me of this amazing computer done in the cellular automaton Wireworld. https://www.quinapalus.com/wi-index.html https://www.quinapalus.com/wi-index.html
vectorEQ 7y ago
cool project and nice writing style on the blog. awsome!
hawkjo 7y ago
Quick shout out to NAND Game, a version of this laid out as a computer game. Delightful, free, web-based. http://nandgame.com/ http://nandgame.com/
- hathawsh 7y ago
  That is awesome. I plan to challenge my kids to finish that game this summer.
anderspitman 7y ago
I went back to school for CS after 6 years of professional programming. Just for being guided through logic gates, assembly, and implementing a simple CPU in an FPGA I consider it well worth the time and money. The point when I realized I finally understood (on a surface level) everything from the electrical signals to my JavaScript reminds me of when I finished the last video of Khan Academy's series on Euler's formula and "understood" it, if only for a moment.
arcticbull 7y ago
I did this too, when I was in college. I implemented a gameboy CPU emulator. Then I wanted to know how FPGAs work so I implemented a Chip-8 CPU on an FPGA. Once I clean it up, I'll throw it up on my GitHub and maybe write up a quick medium post. This is exactly how I learn: I don't know how something works, so I make one.
- djhworld 7y ago
  > This is exactly how I learn: I don't know how something works, so I make one. Uh huh, the FPGA Chip-8 thing sounds awesome! Definitely post about it!
- bogomipz 7y ago
  Please do, this would be an interesting read. Cheers.
mar77i 7y ago
I got this link yesterday or so. I breezed through it until the memory latch: http://nandgame.com/ http://nandgame.com/
- djmips 7y ago
  Try this! It's fun!
- rdc12 7y ago
  Did you manage to make the latch in the end? I would imagine feedback would be a tricky subject to try learn without help.
nlowell 7y ago
Implementing a CPU simulation is a classic college exercise, as you can see in these comments. Super valuable based on how memorable it was for everyone! It really helps de-mystify computers.
peter303 7y ago
Thats how Gates and Allen wrote their BASIC interpreter for the Altair microcomputer and started MicroSoft. They did not have access to a working 8080 microcomputer so they simulated one on a Harvard mainframe from a machine language specification. Bill took the interpreter by punch tape to MITS in Albuquerque. And legend has it their BASIC worked only after an hour of fiddling.
- djhworld 7y ago
  That's such a cool story haha. Not sure if my thing is remotely close to that, but nice to know I'm standing on the shoulder of giants :)
floor_ 7y ago
Making a chip-8 emulator is a reasonable project for those who are interested.
- merlincorey 7y ago
  I'm in the final stretches of mine right now, in fact. The article describes an 8 bit CPU with 17 instructions. CHIP-8 is an 8 bit CPU with 31 instructions, but crucially, it has a large amount of documentation[0] and a nice corpus of ROMS available[1] making it a bit easier as you don't have necessarily write your own programs for a CPU you don't fully understand yet. [0] See http://devernay.free.fr/hacks/chip8/C8TECH10.HTM http://devernay.free.fr/hacks/chip8/C8TECH10.HTM among many other resources [1] For example this archive of the now defunct chip8 archive site https://github.com/dmatlack/chip8/tree/master/roms https://github.com/dmatlack/chip8/tree/master/roms
  - djhworld 7y ago
    Just looking at the docs, those 31 instructions would definitely help a lot, along with the stack pointer register. I'd definitely recommend doing something like that (not at the logic gate level though - too slow) but an emulator is a fun project to tackle. I wrote my Gameboy emulator first which is a bit more complicated than chip-8 and at the time the documentation was a lot more varied.
ibeckermayer 7y ago
I'm working on a similar project, implementing the architecture described in this book (https://www.nand2tetris.org https://www.nand2tetris.org). Ultimately I hope to implement it on an FPGA with attached keyboard and screen and actually use it to compute stuff: https://github.com/ibeckermayer/Nand2TetrisFPGA https://github.com/ibeckermayer/Nand2TetrisFPGA
- djhworld 7y ago
  Will look forward to following its progress!
  - ibeckermayer 7y ago
    Thank you :)
- mikevin 7y ago
  Nice project. I've finished most of the course (up until the compiler because that's where it became too familiar) and I'm now redoing it on an actual fpga. It's a great learning experience and I can fully recommend keeping at it, it's one of the most rewarding projects I've done. Actually bought a Pynq Z2 last week to have some peripherals to connect and to drive it easily. Might put it up github too.
  - ibeckermayer 7y ago
    Nice. I looked around online and it seems like others have attempted something like this but I didn't find any project that looked complete. I have a Basys 3 board which has VGA and USB I/O, so I hope to actually get from Nand to actually playing Tetris on my homespun platform.
sehugg 7y ago
Shameless plug -- hardware engineering students are using the online 8bitworkshop IDE to study and design custom CPUs in Verilog: https://8bitworkshop.com/redir.html?platform=verilog https://8bitworkshop.com/redir.html?platform=verilog
elamje 7y ago
Any Yale Patt alums here?
- kickopotomus 7y ago
  EE360N Labs all over again. Tangentially, does anyone know what Patt has had to say about Meltdown/Spectre? Speculative execution was/is his bread-and-butter if I remember correctly.
- GrumpyYoungMan 7y ago
  Giant beard? Fond of telling people that one of his grad students was the chief architect of the Pentium III? Yeah, I remember his comp. arch. classes fondly.
dustfinger 7y ago
People who are interested in building their own computer might enjoy the Bitwise [1] project over at the Handmade Network. [1]https://bitwise.handmade.network/ https://bitwise.handmade.network/
nstart 7y ago
As a layman on this topic, I'm curious about the difficulty around this project: It seems like a lot of people have gone through similar experiences of building an 8 bit CPU simulator/emulator. Curious why it's not 64 bits. I can guess the answer is "it's hard". I'm just wondering where the difficulty lies. Is it in the standards? The mechanical feasibility of connections? Actual limitations of building a 64 bit emulator on a machine powered by a 64 bit processor? Apologies if the question seems obvious. I come into this knowing next to nothing and I could probably find the answer with some research of my own. Just wanted to ask the community for thoughts here ️
- dpe82 7y ago
  Designing a simple 64 bit CPU is not really more work than a simple 8 bit processor. 64 bit CPUs tend to have more features than just wider registers though.
- djhworld 7y ago
  For this project? It wouldn't have been difficult to upgrade the machine to 64-bit, it's really just a matter of increasing the bus width and register size. But it would slow it down massively due to me writing it in a general purpose programming language and passing around booleans everywhere, there's a lot of for loops that copy things in and out of buses and I would have to increase the size of the ALU to accomodate the bigger numbers.
madrox 7y ago
Reminds me of the early days of unmodded Minecraft when someone made a CPU in game with lots and lots of redstone. It really makes otherwise arcane concepts accessible. Super cool!
DonHopkins 7y ago
I love how you can actually see the different parts of Guy Steel's Lisp Microprocessor, which he designed in Lynn Conway's legendary 1978 VLSI System Design Course at MIT. http://ai.eecs.umich.edu/people/conway/VLSI/MIT78/MIT78.html http://ai.eecs.umich.edu/people/conway/VLSI/MIT78/MIT78.html The Great Quux's Lisp Microprocessor is the big one on the left of the second image, and you can see his name "(C) 1978 GUY L STEELE JR" if you zoom in: "Guy Steele: LISP microprocessor (LISP expression evaluator and associated memory manager; operates directly on LISP expressions stored in memory)." http://ai.eecs.umich.edu/people/conway/VLSI/InstGuide/MIT78chip%20photo-2%20L.jpg http://ai.eecs.umich.edu/people/conway/VLSI/InstGuide/MIT78c... And here is a map of the different parts of the Lisp microprocessor: https://imgur.com/zwaJMQC https://imgur.com/zwaJMQC Here is the chalk board where they kept track of all the student's projects and where they would go on the chip: http://ai.eecs.umich.edu/people/conway/VLSI/MIT78/Status%20Em.jpg http://ai.eecs.umich.edu/people/conway/VLSI/MIT78/Status%20E... And the layout of the chip with everyone's project (with the big Lisp microprocessor standing out at the lower left): "The final sanity check before maskmaking: A wall-sized overall check plot made at Xerox PARC from Arpanet-transmitted design files, showing the student design projects merged into multiproject chip set." http://ai.eecs.umich.edu/people/conway/VLSI/MIT78/Checkplot%20s.jpg http://ai.eecs.umich.edu/people/conway/VLSI/MIT78/Checkplot%... This is a photo of one of the wafers they made, with lots of chips: "One of the wafers just off the HP fab line containing the MIT'78 VLSI design projects: Wafers were then diced into chips, and the chips packaged and wire bonded to specific projects, which were then tested back at M.I.T." http://ai.eecs.umich.edu/people/conway/VLSI/MIT78/Wafer%20s.jpg http://ai.eecs.umich.edu/people/conway/VLSI/MIT78/Wafer%20s.... And here the classic paper about it, "Design of a LISP-based microprocessor" by Guy Lewis Steele, Jr. and Gerald Jay Sussman: https://dl.acm.org/citation.cfm?id=359031 https://dl.acm.org/citation.cfm?id=359031
ZedIsNotDead 7y ago
Modern problems require modern solutions.
cptnapalm 7y ago
You can also do this with UNIX pipes and a few small C programs, apparently. https://www.linusakesson.net/programming/pipelogic/index.php https://www.linusakesson.net/programming/pipelogic/index.php

892 points by boyter 7y ago

Modeling it in code is cool and all but you skipped out on all the fun and enjoyment (pain and suffering) of troubleshooting your own shitty wiring job by not doing this with discrete hardware on a proto board.

djhworld 7y ago
Oh yes, I've seen other people do similar things with 8-bit CPUs on a bunch of breadboards which is awesome, maybe I'll attempt that another time! I did suffer a different form of pain with trying to implement all the gates together in a GP programming language - that was probably a bad idea in hindsight!
- Circuits 7y ago
  I have approached it in two different ways. One was with discrete hardware on breadboards. The other was with VHDL and an FPGA. Out of the two I would say the breadboard method was the most satisfying because at the end you can show it off as wizardry to the two people or maybe three people in your life who love you enough to be bothered by it.
kabdib 7y ago
I started out doing hardware, as you say. Lots of bad soldering (initially). Expensive smoke and shitty chips from Radio Shack that appeared to have had their magic smoke removed prior to being shipped to stores in packaging that definitely was not anti-static. Capacitors that blew up into confetti, diodes that became LEDs for a single, glorious instant. Poking around in the back of old teevee sets and somehow avoiding being electrocuted or thrown against the wall by 30KV waiting patiently in a circuit where the bleed resistor had cracked. Realizing that you're going to need another paper route to afford the buffer chips and board work. Learning that manufacturer data sheets are sometimes full of lies. Redesigning the support circuitry for the CPU to remove just one more chip. Failing a bunch of high school courses because you were writing a BASIC interpreter (in anticipation of working hardware, someday) instead of doing homework. Oh, I built a working computer, too. That was fun. But when at the end of that project you've got a processor and some RAM and a display sitting there in front of you, well, you realize that you don't really know what to do with the rig. Now what? Then I realized that I could do far more damage in software (at scale) than with hardware (just one-off workbench class disasters). And so . . .
- djhworld 7y ago
  > Then I realized that I could do far more damage in software (at scale) than with hardware Haha, this was pretty much it for me too. I'd imagine going down the hardware route is a lot of fun with a lot of lessons learnt, but an expensive lesson. I might play around with some hardware stuff next though.
jimmaswell 7y ago
I remember in my college class that went over logic gates and all that, we had to make some circuits in a simulator program. I think we eventually made cycle-based adders in it. I'm pretty sure you could make a full CPU like that too.

gvand 7y ago

Nice project!

naringas 7y ago

there's also the series of youtube videos by Ben Eater in which he builds a breadboard computer. link: https://www.youtube.com/playlist?list=PLowKtXNTBypGqImE405J2565dvjafglHU https://www.youtube.com/playlist?list=PLowKtXNTBypGqImE405J2...

baybal2 7y ago

Especially for people in line of web development. Take a look to see how simple is working of a CPU, and by how many MAGNITUDES does the code size grow when any modern "programming paradigm" is involved. Programs that are brought down to the absolute minimum of arithmetic and logical operations in assembler can often run thousand times faster than when written in higher level languages. I remember I was shown how a classical computer science problem called "Sisyphus dilemma" can be done in a single logic instruction, instead of a kilobyte long program in Java that makes the smallest solution possible when no binary operations are allowed.

Aromasin 7y ago
And that's when you start to fall into the deep rabbit hole that is FPGA's and VHDL/Verilog, all in the pursuit of that need for speed.
adrianN 7y ago
I don't think you lose three orders of magnitude of performance with a high level language. What a modern C compiler produces with a little help from the programmer should be reasonably close to what you can achieve by hand. Even slow languages like Python are not a thousand times slower than C. Maybe a hundred times.
- lm28469 7y ago
  > What a modern C compiler produces with a little help from the programmer should be reasonably close to what you can achieve by hand. Unless you're an expert in ASM / have an unlimited amount of time / work on an extreme edge case I'd say the compiler will beat a human 99.9/100
  - dspillett 7y ago
    I'm not sure I'd go as far as "beat a human 99.9/100", certainly not beat by a significant amount, but definitely "at least equal a human 99.9/100". Of course that 1‱ where the human wins could be large wins, but then you have to consider if they are in positions that actually matter i.e. tight loops.

guhcampos 7y ago

It's an impressive, yet symptomatic feat. With more and more people getting into coding and languages of higher and higher levels, less of us are turning to the lower levels of computer science. Lots of developers did not study CS at all and the ones who did mostly neglected the computer architecture classes - myself included. Sometimes I stop and wonder that most of my low level compute knowledge comes as mere luck because I ended up working for the EDA industry for a few years. If I had not, I'd be a computer scientist with close to no understanding of how a computer actually works. We should all know our HDL's.

baybal2 7y ago
> Lots of developers did not study CS at all I do feel the same. A lot of "computer science" degrees are in fact just basic programming ones, and that often goes to masters, and rare cases PhD level degrees. It is a common critic from industry that "computer science does not teach how to code," and I see too many universities seemingly taking it these days. It is ironic how once computing science was once a road to unemployability and coding was all rife, but now companies don't want to hire people without degrees to do menial jobs like webdev.
- Klathmon 7y ago
  Can we try to stop this gatekeeping and putting down some jobs as if they are "menial". A lot of the webdev work I've done has been significantly more challenging and technically difficult than most of the C work I've done. That's not to say C is "easier", it's not, but it is different. I've seen shitty devs in all areas, and I've worked menial jobs both in webdev and at the embedded C level (I had to write C code to display a custom font on a shitty LED display, that was easily the most boring job I've ever done).
  - vectorEQ 7y ago
    i don't do web stuff because it's horrible frustrating and difficult. C is nice, i love it as it matches the pc platform and you can debug it normally etc. A lot of people like to hate on 'frontent developers' or 'full stack javascript developers' or w/e but you are right. whatever floats your boat will be 'better' and 'more logical' than whatever sinks your ship. for me thank sinking is caused by scipring and CSS. for others that might be C.

ameyv 7y ago

This is really good resource.. Thank you

Jipazgqmnm 7y ago

https://www.nand2tetris.org/ https://www.nand2tetris.org/

eatonphil 7y ago

Going through a similar phase, though this is way further along. :) I had a great course in college on computer architecture that culminated in a processor in Logisim that could run fairly complex programs. (I recommend the Harris and Harris textbook for a surprisingly light/easy introduction [0].) But that was a while ago and I've never done anything for x86/amd64. I started working on an emulator [1] a few weeks ago but it interprets Intel x86 assembly rather than ELF files. I found this a great way to get started since parsing text is easier and the instructions you need to get a basic C program (compiled to assembly) running take an hour or two: call, push, pop, add. You can shim _start in without having to implement syscalls. Conditional jumping and syscalls took another weekend or two and now it can run some basic fibonacci C programs. I also had to build a graphical debugger for it to see what was going on... I will probably move to reading ELF files soon. I'll be writing up the process in a series on x86/amd64 emulator basics. [0] https://www.goodreads.com/book/show/2558730.Digital_Design_and_Computer_Architecture https://www.goodreads.com/book/show/2558730.Digital_Design_a... [1] https://github.com/eatonphil/x86e https://github.com/eatonphil/x86e

bogomipz 7y ago
Your emulator project is really neat. I would love to see more documentation on the design and process of it. The notes.md file was pretty spartan. Thanks for sharing. Cheers.
- eatonphil 7y ago
  Will post back once I start the series!
- eatonphil 7y ago
  Here's the first post: http://notes.eatonphil.com/emulator-basics-a-stack-and-register-machine.html http://notes.eatonphil.com/emulator-basics-a-stack-and-regis...
djhworld 7y ago
This is awesome, will look forward to following its progress

flanbiscuit 7y ago

Very cool! I had the same thoughts as you and bought "From Nand to Tetris"[1] a while ago but I did not get as far as you. You've inspired me to pick it back up and finish the book. Curious if you decided to use "But How Do It Know?" over "Nand to Tetris" for any specific reason or were you just not aware of the latter. 1. https://www.nand2tetris.org/ https://www.nand2tetris.org/

alpaca128 7y ago
Just a few days ago I found NandGame, which is a browser game where you build a computer starting with just the Nand gate and using only components you already built for the next one. Pretty cool idea.
djhworld 7y ago
Hi author here! I actually didn't set out on building anything, it all happened organically! I honestly cannot remember why I chose the book, I think I just saw the blurb and figured it was good enough to read. It was only when I was a couple of chapters in that I figured I could probably whip something up in code :)
- Hnrobert42 7y ago
  Hello author. I just wanted to heartily thank you for trying this and writing a post about it. I love seeing people pursuing technology for the sheer joy of it. Staring at the blank whiteness of an unwritten post, one wonders whether anyone else will notice or care what words will come tumbling out. But through your post, your work is multiplied. It is inspiring. So, again, thank you.
  - djhworld 7y ago
    No worries, thanks for the kind words. I got some great feedback from friends and colleagues before publishing it so thanks to them too :)
robbbbbbbbbbbb 7y ago
+1 for Nand to Tetris. As someone who came to computing through high level software and a little later than many (I wasn't dismantling appliances at age 5 like you hear in a lot of people's origin stories) this was a really empowering ground-up introduction to hardware architecture. One of the few Coursera courses [1] I actually finished and found rewarding, challenging and fun throughout. 1. https://www.coursera.org/learn/build-a-computer https://www.coursera.org/learn/build-a-computer

xigency 7y ago

> So I’m trying to get a better understanding of this stuff because I don’t know what L1/L2 caches are, I don’t know what pipelining means, I’m not entirely sure I understand the Meltdown and Spectre vulnerability papers. I wouldn't discourage anyone from learning about hardware from implementing gates or even looking at simple 8-bit CPUs, but if you are interested in learning how modern caches and pipelines work, there is a free Udacity course that goes into excellent detail [0]. You can also find the lecture videos on YouTube. This is originally an online course at Georgia Tech and the professor does an excellent job teaching these concepts. [0] https://www.udacity.com/course/high-performance-computer-architecture--ud007 https://www.udacity.com/course/high-performance-computer-arc...

dr_zoidberg 7y ago
There's a very good article [0] that makes rounds here very now and then. It gives a very good explanation of many of those concepts, while remaining understandable for those that haven't taken CPU design courses. [0] http://www.lighterra.com/papers/modernmicroprocessors/ http://www.lighterra.com/papers/modernmicroprocessors/ Edit: It'd be great a 2019 refresh (last update is from 2016) talking about Ryzen and the newer Intel designs.
- djhworld 7y ago
  Bookmarked, thanks for the link, I think it will help me with the next step
taormina 7y ago
I took this class at Georgia Tech as an undergrad and I also highly recommend it for the material. We had a chain of CS classes leading up to it (2110 -> 2200 -> 4290) on the undergrad side, but when I took it, this course was actually cross-listed as both an undergrad and graduate CS and ECE class (so CS 4290/6290 and the same sort of thing for the ECE major were all in the same literal lecture hall). Of course, most CS students were only taking this if they were in the System & Architectures thread (or maybe Devices?), but most CS students had to at least take up to CS 2200 (Systems & Networks, which basically took the concepts up to "Build me a working 1 CPU computer", whereas this class took the next steps from "Okay, so how do we do better than 1 instruction per cycle?"). Multi-core processors are really cool! I frequently take for granted that most people don't have this foundational knowledge. The basics come up more than you'd think, especially when provisioning the right hardware for the task.

js2 7y ago

> However, after making my way through But How Do It Know? by J. Clark Scott, a book which describes the bits of a simple 8-bit computer from the NAND gates, through to the registers, RAM, bits of the CPU, ALU and I/O, I got a hankering to implement it in code. Speaking of code, another excellent book along these lines is Code: The Hidden Language of Computer Hardware and Software by Charles Petzold. http://www.charlespetzold.com/code/ http://www.charlespetzold.com/code/

heinrichhartman 7y ago
yes, that's notably the only publication by Microsoft Press, I can recommend ;)
- segfaultbuserr 7y ago
  > the only publication by Microsoft Press Really? https://www.microsoftpressstore.com/store/browse/programming https://www.microsoftpressstore.com/store/browse/programming
  - C4stor 7y ago
    Odds are the last comma is a typo ^^
    - segfaultbuserr 7y ago
      Aha, I see what you meant. Quite interesting to see how ambiguity can be created by a mere comma in real life.
      - deleted 7y ago
        [deleted]
- Insanity 7y ago
  I'm pretty sure Code Complete2 is a publication by Microsoft Press. I'd say that's a pretty well known and well worth reading book.

tamaharbor 7y ago

“See all that stuff in there, Homer? That’s why your robot never worked.” - Marge Simpson

pjc50 7y ago

> https://github.com/djhworld/simple-computer/blob/master/cpu/cpu.go#L763 https://github.com/djhworld/simple-computer/blob/master/cpu/... The author themselves points out that a "big pile of gates" is not the best approach here, but I'm kind of surprised that at no point did they attempt to build another representation of the circuit and either execute it in a table-driven way, or write a short script that spits out go for compilation.

gnode 7y ago
> but I'm kind of surprised that at no point did they attempt to build another Perhaps because the existing implementation had already served its purpose - an educational exercise to understand CPU design, and not an instruction-level emulator or transcompiler.
djhworld 7y ago
Thanks for the feedback, these are some good ideas if I was do do this again. I'm sorry you didn't think I took the best approach.

thrower123 7y ago

I still think the single best course I took in college was my computer architecture course. We built an entire 8-bit CPU up from individual gates over the course of the semester in Logisim[1], to the point where we could compile a limited version of C down to the machine code for our simulated processor and load it into the simulated main memory and run it. I'm incredibly glad there was that hands-on component to the course, rather than just the theoretical textbook and lectures learning; it was hard as hell, and I actually ended up dropping it the first time and taking it again later, but at the end I actually felt like I kinda knew what was going on. Pointers were never mysterious again, at least. [1] http://www.cburch.com/logisim/ http://www.cburch.com/logisim/

blago 7y ago

I took an architecture class back in college and the first time we met, the professor gave us a couple of programs described in plain English. One of them was basically sorting, and the other one something else. Each of us spent the rest of the semester picking an instruction set, designing a system, writing an emulator, and writing the code that would perform the tasks described on the first day. I went a little overboard and created a C backend for the emulator along with an in-browser JS client that was pretty much a full-blown machine language IDE and debugger. Needless to say, this feature creep didn't end well. I barely made it work well enough to get an ok grade but I learned that overconfidence can be more dangerous than the lack of. Here's what I was able to salvage from the front end on short notice: http://blago.dachev.com/~blago/CS-535/stage_2/src/web/ http://blago.dachev.com/~blago/CS-535/stage_2/src/web/ It's using ext.js which was pretty cool at the time.

Hendrikto 7y ago
> I barely made it work well enough to get an ok grade but I learned that overconfidence can be more dangerous than the lack of. That is a very important lesson.
- w0utert 7y ago
  Yeah, reminds me of the time I had to write a BSP tree builder as a course assignment, and ending up spending 2 months writing an OpenGL renderer + an importer for the Apple QuickDraw 3D API instead (hint: don't try to do that, it's almost a full object-oriented programming language in itself if you want to support even a moderately complex model). All just because I found some nice architecture models that were only available in QD3D format, and I was convinced it would only take me a few hours to read them... I only got the brilliant idea of just converting them to something simpler like .3DS after I already finished the assignment >_<
lioeters 7y ago
> I went a little overboard and created a C backend for the emulator along with an in-browser JS client that was pretty much a full-blown machine language IDE and debugger. Haha, this made me smile. I can totally relate to that ambitious line of thinking: given a task to solve, you imagined the logical next steps, to build an environment for solving that general class of tasks. Great lesson about feature creep, but I also think that kind of vision and ambitious problem-solving can be valuable in the long term, if it works the whole community/ecosystem can benefit.

gilbetron 7y ago

(Way) back in college, we had been learning high-level programming concepts (UI, OS, Compilers, Algorithms, etc), underlying math behind computing, and physics up through circuits. My favorite course was Computer Architecture which was set up to pull everything together, mostly through a series of simulated computer projects, until, at the end, you realized you knew how a computer worked from math, through physics, and up to what the person interacted with. One of my favorite educational experiences ever. The Professor (Yale Patt) was a really interesting guy, great storyteller, and still actively worked with Intel. I also thought he was really friendly, turns out he just liked talking my girlfriend at the time and I was a tag-along ;)

sanderjd 7y ago
This was my favorite part of college too. I think it was near the end of a really good networking class I took maybe my junior year when I distinctly remember chatting on AIM and thinking about how I could visualize approximately how my key presses were going from the hardware through the OS into memory into instructions on the CPU executing the application back out onto my screen and across the network to a server and on to my friend's machine for the reverse trip. It was a powerful moment. Of course as I've gone further through my career I've realized how far off my approximation was because everything is even more complex in the details, but I still think it was a fundamentally valid and valuable moment. This is one reason I'm ambivalent about the skepticism around computer science / engineering programs as a prerequisite for a career in software development. It bums me out to think of people toiling at this work without experiencing that kind of bottom-up knowledge of computing. But I think this is largely a projection of my own personality on others; that would be a bummer for me, but I think many people don't care about any of that and just want to do valuable work for good pay.
elamje 7y ago
Glad to hear from another survivor of Dr. Patts class. I took him for intro to computing first semester of college with no programming experience and I got wrecked by his class, but most of the content has stuck with me up through my career!

levelist_com 7y ago

Check out the following: The Elements of Computing Systems: Building a Modern Computer from First Principles https://www.amazon.com/Elements-Computing-Systems-Building-Principles-dp-0262640686/dp/0262640686/ref=mt_paperback https://www.amazon.com/Elements-Computing-Systems-Building-P...

ixtli 7y ago

I took a computer architecture course in undergrad and they had us make an ARM emulator similar to this in c++. It was extremely illuminating.

djhworld 7y ago
Cool. I always find that "learn by doing" works best in these sorts of things :)

balls187 7y ago

The final for Computer Architeture had us building an 8-bit CPU. It was a multiweek project, starting with designing the instruction set leading up to building the CPU in software implementing bubble sort in assembly. The first and only time I had to do an all nighter (2 actually) in college was due to that project. Two days before the final presentation, the CPU didn't work. After a few clock cycles the memory would contain garbage. I ended up rebuilding it from scratch debugging every step of the way only to find out the 1-bit mux (a primitive supplied with the software) was wired backwards. 0 corresponded to the B input, and 1 selected the A input. Once I correct that, the CPU worked like a charm, we nailed the final preso, and I slept for 16 hours.

cobookman 7y ago
Had to do the same assignment. I highly recommend doing it. Was the most painful thing I ever did in college, but it taught me so much about how processors work, and how to code in C.
- _han 7y ago
  Is there a public resource somewhere that describes the assignment/gives some guidelines? I would like to give it a try.
  - cweagans 7y ago
    https://www.nand2tetris.org/ https://www.nand2tetris.org/ goes through the same process. Highly recommend!
    - BanazirGalbasi 7y ago
      The game MHRD (MicroHard) offers the same content, but in an interactive environment. I haven't gone much into it yet so I don't know how the end content compares to Nand2Tetris, but a lot of people say they're different methods of teaching almost identical content.

blattimwind 7y ago

> I don't know how CPUs work Guess introductory courses in universities aren't useless after all.

russellbeattie 7y ago

Ben Eater has a series of videos where he builds an 8 bit computer using actual chips. He starts from first principals and it's pretty amazing to see it come together. Definitely worth watching. Building an 8-bit breadboard computer!: https://www.youtube.com/playlist?list=PLowKtXNTBypGqImE405J2565dvjafglHU https://www.youtube.com/playlist?list=PLowKtXNTBypGqImE405J2...

lqet 7y ago

Nice work. Somewhat related to the Megaprocessor by James Newman [0] [0] http://www.megaprocessor.com/progress.html http://www.megaprocessor.com/progress.html

djhworld 7y ago
I watched the Computerphile episode about this on Youtube when I was in the midst of the project, apparently it's at a Computer History museum in Cambridge now, I really should find the time to go!

afpx 7y ago

This is very cool. It would be so fun to run qemu on it. https://www.qemu.org/ https://www.qemu.org/.

djhworld 7y ago
I think the machine would need to be much _much_ faster, with the stack pointer register + a few extra instructions to even attempt a project like that hahahahaha

Zrdr 7y ago

Congrats ! This reminds me of this amazing computer done in the cellular automaton Wireworld. https://www.quinapalus.com/wi-index.html https://www.quinapalus.com/wi-index.html

vectorEQ 7y ago

cool project and nice writing style on the blog. awsome!

hawkjo 7y ago

Quick shout out to NAND Game, a version of this laid out as a computer game. Delightful, free, web-based. http://nandgame.com/ http://nandgame.com/

hathawsh 7y ago
That is awesome. I plan to challenge my kids to finish that game this summer.

anderspitman 7y ago

I went back to school for CS after 6 years of professional programming. Just for being guided through logic gates, assembly, and implementing a simple CPU in an FPGA I consider it well worth the time and money. The point when I realized I finally understood (on a surface level) everything from the electrical signals to my JavaScript reminds me of when I finished the last video of Khan Academy's series on Euler's formula and "understood" it, if only for a moment.

arcticbull 7y ago

I did this too, when I was in college. I implemented a gameboy CPU emulator. Then I wanted to know how FPGAs work so I implemented a Chip-8 CPU on an FPGA. Once I clean it up, I'll throw it up on my GitHub and maybe write up a quick medium post. This is exactly how I learn: I don't know how something works, so I make one.

djhworld 7y ago
> This is exactly how I learn: I don't know how something works, so I make one. Uh huh, the FPGA Chip-8 thing sounds awesome! Definitely post about it!
bogomipz 7y ago
Please do, this would be an interesting read. Cheers.

mar77i 7y ago

I got this link yesterday or so. I breezed through it until the memory latch: http://nandgame.com/ http://nandgame.com/

djmips 7y ago
Try this! It's fun!
rdc12 7y ago
Did you manage to make the latch in the end? I would imagine feedback would be a tricky subject to try learn without help.

nlowell 7y ago

Implementing a CPU simulation is a classic college exercise, as you can see in these comments. Super valuable based on how memorable it was for everyone! It really helps de-mystify computers.

peter303 7y ago

Thats how Gates and Allen wrote their BASIC interpreter for the Altair microcomputer and started MicroSoft. They did not have access to a working 8080 microcomputer so they simulated one on a Harvard mainframe from a machine language specification. Bill took the interpreter by punch tape to MITS in Albuquerque. And legend has it their BASIC worked only after an hour of fiddling.

djhworld 7y ago
That's such a cool story haha. Not sure if my thing is remotely close to that, but nice to know I'm standing on the shoulder of giants :)

floor_ 7y ago

Making a chip-8 emulator is a reasonable project for those who are interested.

merlincorey 7y ago
I'm in the final stretches of mine right now, in fact. The article describes an 8 bit CPU with 17 instructions. CHIP-8 is an 8 bit CPU with 31 instructions, but crucially, it has a large amount of documentation[0] and a nice corpus of ROMS available[1] making it a bit easier as you don't have necessarily write your own programs for a CPU you don't fully understand yet. [0] See http://devernay.free.fr/hacks/chip8/C8TECH10.HTM http://devernay.free.fr/hacks/chip8/C8TECH10.HTM among many other resources [1] For example this archive of the now defunct chip8 archive site https://github.com/dmatlack/chip8/tree/master/roms https://github.com/dmatlack/chip8/tree/master/roms
- djhworld 7y ago
  Just looking at the docs, those 31 instructions would definitely help a lot, along with the stack pointer register. I'd definitely recommend doing something like that (not at the logic gate level though - too slow) but an emulator is a fun project to tackle. I wrote my Gameboy emulator first which is a bit more complicated than chip-8 and at the time the documentation was a lot more varied.

ibeckermayer 7y ago

I'm working on a similar project, implementing the architecture described in this book (https://www.nand2tetris.org https://www.nand2tetris.org). Ultimately I hope to implement it on an FPGA with attached keyboard and screen and actually use it to compute stuff: https://github.com/ibeckermayer/Nand2TetrisFPGA https://github.com/ibeckermayer/Nand2TetrisFPGA

djhworld 7y ago
Will look forward to following its progress!
- ibeckermayer 7y ago
  Thank you :)
mikevin 7y ago
Nice project. I've finished most of the course (up until the compiler because that's where it became too familiar) and I'm now redoing it on an actual fpga. It's a great learning experience and I can fully recommend keeping at it, it's one of the most rewarding projects I've done. Actually bought a Pynq Z2 last week to have some peripherals to connect and to drive it easily. Might put it up github too.
- ibeckermayer 7y ago
  Nice. I looked around online and it seems like others have attempted something like this but I didn't find any project that looked complete. I have a Basys 3 board which has VGA and USB I/O, so I hope to actually get from Nand to actually playing Tetris on my homespun platform.

sehugg 7y ago

Shameless plug -- hardware engineering students are using the online 8bitworkshop IDE to study and design custom CPUs in Verilog: https://8bitworkshop.com/redir.html?platform=verilog https://8bitworkshop.com/redir.html?platform=verilog

elamje 7y ago

Any Yale Patt alums here?

kickopotomus 7y ago
EE360N Labs all over again. Tangentially, does anyone know what Patt has had to say about Meltdown/Spectre? Speculative execution was/is his bread-and-butter if I remember correctly.
GrumpyYoungMan 7y ago
Giant beard? Fond of telling people that one of his grad students was the chief architect of the Pentium III? Yeah, I remember his comp. arch. classes fondly.

dustfinger 7y ago

People who are interested in building their own computer might enjoy the Bitwise [1] project over at the Handmade Network. [1]https://bitwise.handmade.network/ https://bitwise.handmade.network/

nstart 7y ago

As a layman on this topic, I'm curious about the difficulty around this project: It seems like a lot of people have gone through similar experiences of building an 8 bit CPU simulator/emulator. Curious why it's not 64 bits. I can guess the answer is "it's hard". I'm just wondering where the difficulty lies. Is it in the standards? The mechanical feasibility of connections? Actual limitations of building a 64 bit emulator on a machine powered by a 64 bit processor? Apologies if the question seems obvious. I come into this knowing next to nothing and I could probably find the answer with some research of my own. Just wanted to ask the community for thoughts here ️

dpe82 7y ago
Designing a simple 64 bit CPU is not really more work than a simple 8 bit processor. 64 bit CPUs tend to have more features than just wider registers though.
djhworld 7y ago
For this project? It wouldn't have been difficult to upgrade the machine to 64-bit, it's really just a matter of increasing the bus width and register size. But it would slow it down massively due to me writing it in a general purpose programming language and passing around booleans everywhere, there's a lot of for loops that copy things in and out of buses and I would have to increase the size of the ALU to accomodate the bigger numbers.

madrox 7y ago

Reminds me of the early days of unmodded Minecraft when someone made a CPU in game with lots and lots of redstone. It really makes otherwise arcane concepts accessible. Super cool!

DonHopkins 7y ago

I love how you can actually see the different parts of Guy Steel's Lisp Microprocessor, which he designed in Lynn Conway's legendary 1978 VLSI System Design Course at MIT. http://ai.eecs.umich.edu/people/conway/VLSI/MIT78/MIT78.html http://ai.eecs.umich.edu/people/conway/VLSI/MIT78/MIT78.html The Great Quux's Lisp Microprocessor is the big one on the left of the second image, and you can see his name "(C) 1978 GUY L STEELE JR" if you zoom in: "Guy Steele: LISP microprocessor (LISP expression evaluator and associated memory manager; operates directly on LISP expressions stored in memory)." http://ai.eecs.umich.edu/people/conway/VLSI/InstGuide/MIT78chip%20photo-2%20L.jpg http://ai.eecs.umich.edu/people/conway/VLSI/InstGuide/MIT78c... And here is a map of the different parts of the Lisp microprocessor: https://imgur.com/zwaJMQC https://imgur.com/zwaJMQC Here is the chalk board where they kept track of all the student's projects and where they would go on the chip: http://ai.eecs.umich.edu/people/conway/VLSI/MIT78/Status%20Em.jpg http://ai.eecs.umich.edu/people/conway/VLSI/MIT78/Status%20E... And the layout of the chip with everyone's project (with the big Lisp microprocessor standing out at the lower left): "The final sanity check before maskmaking: A wall-sized overall check plot made at Xerox PARC from Arpanet-transmitted design files, showing the student design projects merged into multiproject chip set." http://ai.eecs.umich.edu/people/conway/VLSI/MIT78/Checkplot%20s.jpg http://ai.eecs.umich.edu/people/conway/VLSI/MIT78/Checkplot%... This is a photo of one of the wafers they made, with lots of chips: "One of the wafers just off the HP fab line containing the MIT'78 VLSI design projects: Wafers were then diced into chips, and the chips packaged and wire bonded to specific projects, which were then tested back at M.I.T." http://ai.eecs.umich.edu/people/conway/VLSI/MIT78/Wafer%20s.jpg http://ai.eecs.umich.edu/people/conway/VLSI/MIT78/Wafer%20s.... And here the classic paper about it, "Design of a LISP-based microprocessor" by Guy Lewis Steele, Jr. and Gerald Jay Sussman: https://dl.acm.org/citation.cfm?id=359031 https://dl.acm.org/citation.cfm?id=359031

ZedIsNotDead 7y ago

Modern problems require modern solutions.

cptnapalm 7y ago

You can also do this with UNIX pipes and a few small C programs, apparently. https://www.linusakesson.net/programming/pipelogic/index.php https://www.linusakesson.net/programming/pipelogic/index.php