Simple CPU Design • Hacker News Board

Re: Simple CPU Design

#41

Post by Cogito » Thu, Jan 23, 2025, 6:07 AM UTC

For those who haven't seen it before, throwing out nand2tetris and nandgame as another interesting journey from logic gates -> computer programs running on a CPU.

nandgame, in particular, is really easy to get started with and has been updated quite a lot over the year. If you looked at it a while ago check for new updates!

nand2tetris goes into a bit more detail around some things, I like it too but harder to get started with.

https://www.nand2tetris.org/

https://www.nandgame.com/

Re: Simple CPU Design

#42

Post by joshu » Thu, Jan 23, 2025, 8:10 AM UTC

phendrenad2 wrote: post #39

cjfd wrote: post #9

I considered trying to do a simple CPU design from logic gates too. But I ended up wondering about some of the performance characteristics. Maybe some people who are knowledgeable are reading this. What I am wondering about is the switching speed of logic gates as compared to the signal speed in the electric connections for a realistic CPU. I.e., how many logic gate lengths (assume logic gates to be square) does an e…

The performance characteristics won't be great, but it would still be a fun project. In fact one of the early 32-bit RISC processors, PA-RISC, was originally shipped as a set of four large boards covered in discrete 74-series logic. Which actually includes a large ALU chip (without which the design would probably span 8 boards instead...)

The pa-risc ts1, more here https://www.openpa.net/pa-risc_processor_pa-early.html and https://computermuseum.informatik.uni-stuttgart.de/dev_en/hp...

Re: Simple CPU Design

#43

Post by adornKey » Thu, Jan 23, 2025, 12:58 PM UTC

Cogito wrote: post #41

For those who haven't seen it before, throwing out nand2tetris and nandgame as another interesting journey from logic gates -> computer programs running on a CPU. nandgame, in particular, is really easy to get started with and has been updated quite a lot over the year. If you looked at it a while ago check for new updates! nand2tetris goes into a bit more detail around some things, I like it too but harder to get st…

Another game like this is TuringComplete. It's not free, but even more comfortable. https://turingcomplete.game/

Re: Simple CPU Design

#44

Post by h3half » Thu, Jan 23, 2025, 1:31 PM UTC

adornKey wrote: post #43

Cogito wrote: post #41

For those who haven't seen it before, throwing out nand2tetris and nandgame as another interesting journey from logic gates -> computer programs running on a CPU. nandgame, in particular, is really easy to get started with and has been updated quite a lot over the year. If you looked at it a while ago check for new updates! nand2tetris goes into a bit more detail around some things, I like it too but harder to get st…

Another game like this is TuringComplete. It's not free, but even more comfortable. https://turingcomplete.game/

I can highly recommend TuringComplete. If you know what you're doing the start can feel a little hand-holdy, but by the end of the game you have a functioning computer running an assembly language of your design and it's fairly close to an open sandbox.

Building up to that point having started from the basics was very neat

Re: Simple CPU Design

#45

Post by apricot » Thu, Jan 23, 2025, 2:11 PM UTC

ofrzeta wrote: post #11

cjfd wrote: post #9

I considered trying to do a simple CPU design from logic gates too. But I ended up wondering about some of the performance characteristics. Maybe some people who are knowledgeable are reading this. What I am wondering about is the switching speed of logic gates as compared to the signal speed in the electric connections for a realistic CPU. I.e., how many logic gate lengths (assume logic gates to be square) does an e…

does this answer your question? https://monster6502.com/ "The MOnSter 6502 runs at about 1/20th the speed of the original, thanks to the much larger capacitance of the design. The maximum reliable clock rate is around 50 kHz. The primary limit to the clock speed is the gate capacitance of the MOSFETs that we are using, which is much larger than the capacitance of the MOSFETs on an original 6502 die."

"We are working towards a public launch, currently planned for Mid 2023"

Hmmm...

Re: Simple CPU Design

#46

Post by jecel » Thu, Jan 23, 2025, 4:20 PM UTC

avmich wrote: post #22

A nice non-Turing-tarpit minimalistic MCPU: https://github.com/cpldcpu/MCPU .

Just expanding it from 8 to 16 bits makes it practical, if still awkward. I implemented the 2048 game on that, for example.

https://github.com/jeceljr/digitalCPUzoo/tree/main/MCPU

Re: Simple CPU Design

#47

Post by nayuki » Thu, Jan 23, 2025, 4:45 PM UTC

Related - breadboarding and computer engineering tutorials: https://www.youtube.com/@BenEater/videos

Re: Simple CPU Design

#48

Post by zamadatix » Thu, Jan 23, 2025, 5:44 PM UTC

JLCarveth wrote: post #34

helij wrote: post #24

I just have to say. Such a beautiful and accessible website. No fluff, no ads, no distractions. I love it!

No HTTPS either

It does have HTTPS, just with a self signed cert. No auto-redirect though.

Re: Simple CPU Design

#49

Post by imtringued » Thu, Jan 23, 2025, 6:52 PM UTC

cjfd wrote: post #9

I considered trying to do a simple CPU design from logic gates too. But I ended up wondering about some of the performance characteristics. Maybe some people who are knowledgeable are reading this. What I am wondering about is the switching speed of logic gates as compared to the signal speed in the electric connections for a realistic CPU. I.e., how many logic gate lengths (assume logic gates to be square) does an e…

I'm just here to point out that your question is nonsensical. You're asking for propagation delay of the wires vs switching time of the gates, but you don't want the propagation delay to be measured by the time it takes for a signal to be propagated or the switching time of the not gate, so you are instead asking the total propagation delay to be normalized by the switching time of a not gate and somehow calculate that back into a wire length equivalent normalized by the longest dimension of a not gate.

None of these things make much sense.

Also as an approximate answer to your question: The simplest circuit without a flip flop aka an oscillator can easily reach hundreds of GHz using silicon germanium based semiconductor manufacturing

Re: Simple CPU Design

#50

Post by garaetjjte » Thu, Jan 23, 2025, 7:07 PM UTC

I'm pondering about building CPU from logic gate chips. The thing is most projects like that use chip count efficient (usually microcoded) designs which aren't fast enough to run "real" familiar software. I want 32-bit instruction set with virtual memory, capable of running Linux and fast enough to run games like Doom. Fastest reasonably available logic gate family is 74AUC (possibly with exception of exotic ECL gates). Combined with copious use of fast asynchronous SRAM chips, I think performance in the ballpark of 20 MIPS should be attainable. I'm half-expecting that I'm making some huge error in my assumptions and it will turn out these numbers are impossible, but that didn't happen yet.