I don't know how CPUs work so I simulated one in code (2019)
1–10 of 49 posts
Re: I don't know how CPUs work so I simulated one in code (2019)
#2Neat, I've seen a few logsim systems. After watching Ben Eaters videos (and not having enough time to tinker with hardware) I built
Re: I don't know how CPUs work so I simulated one in code (2019)
#3Discussed at the time:
I don't know how CPUs work so I simulated one in code - https://news.ycombinator.com/item?id=19969321 - May 2019 (172 comments)
Re: I don't know how CPUs work so I simulated one in code (2019)
#4So, what this project misses, which is quite hard to capture if you think of gates being just on off switches, is the fact that signals are not instantaneous, and everything runs in parallel.
As the AND gate 4 gates up the chain switches the NOT gate 4 gates down the chain starts to send different and unstable signals which may or may not be interpreted as a 1 or 0 in the downstream gate.
That's the reason computers have a clock, to make sure all transistors in a given stage of a CPU reach a steady state before moving on to the next instruction.
This is why it's probably a good idea to work with a HDL instead of just trying to wing it.
Re: I don't know how CPUs work so I simulated one in code (2019)
#5If, for fun, I wanted to train an ML model on a ton of CPU instructions (which each predicted state/label being the state of the registers), does anyone have any clue how to gather that kind of data?
Re: I don't know how CPUs work so I simulated one in code (2019)
#6If, for fun, I wanted to train an ML model on a ton of CPU instructions (which each predicted state/label being the state of the registers), does anyone have any clue how to gather that kind of data?
Maybe a game console emulator?
Re: I don't know how CPUs work so I simulated one in code (2019)
#7Reminds me of some scenes from the first book of the three body problem.
Re: I don't know how CPUs work so I simulated one in code (2019)
#8So, what this project misses, which is quite hard to capture if you think of gates being just on off switches, is the fact that signals are not instantaneous, and everything runs in parallel. As the AND gate 4 gates up the chain switches the NOT gate 4 gates down the chain starts to send different and unstable signals which may or may not be interpreted as a 1 or 0 in the downstream gate. That's the reason computers…
The game Silicon Zeroes ( https://store.steampowered.com/app/684270/Silicon_Zeroes/ ) teaches this. It starts out with components computing their outputs instantaneously, but then introduces the concept of microticks such that the output of a component is unstable until its inputs are stable enough for some time, so the clock speed must be adjusted according to the largest delay in all circuit paths. The game starts off with simple circuits but very quickly becomes about making a CPU, although the ISA is hard-coded into the game and very small.
Another game Turing Complete ( https://store.steampowered.com/app/1444480/Turing_Complete/ , https://news.ycombinator.com/item?id=38925307 ) lets you build a CPU from basic gates and a much larger (and customizable) instruction set. It also has the concept of gate delays, thopugh it doesn't visually show the unstable output as Silicon Zeroes does.
Re: I don't know how CPUs work so I simulated one in code (2019)
#9So, what this project misses, which is quite hard to capture if you think of gates being just on off switches, is the fact that signals are not instantaneous, and everything runs in parallel. As the AND gate 4 gates up the chain switches the NOT gate 4 gates down the chain starts to send different and unstable signals which may or may not be interpreted as a 1 or 0 in the downstream gate. That's the reason computers…
Propagation delay, besides being physically unavoidable, is actually necessary for things like latches (and thus memory) to work, since they rely on feedback loops. The https://en.wikipedia.org/wiki/Ring_oscillator is another example.
Re: I don't know how CPUs work so I simulated one in code (2019)
#10I was once shown a dos-based CPU simulator back in the mid/late 90s.
From memory it showed instruction decode, execution, cache and memory.
Unfortunately I've never been able to find it, because all the google results are about running DOS games and/or DOSBox.