I don't know how CPUs work so I simulated one in code (2019)
The author simulated an 8-bit CPU to understand computer architecture, learning about bits, ALU functions, and I/O communication, while planning to explore advanced topics like RISC architectures and modern CPU features.
Read original articleThe author reflects on their journey to understand how CPUs work by simulating a simple 8-bit computer in code, inspired by the book "But How Do It Know?" by J. Clark Scott. Despite lacking a deep understanding of modern computing concepts, the author embarked on this project to grasp the fundamentals of computer architecture. They implemented a basic CPU that can execute simple programs, handle keyboard inputs, and render text on a display. The simulation involved creating a crude assembler and managing limited registers without a stack pointer or interrupts, which presented challenges. Through this process, the author learned about the movement of bits, the function of an ALU, and the basics of I/O communication. They also recognized the complexity behind writing assembly code and the effort required to develop even simple applications. The project was rewarding, enhancing their appreciation for computer systems and motivating them to explore more advanced topics, including RISC architectures and modern CPU features like caches. The author acknowledges that while this knowledge may not be essential for their day job, the learning experience has been enjoyable and fulfilling.
- The author simulated a simple 8-bit CPU to better understand computer architecture.
- The project involved creating a basic assembler and managing limited registers.
- Key learnings included the movement of bits, ALU functions, and I/O communication.
- The author plans to explore more advanced topics like RISC architectures and modern CPU features.
- The experience enhanced their appreciation for the complexity of computer systems.
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- Several commenters have undertaken similar projects, highlighting the challenges and time investment involved.
- There is a recognition of the complexities of CPU design, including the importance of timing and signal stability.
- Many participants reference educational experiences or resources, such as courses or YouTube channels, that have influenced their understanding of computer architecture.
- Some comments suggest alternative methods for CPU interaction, such as using UART for communication.
- Overall, the community expresses a strong interest in exploring and discussing CPU simulation and design.
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.
I don't know how CPUs work so I simulated one in code - https://news.ycombinator.com/item?id=19969321 - May 2019 (172 comments)
His channel has a lot of other really great stuff on general electronics as well.
I built a simple 8-bit computer using a Z80 chip. You can read about it a bit more here https://www.jake-reich.co.uk/zx-jakey
I just recently wrote a JavaScript emulator [1] for a simple 8-bit CPU I had built with logic gates. Both were fun projects, but one took a weekend whereas the other took about 4 months. Having skimmed through the author's code, I totally understand why it took them so much longer to get their's working. It's implemented with gate-level simulated logic gates, which is an impressive achievement. It's so much easier to just emulate whole components like I did.
[1] https://naberhausj.com/miscellaneous/8-bit-computer/page.htm...
What I learned from Ben Eater is that a non-cheaty solution would have been to write a simple UART serial "device" and then interacted with the CPU via serial communication with a terminal.
CPU just happens to be one of them. Fascinating that such a seemingly complex marvel of innovation is just something that everyone can do.
Of course, there's lots of groundwork and you need to know "the trick" (eg. that you can use transistors to make computation machines)... but it's easily within your grasp.
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.
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