by dreamcompiler
1 subcomments
- "This makes the machine transparent in a way that microcode-based designs cannot be."
Every output bit m of microcode can be equivalently expressed as a logic function of n inputs where the microcode has n incoming address lines. This no less transparent than pure logic if you know the contents of the microcode. Microcode is often preferred because changing it is much easier than changing a bunch of gate logic. IMHO factoring your design into registers vs. control signals and putting the control signals into microcode makes the design more transparent than having a giant sea of gates.
by gabrielsroka
1 subcomments
- Ben Eater's SAP came from "Digital Computer Electronics" by Albert Paul Malvino and Jerald A. Brown
https://en.wikipedia.org/wiki/Simple-As-Possible_computer
by osigurdson
1 subcomments
- A 2nd year project back in the day was to build a 4 bit CPU on a breadboard. We had the advantage of having an ALU IC but was still quite tough to get working!
by loloquwowndueo
3 subcomments
- So this was all just simulated? Where are the pictures of the build?
Back in the day i built a 4-bit CPU on a breadboard (it was huge actually spanned 3 breadboards). Programming the ROM by hand like cavemen (to be fair it was the cave ages). We didn’t carry cameras in our pockets so sadly we didn’t get a picture.
- This is also very well documented. Probably as part of the assessment, but it's nice to see.
It doesn't appear to have any kind of interrupts, which is quite a limitation for actual usecases, but also makes the architecture much simpler.
The use of dual phase clocking is interesting. The document describes it as having the control and data paths operating on opposite phases. I'm curious as to where you got this technique from, since it's not common (apart from the use of both edges by DDR RAM). I also suspect that it would go away if you had better tooling for managing setup and hold violations (does logisim do that for you, or did you have to manage it manually somehow?). Not all FPGA tools like nonstandard clock architectures.
- Awesome project, re fpga implementation one option you might want to explore are used Bitcoin miner control boards if you want the best logic units/$ ratio. I've used the EBAZ4205 (zynq 7010) control boards with a cheap/generic FT2232HL dev board and it works great. Of course it's a bit more of a pain compared to a regular dev board
- Very nice. I wonder if implementing a one-instruction set computer (for example something that implements Adrian Cable's subleq VM, see https://www.ioccc.org/2025/cable/) would be educational and whether it can make the design of a computer from discrete logic chips simpler or more complex. Though it would very likely not be as efficient.
- I did something similar for a school capstone project. It brings back memories. Writing Verilog, working with FPGAs, that sort of thing. But this goes even further and actually gets into hardwired implementation, which is really impressive. Actually, using if else statements just creates MUXes, so you don't have fanout issues to worry about. But for something like this, you would have to handle timing calculations for rising and falling edges. It is really remarkable.
- the rom-to-ram bootstrap is a nice touch. after it hands over, what stops
the bootloader from writing to I-SRAM again? a mode flag in the control matrix?
- Computer architecture (I think my uni named it comp org) was one of my toughest courses in undergrad! It steered me away from hardware. I now wonder if that is still the case today? ARM has exploded onto he scene and I'm fascinated by the sheer amount of development going on in the chip space.
by throwaway2016a
0 subcomment
- I hd to do a 4-bit version of this back in 2006 for my Computer Science undergrad. Interesting to see EE students doing it as well. Like many people here, we had to build it on actual breadboards. Which I think adds a ton to the experience.
by sarmadgulzar
1 subcomments
- Are you from Pakistan? I have an Alchitry Cu FPGA board for my personal use if you want to borrow it for implementation. Awesome project btw!
by alfienightshift
0 subcomment
- Nice developments, keep going
by chrisakoury
1 subcomments
- Logisim was the shit back in Uni
Very implressive tbh
You should include a screenshot of the logisim diagram
- amazing 2nd year i was playing starcraft all day
by bcjdjsndon
0 subcomment
- That ipc lol were all 8bit CPUs less than1 instruction per cycle?
by HerbManic
2 subcomments
- With all the talk about developers being lazy and younger folk not understanding the technology they use, it is always great to see examples of core foundational work still being done. Makes the rest of that talk feel like fear mongering.
by andrewvu0203
0 subcomment
- [flagged]
- [dead]
by rahadbhuiya
0 subcomment
- [dead]
- Neat!
Now do it the other way round and make the 8 bit cpus become a 2nd year EE student.
by assimpleaspossi
1 subcomments
- >>me and my friends ...
My friends and I...