5 ms·

16-bit Serial Homebrew CPU

137 points by freedude 3y ago

heikkilevanto 3y ago
Looks like the site could not handle the traffic. https://web.archive.org/web/20230820212723/www.jiristepanovsky.cz/project.php?p=23cpu https://web.archive.org/web/20230820212723/www.jiristepanovs...
nickt 3y ago
If you don’t make it to the end of the article you may not see the massive rabbit hole down there that is the https://www.homebrewcpuring.org/ https://www.homebrewcpuring.org/ - some incredible projects there, I had no idea this was so popular!
- artemonster 3y ago
  I think this ring is 75% responsible for my choice of profession (HW Eng that designs CPUs) :)
  - boesboes 3y ago
    I wish I ran into this 20 years ago, I got into the whole web application development business and now I’m stuck dreaming of transistors ;)
    - z500 3y ago
      I've been dreaming of transistors since I got a kit for some electronics projects as a kid, but after frying a few components I also went on to web applications. I designed a CPU in Logisim after watching Ben Eater's videos, but I don't know if I have it in me to turn it into a physical thing. I'd love to get one onto an FPGA, or if I won the lottery some day, have one fabricated.
- ddingus 3y ago
  Wow! No kidding!
wglb 3y ago
This is very impressive. It reminds me of David Conroy's FPGA emulation of the DEC alpha: http://fpgaretrocomputing.org/ http://fpgaretrocomputing.org/
emeraldd 3y ago
Home brew computers! The Magic-1 was one of my favorites to read about .. http://www.homebrewcpu.com/index.htm http://www.homebrewcpu.com/index.htm
userbinator 3y ago
Depending on where you place the line between a state machine and a CPU, my 16-bit system might actually be the CPU with the lowest amount of ICs. Comparisons like this have always seemed a bit unnatural, since you can get an entire x86 PC on a single chip, and things like calculators, cheap media players, and various toys also use nothing more than one COB. Also, I'd say that this machine also nicely demonstrates that a CPU is a state machine - a rather large one.
- joefourier 3y ago
  Those surely wouldn’t count because they’re entire CPUs on one chip, the point is making a CPU from parts that aren’t, which is sometimes dodgy sure.
  - adrian_b 3y ago
    If you do not use ICs that are complete CPUs, the minimum number of ICs needed to make a CPU is achieved by using bit-slice RALU chips and sequencer chips, e.g. from the former AMD 2900 series. So the only reasonable way to express the complexity of a CPU is by the total numbers of gates and of flip-flops or latches, regardless how they are grouped into monolithic ICs.
    - phire 3y ago
      The AMD 2900 family is not intended for low IC count designs. They didn't come out until 1975, the Intel 8080 and Motorola 6800 were well established on the market by then, the MOS 6502 had just landed and the Zilog z80 was just around the corner. If a designer cared about chip count or cost, they used one of those. The AMD 2900 family squarely targeted at high-performance mini-computers. Not only could you chain 4bit slices together to make a 16 or 32bit ALU, but they could run at significantly higher clock speeds than both a microprocessor or a CPU made out of pure TTL logic. The 2901 ALUs might save you some TTL chips, but those sequencer chips require so much support logic and microcode ROMs that your new design might actually exceed the chip count of whatever TTL-only CPU it's replacing. But... the new CPU will be faster and much more flexible thanks to the microcode. The AMD 2900 family allowed minicomputer designs to stay relevant for a few extra years, but only until larger single-chip CPUs like the Intel 8086 and Motorola 68000 hit the market.
em3rgent0rdr 3y ago
> "The same circuit can be used to produce 8-bit music at up to 4300 samples per second if an R-2R ladder is used instead of LEDs, and it is the same circuit I used to produce the soundtrack for the "Bad Apple!!" video." I would suggest in the spirit of 1-bit computing that instead of doing 8-bit music, you could instead output 1-bit oversampled Delta Sigma Modulated audio.
helsinkiandrew 3y ago
This is fantastic, I find it deliciously ironic that a 16-bit, 0.012MIPS CPU uses a 20MIPS ATtiny13 for programming https://www.microchip.com/en-us/product/attiny13 https://www.microchip.com/en-us/product/attiny13 That $1 8 pin marvel itself can be used to output VGA video: https://hackaday.com/2011/08/31/vga-video-output-with-an-attiny/ https://hackaday.com/2011/08/31/vga-video-output-with-an-att...
gbraad 3y ago
A more 'formal' introduction is here: https://www.youtube.com/watch?v=3uzoFJyYQ5E https://www.youtube.com/watch?v=3uzoFJyYQ5E
__alexs 3y ago
How did Bad Apple become the go to demo video for projects like this? It's like Doom for things that can't quite play Doom.
magicalhippo 3y ago
I've been having fun thinking about computing in the post-apocalypse. The CPU itself isn't so bad. Heck a relay CPU is should be quite doable to build, as evidenced by the various people that have built them. It's mostly just laborious. The problem is memory. There's a reason for all the seemingly whacky ideas to implement memory back in the early days, like the torsion wire[1] delay line[2] which is pretty much like banging on a taut rope and recording the pulses that arrive at the other end. But it's quite tough to get any real density from what I can tell, without advanced manufacturing. [1]: https://nzeldes.com/HOC/DelayLine.htm https://nzeldes.com/HOC/DelayLine.htm [2]: https://en.wikipedia.org/wiki/Delay-line_memory https://en.wikipedia.org/wiki/Delay-line_memory
vintermann 3y ago
If we are talking about bit-serial CPUs, Olof Kindgren's SERV bears mention. It's a portable FPGA core rather than a breadboard, but it's bit-serial, RISC-V compliant and tiny!

137 points by freedude 3y ago

Looks like the site could not handle the traffic. https://web.archive.org/web/20230820212723/www.jiristepanovsky.cz/project.php?p=23cpu https://web.archive.org/web/20230820212723/www.jiristepanovs...

nickt 3y ago

If you don’t make it to the end of the article you may not see the massive rabbit hole down there that is the https://www.homebrewcpuring.org/ https://www.homebrewcpuring.org/ - some incredible projects there, I had no idea this was so popular!

artemonster 3y ago
I think this ring is 75% responsible for my choice of profession (HW Eng that designs CPUs) :)
- boesboes 3y ago
  I wish I ran into this 20 years ago, I got into the whole web application development business and now I’m stuck dreaming of transistors ;)
  - z500 3y ago
    I've been dreaming of transistors since I got a kit for some electronics projects as a kid, but after frying a few components I also went on to web applications. I designed a CPU in Logisim after watching Ben Eater's videos, but I don't know if I have it in me to turn it into a physical thing. I'd love to get one onto an FPGA, or if I won the lottery some day, have one fabricated.
ddingus 3y ago
Wow! No kidding!

wglb 3y ago

This is very impressive. It reminds me of David Conroy's FPGA emulation of the DEC alpha: http://fpgaretrocomputing.org/ http://fpgaretrocomputing.org/

emeraldd 3y ago

Home brew computers! The Magic-1 was one of my favorites to read about .. http://www.homebrewcpu.com/index.htm http://www.homebrewcpu.com/index.htm

userbinator 3y ago

Depending on where you place the line between a state machine and a CPU, my 16-bit system might actually be the CPU with the lowest amount of ICs. Comparisons like this have always seemed a bit unnatural, since you can get an entire x86 PC on a single chip, and things like calculators, cheap media players, and various toys also use nothing more than one COB. Also, I'd say that this machine also nicely demonstrates that a CPU is a state machine - a rather large one.

joefourier 3y ago
Those surely wouldn’t count because they’re entire CPUs on one chip, the point is making a CPU from parts that aren’t, which is sometimes dodgy sure.
- adrian_b 3y ago
  If you do not use ICs that are complete CPUs, the minimum number of ICs needed to make a CPU is achieved by using bit-slice RALU chips and sequencer chips, e.g. from the former AMD 2900 series. So the only reasonable way to express the complexity of a CPU is by the total numbers of gates and of flip-flops or latches, regardless how they are grouped into monolithic ICs.
  - phire 3y ago
    The AMD 2900 family is not intended for low IC count designs. They didn't come out until 1975, the Intel 8080 and Motorola 6800 were well established on the market by then, the MOS 6502 had just landed and the Zilog z80 was just around the corner. If a designer cared about chip count or cost, they used one of those. The AMD 2900 family squarely targeted at high-performance mini-computers. Not only could you chain 4bit slices together to make a 16 or 32bit ALU, but they could run at significantly higher clock speeds than both a microprocessor or a CPU made out of pure TTL logic. The 2901 ALUs might save you some TTL chips, but those sequencer chips require so much support logic and microcode ROMs that your new design might actually exceed the chip count of whatever TTL-only CPU it's replacing. But... the new CPU will be faster and much more flexible thanks to the microcode. The AMD 2900 family allowed minicomputer designs to stay relevant for a few extra years, but only until larger single-chip CPUs like the Intel 8086 and Motorola 68000 hit the market.

em3rgent0rdr 3y ago

> "The same circuit can be used to produce 8-bit music at up to 4300 samples per second if an R-2R ladder is used instead of LEDs, and it is the same circuit I used to produce the soundtrack for the "Bad Apple!!" video." I would suggest in the spirit of 1-bit computing that instead of doing 8-bit music, you could instead output 1-bit oversampled Delta Sigma Modulated audio.

helsinkiandrew 3y ago

This is fantastic, I find it deliciously ironic that a 16-bit, 0.012MIPS CPU uses a 20MIPS ATtiny13 for programming https://www.microchip.com/en-us/product/attiny13 https://www.microchip.com/en-us/product/attiny13 That $1 8 pin marvel itself can be used to output VGA video: https://hackaday.com/2011/08/31/vga-video-output-with-an-attiny/ https://hackaday.com/2011/08/31/vga-video-output-with-an-att...

gbraad 3y ago

A more 'formal' introduction is here: https://www.youtube.com/watch?v=3uzoFJyYQ5E https://www.youtube.com/watch?v=3uzoFJyYQ5E

__alexs 3y ago

How did Bad Apple become the go to demo video for projects like this? It's like Doom for things that can't quite play Doom.

magicalhippo 3y ago

I've been having fun thinking about computing in the post-apocalypse. The CPU itself isn't so bad. Heck a relay CPU is should be quite doable to build, as evidenced by the various people that have built them. It's mostly just laborious. The problem is memory. There's a reason for all the seemingly whacky ideas to implement memory back in the early days, like the torsion wire[1] delay line[2] which is pretty much like banging on a taut rope and recording the pulses that arrive at the other end. But it's quite tough to get any real density from what I can tell, without advanced manufacturing. [1]: https://nzeldes.com/HOC/DelayLine.htm https://nzeldes.com/HOC/DelayLine.htm [2]: https://en.wikipedia.org/wiki/Delay-line_memory https://en.wikipedia.org/wiki/Delay-line_memory

vintermann 3y ago

If we are talking about bit-serial CPUs, Olof Kindgren's SERV bears mention. It's a portable FPGA core rather than a breadboard, but it's bit-serial, RISC-V compliant and tiny!