Pickle RISC 16bit CPU

... so I would like to build a computer, this time a little closer to "from scratch".

Goals

• Fun!
• Aiming for a poorly defined balance between "easy to build" and "not too slow"
• Can run a multitasking OS
• Serve web site about itself (like Magic-1 does)
• Serial console interface
• Run at ~2MHz clock
  • 4MHz as a stretch goal :)
• Most instruction single cycle
• Probably RPi as a peripherial device, emulating a GPU, network card, storage, serial terminal...

State

• Instruction set
  • Kind of done, still being tweaked to match the HW limitations and to improve proramming experience
• HW design
  • Slightly more than a fuzzy idea of how stuff should should go together
  • The block diagram shows most of the general idea
  • There is a design document that contains some (incomplete) information
• SW
  • Skeleton of a toolchain written in Rust (toolchain-rs/)
  • Lisp interpreter is planned as a shell
    • Probably loosely based on Make a Lisp
    • Compiler as a stretch goal

Links

Inspiration

• Magic-1: http://www.homebrewcpu.com/
  • Showed me that there is so much magic in this topic.
  • I would like my machine to look like Magic-1 and do the stuff that Magic-1 does.
• Ben Eater's breadboard computer: https://www.youtube.com/playlist?list=PLowKtXNTBypGqImE405J2565dvjafglHU
  • Gave me the idea that I could actually build something like this.
• James Sharman's JAM-1: https://www.youtube.com/c/weirdboyjim/videos
  • Different goals, but just plain awesome :)

Instruction set

• ARM Thumb Instruction set
• AVR instruction set

Peripherials

• Interfacing SDHC card to 6502: https://github.com/gfoot/sdcard6502

The rest

• MUPS/16, a nice 16bit CPU with similar goals/design: http://mups16.net/pages/overview.html#overview
• RISC-V: https://riscv.org/wp-content/uploads/2017/05/riscv-spec-v2.2.pdf
• Simple almost C-like language: https://incoherency.co.uk/blog/stories/slang.html
• Logisim evolution
• Nandgame ALU https://nandgame.com/

  The ALU (Arithmetic/Logic Unit) performs one or more operations on two input values X and Y.

  The six flags select what operations to perform. Each flag trigger an operation when the flag is 1: zx Use 0 for X nx Invert X zy Use 0 for Y ny Invert Y f selects an operation: 0: output is X AND Y 1: output is X + Y no Invert output

  The flags can be combined and the specified order is significant.

  For example, if both zx and nx is 1, then X is inverted 0.