Dumb8-CPU

Continuing my exploration of the lower-level world…

This project is the implementation of a CPU in a high-level language, C.
It aims to have a reduced (minimalist) instruction set and still be
Turing complete. In the future, I’d like to implement it in a hardware
description language such as VHDL or Verilog.

How to test

You can run a test program like that. I’ll try making a developer’s
manual so one can make its own programs using the custom assembly here.

das is the Dumb8 Assembler, which converts .asm files to .bin CPU
executables. dumb8 is the CPU emulator.

    make
    ./das program.asm
    ./dumb8 program.bin

Technical specifications

-   8-bit processing unit
-   RISC (reduced instruction set computer)
-   8 general purpose registers (labeled Rx)
-   1 input port, 1 output port (via getchar and putchar)
-   Turing-completeness: bitwise and arithmetic operations

Instruction set reference (for programmers)

    ; Move register RY to register RX
    MOV RX, RY

    ; Put value X in register RX
    PUT RX, X

    ; Arithmetic operations. Result stored in RX
    ADD RX, RY
    SUB RX, RY
    MUL RX, RY
    DIV RX, RY

    ; Bitwise operations stored in RX
    OR RX, RY
    AND RX, RY
    XOR RX, RY

    ; Output RX to screen
    OUT RX

    ; Input RX from keyboard
    IN RX

    ; Jump to memory offset ADDR (decimal)
    JMP ADDR

    ; Jump to memory offset ADDR (decimal) if equal flag is set by previous comparison
    JEQ ADDR

    ; Compare RX and RY, sets equal flag if true
    CMP RX, RY

    ; No operation; does nothing
    NOP

    ; Halts the processing unit
    HLT

Known bugs

-   If you find one, please contact me. Contributions are highly
    appreciated!