Uxn-Logisim

Implements the Uxn instruction set in digital hardware. Very WIP.

Contents

• cpu.circ - The Logisim file
• microcode.mc - Microcode source file
• microcode-asm.py - Microcode assembler
• opcodes.py - Definitions for where opcodes live in the microcode ROM

Known Bugs

• The program counter doesn't reset to 0x0100
  • To fix this, hold down the Reset button attached to the program counter and press Ctrl-T twice to advance the clock. This should set it to 0x0100 and program execution can begin.
  • Alternatively, type a0 01 00 2c into the first four bytes of the zero-page to make the cpu jump to the start
  • If your ROM contains absolute addressing then you'll need to manualy zero-pad it to start at 0x0100

    cat /dev/zero | head -c 256 > zero-page.rom
    cat zero-page.rom someprogram.rom > padded-program.rom

Quickstart

1. Open cpu.circ in Logisim

2. ( Optional ) Build the latest microcode

   i. To assemble the microcode rom file run

   python microcode-asm.py microcode.mc microcode.tal
   uxnasm microcode.tal microcode.rom

   ii. Right click on the ROM labelled Microcode_ROM

   iii. Load Image > Select microcode.rom > Select binary (big-endian)

3. Load the Uxn ROM you wish to load.

   i. Right click on the 64K RAM module ii. Load Image > Select a UXN rom > Select binary (big-endian)

Microcode Format

TODO

Microcode Assembler

The microcode assembler is only a partial assembler and relies upon Uxntal assembly for the conversion to binary. It takes in a [format](Microcode Format) similar to tal, and outputs a valid .tal file (Including comments!). Requires uxnasm or asma.tal to assemble into the microcode rom.