Uxn-Logisim

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

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.
- 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
```
SFT isn’t implemented
ROT2/ROT2k are unimplemented
Probably a lot of other opcodes don’t work either

Quickstart

Open cpu.circ in Logisim
( 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)
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.