nandgame_logisim

Installation

Install logisim-evolution

https://snapcraft.io/logisim-evolution-snapcraft

download repo

project organization

source

Folder containing the logisim-evolution microprocessor

assembler

Folder containing the python assembler to convert assembly code to machine code

How to use

To compile your source code (written following nandgame's assembly rules) type : python assembleur.py to upload the machine code to the rom, open the project in logisim and right-click on the rom part in the CPU file. Select "Edit content" and then "open" at the bottom. Select the machine code file you assembled and it's good.

Assembler instructions examples

There are 2 registers A and D and one memory channel *A. *A is the memory value at RAM adress A. You can't use A and *A together in any operation (multiplexer thing)

arithmetic

A = D + A A = *A - D *A = *A - 1 D = D + 1 D = 0 A = 1

logic

A = D & A A = *A | D D = ~D

jumps

The program jumps at adresse A if the result of the previous operations validates the jump condition. E.g A = 0 ; JEQ jumps because the last op had an ALU resultequaling 0. You can right the jump in the same line as the computing or not. all possible jumps :

• A = 0 ; JEQ
• A = 3 ; JGT
• D = 1 ; JGE
• D - D ; JLE // no need to actually store the result
• D - 1 ; JLT
• ; JEQ // unconditionnal jump

Exception : A = 12 ; JMP // impoossible because all bits of the instruction are erased to store the immediate value, so no value assigning to A and jump in the same line

BEWARE

The RAM needs 1 cycle to ouput data after the input adress changed ! E;G if you want to do :

• A = SP
• *A = *A + 1

you have to skip a cycle in between (the way you want, this is an exemple) :

• A = SP // duplicate instruction
• A = SP
• *A = *A + 1