custom-assembler

This repository provides an assembler written in Python for a simulated CPU in Logisim, enabling the conversion of custom assembly code into machine code.

Getting started

Clone:

git clone https://github.com/Kenoalpe/custom-assembler.git

Change directory:

cd asm-compiler-excercise

Get required packages (Linux):

1. Create a virtual environment:
   1. venv in pycharm
2. Move into venv:
   1. source venv/bin/activate
3. Install requirements:
   1. python3 -m pip install -r requirements.txt

Run:

python3 -m app

How to use

It is important to notice that the output of this Assembler only works for a specific CPU made for this projekt.

Writing an Assembler File

To use the Assembler you'd have to write an Assembler file named asm.txt containing your instructions for your CPU programm.

This particular Assembler supports the following instructions:

Instruction	Definition
NOP	No Operation; does nothing and moves on to the next instruction after one CPU cycle
INPUT	Reads data from the external input field and writes it into register A
OUTPUT	Copies the content from register A to the output bus, where it's displayed in hex format
JMP <adress>	Jumps to <address> address in RAM
LOAD A,#<value>	Loads a constant <value> value in register A
LOAD A,<address>	Loads a value from <address> address of the RAM in register A
INC A	Increments register A by 1
INC B	Incrementes register B by 1
MOV B,A	Copies contents of register A into register B
ADD A,B	Calculates the sum of contens of register A and register B and writes the result in register A
SUB A,B	Calculates the difference of register A and register B and writes the result in register A
AND A,B	Does a bitwise and of contents of register A and register B and writes the result in register A
OR A,B	Doas a bitwise or of contents of register A and register B and writes the result in register A
EQUAL	Checks if content of register A and register B is the equal and writes the result in register A (0h if equal, else not equal)
BEQ <address>	Jumps to <address> adress in RAM if contents of regsiter A and register B are the same
STORE <address>	Stores the content of register A at <address> adress in the RAM
DB <value>	Definies a byte in the RAM
EQU <value>	Defines a constant for a label
RESB <number>	Reserves number of <number> bytes in RAM

You can also place comments. They beginn with a ; and end at the end of the line:

; This is a comment
INPUT ; this is a comment too 
; MOV B,A this whole line is a comment 

Additionally you can use labels: to acess your values and constants and define jump markers, like this:

my-byte-adress: DB 4A  ; Places a 0x4A at the position of this labeln in the RAM, can be used for instruction with a address parameter.
my-constant:    EQU 34 ; Definies a constant 0x34 at the position of this labeln in the RAM, can be used for instructions with a value paramter.
reverved-bytes: RESB 5 ; Definies 5 bytes, can be used for instruction with a address parameter, points to the first byte. Get placed where the instruction sits in the asm code.

my-jump-label:  MOV A,B
                INC A
                INC A

my-label:       SUB A,B
                AND A,B
                JMP my-jump-label

Now you can generate the machine code via python3 -m app This generates an output machine-code.txt file. You can now copy the contents of this file and paste them into your RAM of your Logisim CPU.

Well DONE!!!