pyNES

The Legend

There was a time when game cartridges were forged in the fire of mount doom itself. That great power was then trapped into a regular plastic shelf. Most of the secrets were sealed by fellowship of hardcore game programmers. Their names were concealed in end-game credits from games that were never supposed to be finished. Countless game lives were wasted in the first level, in fruitless attempts of unveiling their evil[1] spell.

That was what my curious and inventive mind believed for years, and still do so. As a kid, I used to play those games and always asked myself how they were done. I really wanted to experience some of the game design problems the pioneers once faced. Back then, they had to wage their own tools, hack the specs for game effects and layout the memory mapper circuits. I figure out, that to reach mount doom as equal, foremost, I had to forge my own hammer. I've decided trail their footmarks therefore I build PyNES: A Python ASM compiler for Nintendo 8 bits.

However as I strum steps progresses, the anvil didn't sound the same. Knowledge weight has changed. Internet made it all available and communities are helpful. Also, computer power had grown and programming languages evolved. I must go a further in each step of their challenges. PyNES is turning into a high-level compiler which will allow Nintendo games to be written mostly in Python. This lecture will explain the several hacks and drawbacks of such approach. And I must say, trying to compile a such evolved language to a such limited processor as the c6502 it's MADNESS. It's pyNES!

The Untold Story

pyNES <http://gutomaia.net/pyNES> started as a regular 6502 assembler. However, writing games in ASM wasn't fun enough. Thus, using some AST hacks I tried to figure out a way of translating Python code into ASM.

Release notes

• pyNES versions 0.1.x is released as a Proof of concept.

Installation

Just use pip. It will give you a "pynes" command.

pip install pyNES

Hello, world

A simple "Hello, world" example. Given the example "hello.py"

import pynes
from pynes.bitbag import *

palette = [
    0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,
    0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,
    0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15
]

chr_asset = import_chr('player.chr')

sprite = define_sprite(128, 128, 0, 3)

def reset():
    global palette, sprite
    wait_vblank()
    clearmem()
    wait_vblank()
    load_palette(palette)
    load_sprite(sprite, 0)

Compile it with:

pynes py hello.py -o hello.nes

Now you can open hello.nes

How does it work?

In the above example, palette, chr_asset and sprite are constants. Each one has their own properties, since they are equally evaluated.

• palette is an int array. Int Arrays are static, and can't be changed.
• chr_asset Are reading structures.
• sprite is the sprite definition.

Functions are provided by bitbag package. Bitbag deals with templating[1] and some surrounding aspects needed by the asm code.

[1] Read "That's not all" at the end

That's not all folks

** pyNES 0.1.x **

Despite all my efforts, the pyNES version 0.1.x had several limitations as it should as a proof of concept.

Tricky limitations:

• Sprite collision
• Scrolling Screen
• Sprite animation
• Better joystick support
• Hard to extend

Being Hard to extend

** pyNES 0.2.x **

Therefore, pyNES version 0.2.x must overcome those limitations. And so far it is going great.

Project has been split into 4 projects:

• lexical - just the lexical analyzer
• nesasm_py - a 6502 ASM compiler based on NESASM
• pyNES - This project, wich must restrict it's responsibility just to
• pyNES_StdLib - Standard Library.

Mantras:

• No more templating.
• Less gaps between what you are writing and what the compiler is doing.
• Easier to extend

Hi Level Functions are not templated anymore. However, th

Example of waitvblank function:

@asm_function
def waitvblank():
    BIT('$2002')
    BPL(waitvblank)
    RTS()

That must be translated to:

waitvblank:
BIT $2002
BPL waitvblank
RTS