Octopus

This command line tool can do pre-processing on text based input files. It is intended for use with Octo-flavoured CHIP-8 assembly code, but it can be used with any text file.

Installing and running

Install Octopus as an NPM package, either for a project or globally:

npm install --save-dev @chipcode/octopus

You can then run Octopus on the command line:

npx octopus <input file> <output file> <option 1> <option 2>

Or you can use Octopus in your package.json file, for example to build a Cosmac VIP and a SUPERCHIP version of your project:

{
  "scripts": {
    "build": "npm run build-vip && npm run build-schip",
    "build-vip": "octopus ./src/index.8o ./bin/project-vip.8o VIP",
    "build-schip": "octopus ./src/index.8o ./bin/project-schip.8o SCHIP"
  }
}

Which you can then run using:

npm run build

Features

Conditional code inclusion

With Octopus, you can use :if, :unless, :else and :end in your code to switch on options, like so:

: store-values
  i := target
  save v2      # This doesn't increment i on SCHIP
  :if SCHIP    # Conditionally fix that issue
    vF := 3
    i += vF
  :end
  return

Now the conditional code between :if and :end will be included in the target file only if the option SCHIP is set.

Note that you can not use expressions, and options can only be either set (true) or unset (false). To set an option, give it as a parameter to the Octopus invocation or set it with :const (see below).

Here is a more complicated example, also showing the use of :else and :unless (which is basically "if not").

: store-values
  i := target
  :if XOCHIP
    save v3 - v4   # This XO-CHIP opcode doesn't increment i
  :else
    v0 := v3
    v1 := v4
    save v1        # This doesn't increment i on SUPERCHIP
  :end
  :unless VIP      # So on anything but VIP, we need to increment i manually
    vF := 2
    i += vF
  :end
  return

Set, reset and dump options

As described, options can be either set (true) or unset (false). You can set options by providing them to the Octopus invocation on the command line, or in your code with :const. If you set a constant to zero, it will be unset (false) from the perspective of Octopus. Any other value will be considered set (true).

  :if VIP
    :const USE_SCROLLING 0
  :else
    :const USE_SCROLLING 1
  :end

  # ...

  :if USE_SCROLLING
    scroll-down 8
  :end

When you're playing with options, and you run into issues, you can use the :dump-options command to instruct Octopus to output all those options that are set at that point in the program.

  :const OPTION_1 1
  :const OPTION_2 0
  :dump-options

  :const OPTION_2 1
  :dump-options

This will output:

Options on line 3: [ 'OPTION_1' ]
Options on line 6: [ 'OPTION_1', 'OPTION_2' ]

Include other files

When a project gets too large for a single source file, it is nice to be able to split it up into more logical segments. The Octopus :include command allows you to include another file into the current source file.

  :include "renderer.8o"
  :include "images/bitmaps.8o"

Including image files

If you wish to directly include an image file like a PNG file or a JPEG file as one or more sprites, you can do so through the image-loader plugin.

Automatic re-ordering of code

When writing XO-CHIP code, you need to keep the code that executes in the first 3.5K of memory. Beyond that you can have another 60K of data. This is because XO-CHIP does provide an instruction to load a 16-bit address into i (i := long <label>), but no instructions to jump to or call a 16-bit label.

However, when writing code it is much more convenient to be able to keep the code and the data that the code operates on close together. Octopus can automatically solve this issue for you, if you annotate your code with :segment code and :segment data.

Each file is considered to automatically start with :segment code, so you can leave that out if your file does indeed start with executable code.

  i := long table
  load v4
  # Do something intelligent with data...

:segment data

: table
  0 1 2 3 4