SCASM

Introduction

SCASM is an assembler for the DCPU-16 architecture used in the game 0x10c. See the game's official website for details on the instruction set. This assembler is different and powerful because the code you write is actually Ruby, meaning you can use all the capabilities of a high-level programming language to help generate the final machine code.

Installation

gem install scasm

Example

foo = A
bar = B
offset = 42
label "loop"
add [foo, offset], bar
set pc, "loop"

See the examples directory for more sample code.

Syntax

SCASM input is Ruby code, but you won't need a deep understanding of Ruby to get started. Simple statements like add A, 1 work just like you expect. This section will cover the SCASM-specific syntax.

Instructions

To emit an instruction just write its lower-case name followed by the values:

add A, 1
jsr X

The one exception is the and instruction, which must be written as and_ because and is a reserved word in Ruby.

Pseudoinstructions

• jmp label - Equivalent to set pc, label.
• ret - Equivalent to set pc, pop.

To make your own pseudoinstructions/macros just define a Ruby method. For example, here's how jmp is implemented:

def jmp label
  set pc, label
end

Registers

Ruby variables named A, B, C, X, Y, Z, I, and J are provided to refer to the processor registers.

Memory

Memory references are of the form [register, offset]. Either register or offset can be omitted.

Examples:

• [A]
• [0x100]
• [A, 2]

Literals

Literal values are just given as integers. Example: 42 or 0x200.

Labels

Labels are defined by the label statement. To refer to a label, just use its name. For example:

label "loop"
add A, 1
set pc, "loop"

Data

Use the data statement to put arbitrary words into the binary.

label "sin_lookup_table"
data 0, 0x38f6, 0x6f12, 0x9f9c, 0xc825, 0xe6a4, 0xf993, 0xffff

Miscellaneous

These values have the same meaning as in the spec:

• pop
• peek
• push
• sp
• pc
• o

Standard Assembly Syntax

SCASM also supports the normal DCPU-16 assembly syntax. Just pass a string to the asm method:

asm <<-EOS
  add [1+A], 5
EOS

Contributing

Fork the project on GitHub and send me a pull request.