fasm - README

Introduction

fasm is an assembler for the Fonzie¹ virtual machine. You can use it to build binaries in the Delvecchio format. These binaries can be loaded and executed by the machine.

File format

The file format is similar to most x86 assemblers. You can define two sections in your source code:

• .data: DWORDs stored in the memory of the machine
• .code: instructions

The .data section is optional.

.data section

You can define variables in the .data section. The maximum length of a variable name is 16, the minimum length is one character. Letters, numbers and underscore are allowed in a variable name, but it cannot start with a number.

A valid .data section looks the following way:

.data
	f00_=900  ; first value
	_bar=2000 ; second value

As you can see here each instruction can end with a comment. Comments are introduced by a semicolon.

.code section

fasm uses Intel syntax. The mnemonics below are supported:

• mov
• inc
• dec
• sub
• add
• mul
• div
• and
• or
• rnd
• ret
• cmp
• je
• jne
• jge
• jg
• jle
• jl
• call
• ret
• pop
• push
• movs

You find a description of all available instructions in the Fonzie documentation.

This example shows how a complete source file can look like:

.data
	foo=900

.code
	mov a0, [foo] ; copy 900 to register a0
	mov a1, 100   ; copy 100 to register a1
	add a0, a1    ; add register a0 and a1, result is stored in r
	mov a0, r     ; copy r to a0
	cmp a0, a1    ; compare a1 to a0
	jl foobar     ; jump to subroutine if a1 is less than a1
	ret           ; without a return the subroutine foobar would be executed

foobar:
	mov a0, a1    ; copy a1 to a0
	ret

Label names follow the same rules as variable names.

Compiling source files

To compile a source file you have to specify two options: the source and the destination file:

fasm.exe --in=mysource.s --out=mybinary.bin

It's also possible to use a separate file for the data segment:

fasm.exe --in=mysource.s --datafile=mydata.bin --out=mybinary.bin

Building fasm

fasm is written in C#. The easiest way to build the executable is to compile it with MonoDevelop or Microsoft Visual Studio.

If you want to build fasm with the Mono compiler you can also use the Makefile.

Footnotes

1. Fonzie ↩