xasm - 6502 cross-assembler
===========================

xasm is a free tool for programming 
http://en.wikipedia.org/wiki/Atari_8-bit_family[Atari 8-bit family computers].

History
-------

First version of xasm was written in 1998. I needed a cross-assembler
that could understand the syntax of Quick Assembler
which I used for 8-bit Atari programming before I got a PC.
Initially xasm supported the syntax of QA and nothing more.
I quickly realized that I could extend the syntax to make it more expressive.
This led to xasm 2.0, still in 1998. I added some more features
next year. In 2002 I released many versions which contained
mostly bugfixes. In 2005 there were some minor enhancements and bug fixes,
as well as the whole assembler was rewritten from the x86 assembly language
it was initially written in to the http://www.digitalmars.com/d/[D programming language].
Current version 3.0.2 was released 17th October 2009.

Syntax
------

6502 assembler code is usually full of LDA, STA, LDA, STA sequences.
With xasm you can use MVA as a shortcut for LDA/STA pair
or even MWA for 16-bit transfers. You can avoid defining labels
when you need short jumps, thanks to conditional skip
and repeat pseudo-instructions. You can put two instructions
that share their argument in one line.
These are just some of the features that help you program
in a more concise way. Let's look at typical 6502 code
(which is also valid in xasm):

-----------------------------
        lda #<dest
        sta ptr
        lda #>dest
        sta ptr+1
        ldx #192
do_line
        ldy #39
do_byte
        lda pattern,y
        sta (ptr),y
        dey
        bpl do_byte
        lda #40
        clc
        adc ptr
        sta ptr
        bcc skip
        inc ptr+1
skip
        dex
        bne do_line
-----------------------------

Using xasm's features this code can be rewritten to:

-----------------------------
        mwa     #dest ptr
        ldx     #192
do_line
        ldy     #39
        mva:rpl pattern,y (ptr),y-
        lda #40
        add:sta ptr
        scc:inc ptr+1
        dex:bne do_line
-----------------------------


Usage
-----

xasm is a command-line tool.
Therefore you additionally need a programmer's text editor.

I use http://www.scintilla.org/SciTE.html[SciTE].
Syntax highlighting definition for it is included with xasm.
To install it, copy `xasm.properties` to the SciTE directory,
select _Options / Open Global Options File_, type `import xasm`
at the end and save the global configuration file.

image::scite.png[xasm code in SciTE]

Download
--------

- link:xasm-3.0.2-windows.zip[xasm 3.0.2 for Windows]
- link:xasm-3.0.2-src.zip[xasm 3.0.2 source code]
- link:xasm261.zip[xasm 2.6.1 for DOS]

For other systems, such as GNU/Linux and MacOS X, install a D 1.x compiler
and compile xasm from source code.

Inflate
-------

Do you need a good decompression routine for 6502?
See my link:inflate.html[inflate routine].

Links
-----

- http://atari800.sourceforge.net/[Atari800 emulator] - portable emulator of Atari 8-bit computers
- http://sources.pigwa.net/[Atari XL/XE Source Archive] - source code of Atari demos, utilities and games
- http://www.cc65.org/[cc65] - C cross-compiler targeting 6502-based systems
- http://epi.atari8.info/hcasm.php[HardCore Assembler] - 6502/65816 cross-assembler, partially supporting xasm's syntax
- http://mads.atari8.info/[MADS] - another 6502/65816 cross-assembler, partially supporting xasm's syntax
- http://wudsn.com/[WUDSN IDE] - Eclipse plugin, front-end to several 6502 cross-assemblers including xasm