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96 lines
3.1 KiB
Markdown
96 lines
3.1 KiB
Markdown
xasm
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====
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xasm is a 6502 cross-assembler with original syntax extensions.
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By default it generates binaries
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for [Atari 8-bit computers](http://en.wikipedia.org/wiki/Atari_8-bit_family).
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Syntax
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------
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6502 assembly code is full of LDA, STA, LDA, STA sequences.
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With xasm you can use MVA as a shortcut for an LDA/STA pair or even MWA for 16-bit transfers.
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Short branches can be replaced with conditional skip and repeat pseudo-instructions.
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You can use a pair of instructions with a shared argument.
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These are just some of the features that help you program in a more concise way.
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Let's look at typical 6502 code (which is also valid in xasm):
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lda #<dest
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sta ptr
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lda #>dest
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sta ptr+1
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ldx #192
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do_line
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ldy #39
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do_byte
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lda pattern,y
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sta (ptr),y
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dey
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bpl do_byte
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lda #40
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clc
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adc ptr
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sta ptr
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bcc skip
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inc ptr+1
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skip
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dex
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bne do_line
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Using xasm's features this code can be rewritten to:
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mwa #dest ptr
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ldx #192
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do_line
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ldy #39
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mva:rpl pattern,y (ptr),y-
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lda #40
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add:sta ptr
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scc:inc ptr+1
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dex:bne do_line
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xasm syntax is an extension of Quick Assembler's (created in 1991 for Atari 8-bit).
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Accumulator shifts should be written as in `asl @`.
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Whitespace is important: it is required before the instruction
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and disallowed in the operands, because it separates a comment from the operand, e.g.
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lda #0 this is a comment, no need for a semicolon
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This may look weird at first, but it enables nice features such as instruction pairs
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and two-argument pseudo-instructions.
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Usage
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-----
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xasm is a command-line tool.
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Therefore you additionally need a programmer's text editor.
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I use [SciTE](http://www.scintilla.org/SciTE.html).
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To install xasm syntax highlighting and single-keystroke compilation,
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copy `xasm.properties` to the SciTE directory.
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For single source file programs, press Ctrl+F7 to compile.
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You can double-click error messages to go to the incorrect line.
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Press F5 to run the program in the emulator.
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For larger projects, I use GNU Make. Press F7 to build (and possibly run)
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a project as described in the `Makefile`. You can find my Makefiles in
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[my repositories](https://github.com/pfusik?tab=repositories) on GitHub.
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If you prefer VIM, see a link below.
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Download
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--------
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[xasm 3.1.0](https://github.com/pfusik/xasm/releases) for Windows, OS X, Ubuntu and Fedora.
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Links
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-----
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* [Atari800](http://atari800.sourceforge.net/) - portable emulator of Atari 8-bit computers
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* [Atari XL/XE Source Archive](http://sources.pigwa.net/) - source code of Atari demos, utilities and games
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* [cc65](http://cc65.github.io/cc65/) - C cross-compiler targeting 6502-based systems
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* [MADS](http://mads.atari8.info/) - another 6502/65816 cross-assembler, partially supporting xasm's syntax
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* [vim-xasm](https://github.com/lybrown/vim-xasm) - VIM syntax highlighting for xasm
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* [WUDSN IDE](http://wudsn.com/) - Eclipse plugin, front-end to several 6502 cross-assemblers, including xasm
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