xasm is a 6502 cross-assembler with original syntax extensions. By default it generates binaries for Atari 8-bit computers.
6502 assembly code is full of LDA, STA, LDA, STA sequences. With xasm you can use MVA as a shortcut for an LDA/STA pair or even MWA for 16-bit transfers. Short branches can be replaced with conditional skip and repeat pseudo-instructions. You can use a pair of instructions with a shared argument. 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
xasm syntax is an extension of Quick Assembler's (created in 1991 for Atari 8-bit).
Accumulator shifts should be written as in
Whitespace is important: it is required before the instruction
and disallowed in the operands, because it separates a comment from the operand, e.g.
lda #0 this is a comment, no need for a semicolon
This may look weird at first, but it enables nice features such as instruction pairs and two-argument pseudo-instructions.
xasm is a command-line tool. Therefore you additionally need a programmer's text editor.
I use SciTE.
To install xasm syntax highlighting and single-keystroke compilation,
xasm.properties to the SciTE directory.
For single source file programs, press Ctrl+F7 to compile. You can double-click error messages to go to the incorrect line. Press F5 to run the program in the emulator.
For larger projects, I use GNU Make. Press F7 to build (and possibly run)
a project as described in the
Makefile. You can find my Makefiles in
my repositories on GitHub.
If you prefer VIM, see a link below.
xasm 3.1.0 for Windows, OS X, Ubuntu and Fedora.
- Atari800 - portable emulator of Atari 8-bit computers
- Atari XL/XE Source Archive - source code of Atari demos, utilities and games
- cc65 - C cross-compiler targeting 6502-based systems
- MADS - another 6502/65816 cross-assembler, partially supporting xasm's syntax
- vim-xasm - VIM syntax highlighting for xasm
- WUDSN IDE - Eclipse plugin, front-end to several 6502 cross-assemblers, including xasm