xasm -i -d DEBUG=1 -l listing.lst source.asx
xasm - 6502 cross-assembler
xasm [OPTIONS] SOURCE_FILE
xasm is a cross-assembler for the 6502 family processors.
SOURCE_FILE is the name of the source file (you may omit the default .asx extension). When invoked without any options, xasm assembles SOURCE_FILE and writes the result to an object file named SOURCE_FILE with the extension changed to .obx.
Specifies that lines skipped due to a false condition should be included in the listing file.
Defines a label. LABEL should be a valid label name. VALUE may be any expression (may reference to labels defined in source files). You may use several /d options to define many labels from the command line.
Excludes included files from the listing file.
Generates listing file. If LISTING_FILE is omitted, the listing filename is SOURCE_FILE with the extension changed to .lst.
Prints a rule for use in a Makefile. First line of the rule lists OBJECT_FILE as the target of the rule and all source files (including the ones specified by icl and ins directives) as dependencies. The second line contains the command line with OBJECT_FILE replaced by the make macro $@ and SOURCE_FILE replaced by the macro $<. Dollars in the command line are doubled. Your make or shell may require more escaping.
Sets output file name. The default is SOURCE_FILE with the extension changed to .obx.
Prints fully qualified file names in listing and error messages. This option works only on Windows and is silently ignored on other platforms.
Quiet mode. Prevents xasm from printing the logo and the summary.
Generates label table. If LABEL_FILE is omitted then the table is appended to the listing.
Issues a warning message for each label whose value is unused.
Alternatively, you may use Unix-style options, for example:
xasm -i -d DEBUG=1 -l listing.lst source.asx
Source files should be plain ASCII files. LF, CR, CR/LF and Atari ($9b) line terminators are supported. Labels and instructions are case-insensitive.
xasm is backward compatible with Quick Assembler. To compile QA sources with xasm, simply replace ATASCII-specific characters with their integer codes. You also have to update all OPT directives, but usually you can simply remove them.
Label is a symbol that represents a signed 32-bit integer. You define a label by putting its name at the beginning of a line (with no spaces before). The label will be assigned the current value of the origin counter (i.e. the address of the compiled instruction), unless you use it with the EQU directive where it is assigned the value of the argument.
Instructions and directives must be preceded with some whitespace. Without leading whitespace they are treated as label names. For example:
nop
is a 6502 instruction, whereas
nop
defines a label called nop.
Whole-line comments must start with a semicolon, an asterisk or a pipe, with optional label definition and spaces before. Here are examples of whole-line comments:
; this is a comment * so it is label | and this too
Lines with instructions (and selected directives) may be repeated. To assemble a single line several times, precede the repeat count with a colon, for example:
:4 asl @ table :32*5 dta 5
In lines with instructions or directives, a comment starts immediately after the instruction/directive has been successfully parsed. That is, in these lines xasm does not require a special character to start a comment.
lda foo ; this is a comment sta bar this too tax #0 tax has no operand, therefore #0 starts this comment
You may put two instructions in one line so they share the operand. For example:
eor:sta foo
is equivalent to
eor foo sta foo
Note that
lda:tax #0
is allowed because #0 is treated as a comment for tax.
Expressions are numbers combined with operators and brackets. You should use square brackets, because parentheses are reserved for 6502 indirect addressing.
A number is:
Abbreviations of Atari hardware registers are provided to save two characters ($d40e vs ^4e) and to facilitate porting software between Atari 8-bit computers and the Atari 5200 console. These are very similar machines, one of the biggest differences is the location of hardware registers.
Syntax | Chip | Value | Value (Atari 5200 mode opt g+) |
---|---|---|---|
^0x |
GTIA |
$D00x |
$C00x |
^1x |
GTIA |
$D01x |
$C01x |
^2x |
POKEY |
$D20x |
$E80x |
^3x |
PIA |
$D30x |
error (there’s no PIA chip) |
^4x |
ANTIC |
$D40x |
$D40x |
The opcode syntax represents the opcode byte of the instruction inside braces. The operand of the instruction is discarded and is needed only to recognize the addressing mode. The instruction should begin right after the left brace and the right brace should immediately follow the operand or the instruction. You can skip the operand if the addressing mode is fixed. Examples: {lda #}, {jsr}, {bne}, {jmp ()}, {sta a:,x}.
You can use the line repeat counter (#) in the repeated lines. It counts the iterations starting from zero. Examples:
:3 dta # ; generates three bytes: 0, 1, 2. line_lo :192 dta l(screen+40*#) line_hi :192 dta h(screen+40*#) dl :59 dta $4f,a(screen+40*#),0,$4f,a(screen+40*#),0
The following binary operators are supported:
+ Addition
- Subtraction
* Multiplication
/ Division
% Remainder
& Bitwise AND
| Bitwise OR
^ Bitwise XOR
<< Arithmetic shift left
>> Arithmetic shift right
== Equal
= Equal (same as ==)
!= Not equal
<> Not equal (same as !=)
< Less than
> Greater than
<= Less or equal
>= Greater or equal
&& Logical AND
|| Logical OR
The following unary operators are supported:
+ Plus (does nothing)
- Minus (changes the sign)
~ Bitwise NOT (complements all bits)
! Logical NOT (changes true to false and vice versa)
< Low (extracts the low byte)
> High (extracts the high byte)
The operator precedence is following:
first: [] (brackets)
+ - ~ < > (unary)
* / % & << >> (binary)
+ - | ^ (binary)
= == <> != < > <= >= (binary)
! (unary)
&& (binary)
last: || (binary)
Although the operators are similar to those used in C, C++ and Java, their priorities are different than in these languages.
Compare and logical operators assume that zero is false and a non-zero is true. They return 1 for true.
Expressions are calculated in signed 32-bit arithmetic. "Arithmetic overflow" error signals overflow of the 32-bit range.
Examples:
five equ 5 here equ *
You can turn any of these on or off. The default (if no OPT specified) is opt f-g-h+l+o+. Examples:
opt l- listing off opt l+o- listing on, object file off opt f+g+h- useful for Atari 5200 cartridges - raw output, 5200 hw regs
If Atari executable headers are enabled, you can include an operand prefix:
a: starts a new block even if it’s superfluous because the new address equals the current address.
f: is same as a:, but additionally generates a double-$FF prefix before the new header. This prefix is automatically generated at the beginning of the file (no need to include f: in the first ORG). Examples:
org $600 org f:$700 table org *+100
In the latter example table points to 100 bytes of uninitialized data (label is assigned with * before the ORG directive is executed).
Starting with version 2.6.0, xasm supports code that is relocated in the memory at runtime. Let’s say you want your code to be located on page zero. You can’t normally load it directly into this place, so you load it at a different address and then move in your program. org r: changes the address that it used for code generation but not the address used for generating Atari executable headers. Example:
org $8000 ldx #code_length-1 mva:rpl code_loaded,x z:code_zpage,x- jmp code_zpage code_loaded org r:$30 code_zpage jmp * ; ... or something more sensible code_length equ *-code_zpage
Note that both * and label definitions use the counter used for code generation. There is no direct access to the other counter, because I think this is not useful. If you really need it, you can always type something like:
where_am_i equ *-code_zpage+code_loaded
integers
bytes: b(200) or simply 200
words: a(10000)
low bytes of words: l(511) (byte 255)
high bytes of words: h(511) (byte 1)
You may enter many expressions in parentheses and combine different types of data in single line, separating things with commas.
You may also define a sine lookup table. The syntax is:
sin(center,amp,size,first,last)
where:
center is an integer which is added to every sine value
amp is the sine amplitude
size is the sine period
first,last define the range of sine arguments. They are optional. The default are 0,size-1.
Example:
dta a(sin(0,1000,256,0,63))
defines a table of 64 words representing a quarter of sine with the amplitude of 1000.
real numbers: r(-1.23456e12)
Real numbers are stored in the 6-byte Atari Floating-Point format.
text strings
ASCII strings: c'Text' or c"Text"
ANTIC strings: d'Text' or d"Text"
A character string consists of any number of characters surrounded by quotation marks. You can include the quotation marks in the string by doubling them. Placing a * character after a string inverts the highest bit in every byte of the string.
Examples of DTA:
dta b(1,2),3,a(1000,-1),l(12345,sin(0,127,256)) dta d"ANTIC"*,c'It''s a string',$9b
Specifies another file to be included in the assembly as if the contents of the referenced file appeared in place of the ICL statement. The included file may contain other ICL statements. The .asx extension is added if none given. Examples:
icl 'macros.asx' icl 'lib/fileio'
Note: for portability, use only relative paths and slash as the separator. This way your sources will compile under Windows and Linux.
May be used if the source file ends with something which shouldn’t be read by xasm (e.g. your notes). At the end of file it’s optional.
Copies every byte of the specified file into the object file and updates the origin counter, as if these bytes were defined with DTA. You may specify a range of the file to insert. The syntax is:
ins 'file'[,offset[,length]]
The first byte in a file has the offset of zero. If the offset is negative, it counts from the end of the file. Examples:
ins 'picture.raw' ins 'file',-256 insert last 256 bytes of file ins 'file',10,10 insert bytes 10..19 of file
run main
is equivalent to:
org $2e0 dta a(main)
Example:
ini showpic
Examples:
ert *>$c000 ert len1>$ff||len2>$ff
noscr equ 1 widescr equ 1 ift noscr lda #0 eli widescr lda #$23 els lda #$22 eif sta $22f
Note: the above example may be rewritten using the repeat line feature:
noscr equ 1 widescr equ 1 :noscr lda #0 :!noscr&&widescr lda #$23 :!noscr&&!widescr lda #$22 sta $22f
Pseudo commands are built-in macros. There are no user-defined macros in xasm.
If you have ever programmed a 6502, you must have noticed that you had to use a CLC before ADC for every simple addition.
xasm can do it for you. ADD replaces two instructions: CLC and ADC.
It is SEC and SBC.
These are branches to the previous instruction. They take no operand, because the branch target is the address of the previously assembled instruction or pseudo command. Example:
ldx #0 mva:rne $500,x $600,x+
The above code copies a 256-byte memory block from $500 to $600. Here is the same written with standard 6502 commands only:
ldx #0 copy_loop lda $500,x sta $600,x inx bne copy_loop
These are branches over the next instruction. No operand is required, because the target is the address of the instruction following the next instruction. Example:
lda #40 add:sta ptr scc:inc ptr+1
In the above example the 16-bit variable ptr is incremented by 40.
These are long branches. While standard branches (such as BNE) have range of -128..+127, these jumps have range of 64 kB. For example:
jne dest
is equivalent to:
seq:jmp dest
Increments a 16-bit word in the memory. Example:
inw dest
is equivalent to:
inc dest sne:inc dest+1
Each of these pseudo commands requires two operands and substitutes two commands:
mva source dest = lda source : sta dest mvx source dest = ldx source : stx dest mvy source dest = ldy source : sty dest
These pseudo commands require two operands and are combinations of two MV*'s: one to move the low byte, and the other to move the high byte. You can’t use indirect nor pseudo addressing mode with MW*. Destination must be an absolute address, optionally indexed. When source is also an absolute address, an mw* source dest expands to:
mv* source dest mv* source+1 dest+1
When source is an immediate value, an mw* #immed dest expands to:
mv* <immed dest mv* >immed dest+1
When <immed equals >immed and immed is not forward-referenced, xasm skips the second LD*:
mv* <immed dest st* dest+1
If possible, MWX and MWY use increment/decrement commands. For example, mwx #1 dest expands to:
ldx #1 stx dest dex stx dest+1
All addressing modes are entered in the standard 6502 convention except for the accumulator addressing mode, which should be marked with the @ character (as in Quick Assembler).
For Quick Assembler compatibility, there are two extra immediate addressing modes: < and >, which use the low/high byte of a 16-bit word constant. Unlike in Quick Assembler, you can alternatively use the more common syntax: #< and #>. Note the difference:
lda >$ff+5 ; loads 1 (>$104) lda #>$ff+5 ; loads 5 (0+5)
You can explicitly specify absolute (a:) and zero-page (z:) addressing modes.
Examples:
nop asl @ lda >$1234 assembles to lda #$12 lda $100,x lda 0 zero-page (8-bit address) lda a:0 absolute (16-bit address) jmp ($0a) lda ($80),y
There are pseudo addressing modes, which are similar to pseudo commands. You may use them just like standard addressing modes in all 6502 commands and pseudo commands, except for MWA, MWX and MWY:
cmd a,x+ = cmd a,x : inx cmd a,x- = cmd a,x : dex cmd a,y+ = cmd a,y : iny cmd a,y- = cmd a,y : dey cmd (z),y+ = cmd (z),y : iny cmd (z),y- = cmd (z),y : dey cmd (z,0) = ldx #0 : cmd (z,x) cmd (z),0 = ldy #0 : cmd (z),y cmd (z),0+ = ldy #0 : cmd (z),y : iny cmd (z),0- = ldy #0 : cmd (z),y : dey
fixed "Branch out of range" error message - was overstated by 256 bytes for backward branches
command-line options are now case-insensitive
on Windows error messages are printed in red, warnings in yellow
fixed a bug in OPT H- mode
made xasm compilable with the latest D compiler v1.010 (there were incompatible changes in the D language and library)
rewritten from the x86 assembly language to the D programming language - Linux version is now available and DOS is no longer supported
no limits for line length, number of ICLs, ORGs,IFTs and labels
Unix-style command-line options are supported
/e option is no longer supported
the label table is now sorted alphabetically
no more "Arithmetic overflow" and "Division by zero" errors for correct use of forward-referenced labels (bug found by Marcin Lewandowski)
an error was reported in the following correct code:
ift 0 foo equ 1 ift foo eif eif
(bug found by Adrian Matoga)
errors for non-existing INC @ and DEC @
negative numbers fixed in the listing
long file names are supported under Windows
label values are now 32-bit, not just 17-bit
command-line options /n and /s are no longer supported
fatal I/O errors (such as floppy not ready) no longer print the annoying "Abort, Retry, Ignore" message
version 2.5.1 broke Unix EOLs - fixed
version 2.5.1 omitted all blank/comment/label lines, unless /c was used
fixed assembling sources with Atari EOLs
blank/comment/label lines in false conditionals are now correctly omitted in listing
fixed another bug, very similar to the previous one, e.g.
ift 0 :label nop eif
reported "Label not defined before" error for the repeat count
OPT F+ causes ORG to fill the space between the old and the new location with $FFs
OPT G+ enables Atari 5200 mode for hardware register abbreviations
fixed a bug related to label definitions in conditionally skipped code, e.g.
ift 0 label eif
reported "No ORG specified" error for the label definition
fixed incorrect unary operator precedence
fixed wrong label value after a skip pseudo command
the assembler is .EXE (.COM caused problems with DJGPP make due to a bug in the DJGPP runtime)
the assembler executable is not compressed (so it occupies less space in the ZIP)
improved command-line parsing: options may be used before source file name, tab character is a valid separator, slash may be used as a directory separator
error and warning messages are written to stderr, not stdout
added == (equals) operator, which is equivalent to =, but more natural for C/C++/Java programmers
added /p option: print full paths in listing and error messages
fixed double skip (e.g. SCC:SNE)
fixed real numbers with two-digit exponent
trailing spaces are trimmed from listing lines
label definitions allowed in blank, comment and repeated lines
fixed invalid opcodes of absolute CPX and CPY
fixed: addressing mode not checked for branch commands
fixed ICL in last line
fixed OPT H-H+
fixed first ORG *
no need to set origin counter until it’s used
allow Unix, Macintosh and Atari EOLs
value of true changed to 1
command-line option to set environment variables on error
commane-line option to assemble only if source is newer than object file
fixed: name of object file was truncated
fixed forward references in EQU and DTA
fixed hex numbers
.OBX is now the default extension for the object file
options (command-line switches and OPT)
listing
label table
conditional assembly
user errors (ERT)
warnings
6 new pseudo commands (memory-to-memory move)
8 pseudo addressing modes
indirect conditional jumps
Atari floating-point numbers
object file headers optimization
improved expressions - 19 operators and brackets, 32-bit arithmetic
improved signed numbers
improved INS: inserting specified part of file
first release
Piotr Fusik <fox@scene.pl>
Website: http://xasm.atari.org