mirror of
https://github.com/fachat/xa65.git
synced 2024-11-16 15:07:54 +00:00
363 lines
14 KiB
HTML
363 lines
14 KiB
HTML
<html><head><title> xa 2.1.4 6502 Cross Assembler </title></head>
|
|
<body bgcolor="#ffffff">
|
|
<hr>
|
|
<h1 align=center> XA 2.1.4 </h1>
|
|
<h2 align=center> 65(c)02 Cross Assembler </h2>
|
|
<h2 align=center> (c) Andre Fachat </h2>
|
|
<h2 align=center> email: fachat@galileo.rhein-neckar.de </h2>
|
|
<hr>
|
|
<ol>
|
|
<li> what it is
|
|
<li> parameters and features
|
|
<li> 6502 Assembler
|
|
<li> pseudo-opcodes, block structures and where labels are valid
|
|
<li> pre-processor
|
|
<li> utilities
|
|
</ol><ul>
|
|
<li> literature
|
|
</ul>
|
|
|
|
<hr>
|
|
|
|
<h3> What it is </h3>
|
|
|
|
This Cross-Assembler makes programms for another computer that has a 6502-like
|
|
CPU. This CPU has been widely used in the famous Apple II, all the Commodore
|
|
8-Bit Computers (PET, VC20 and a derivate in the C64) and many others.
|
|
Some are still used in one-chip microcontrollers, e.g. the Rockwell modem
|
|
chipset.
|
|
All these chip share a common set of standard machine language commands,
|
|
some of them (e.g. the CMOS versions) have additional (software) features.
|
|
<p>
|
|
I had the idea for this assembler when I built my small 6502 System that
|
|
had place for 32kByte ROM to take the kernel and lots of other programms.
|
|
(After all, it became a multitasking micro-kernel with file-systems for
|
|
IBM and Commodore, I can even use the IBM drives as Floppy for my C64 with
|
|
this computer as controller. Piping and i/o-redirection included, of course)
|
|
Development on my old C64 began to suck with programms growing. So I decided
|
|
to do a Cross-Assembler on my new Atari ST.
|
|
<p>
|
|
First versions were very like the old Assembler on the C64, not really
|
|
using the resources (Reading all files two times completely etc).
|
|
With files growing the assembler also became more sophisticated.
|
|
Now hashcodes are used for mnemonics, preprocessor definition and label
|
|
search (Version >= 2.0.5). The files are only read once, putting the
|
|
preassembled code into memory (Version >= 2.0), taking it from there on pass 2.
|
|
Now it makes about 350kByte Source Code to about 30kByte ROM code in
|
|
less then 2 Minutes on an 8 MHz Atari ST with 2.5 MByte RAM and Harddisk.
|
|
(Well, the Atari is not fast. On my 486DX4/100 it takes about 2 seconds...)
|
|
But adding the whole relocation stuff slowed it down again.
|
|
<p>
|
|
<h3> Parameters and features</h3>
|
|
|
|
The assembler contains only a single programm called "xa" (for Atari: XA.TTP).
|
|
It takes one or more Source files into one object file, that can directly
|
|
be used.
|
|
But the assembler also has a mode to produce relocatable files, conforming
|
|
to the 'o65' fileformat (See fileformat.txt).
|
|
<p>
|
|
Call:
|
|
<p><pre>
|
|
xa [options] Source1 [Source2 ...]
|
|
</pre>
|
|
Object: this is the name, the output (object) file gets
|
|
Error: Here you will find the Error listing.
|
|
Label: this is the label list
|
|
<p><pre>
|
|
'-C' gives error codes when using CMOS-opcodes. Default is not to
|
|
complain.
|
|
'-c' do not produce o65 executable, but object files that can
|
|
contain undefined references.
|
|
'-v' go into verbose mode
|
|
'-x' old filename behaviour (overrides -o, -e and -l)
|
|
'-R' do not produce absolute code, but do relocation and all that.
|
|
'-o filename' set output filename
|
|
'-e filename' set errorlog filename
|
|
'-l filename' set labellist filename
|
|
'-r' add crossreference list to labellist output
|
|
(i.e list of filename/line where label is used)
|
|
'-M' allow ':' to appear in comments after a semicolon (MASM mode)
|
|
'-b? adr' set segment start address for ? = t(ext), d(ata), b(ss) or
|
|
z(ero) segment.
|
|
'-A adr' If the _file_ starts at adr in a ROM, then the text segment
|
|
need not be relocated. That of course only works, if the
|
|
data/bss/zero segments are not occupied by other programs too!
|
|
'-G' omit writing the exported globals to the file.
|
|
'-B' Show lines with '.(' or '.)' pseudo opcodes
|
|
'-Llabel' defines 'label' as absolute, undefined reference
|
|
'-DDEF=TEXT' define a preprocessor replacement
|
|
'-Ipath' additional include path for include files. Is evaluated before
|
|
the XAINPUT environment variable. One path per '-I',
|
|
multiple '-Ipath' allowed.
|
|
</pre>
|
|
|
|
Omitting the errorfile or labelfile Parameter will cause xa to not
|
|
write these files. Using '-x' will cause xa to take the name of the
|
|
first source file and change the extension (on an Atari there is only
|
|
one, like in DOS) to 'obj', 'err' and 'lab' respectively - if the old
|
|
behaviour is selected with the '-x' option or the files are defined with
|
|
"-l" and "-e". If no output file is given, "a.o65" is used.
|
|
<p>
|
|
<h4> Environment variables: </h4>
|
|
You can use the variables XAOUTPUT and XAINPUT to adjust the directory
|
|
structure. If source or include files are not found, the Path in XAINPUT
|
|
is being searched for the files. The different paths are separated by a
|
|
comma (','). XAINPUT gives the directory where the *.obj, *.err and
|
|
*.lab files are put.
|
|
If they are not set, there will be no search, respectively the files
|
|
are saved to the current directory.
|
|
<p>
|
|
The label file is a readable ASCII-file and lists all the labels
|
|
together with their block-count (see below) and their address.
|
|
The error file lists the version of the assembler, date and time of the
|
|
assembler run, all the error messages and the stuff being printed
|
|
with #echo and #print and last but not least a statistics of used
|
|
resources.
|
|
|
|
<h3> 6502 Assembler </h3>
|
|
|
|
xa supports both the standard 6502 opcodes as well as the CMOS versions
|
|
(Rockwell 65c02). Not supported are the 6502 undocumented opcodes, they have
|
|
to be put in by hand (with ".byte" directives).
|
|
<p>
|
|
For an introduction to 6502 Assembler please see elsewhere. A (very) short
|
|
introduction is given in the german version of this text.
|
|
<p>
|
|
|
|
<h4>Some Assembler specific details:</h4>
|
|
|
|
When using addressing modes that could be zeropage or absolute, zeropage
|
|
will be taken if possible. This can be prevented by prefixing the address
|
|
with a '!'. Then absolute addressing is taken, regardless of the address.
|
|
<p>
|
|
Values or Addresses can be expressed by arithmetik expressions with
|
|
hierachy and bracket. The following operands are understood:
|
|
<p><pre>
|
|
123 -decimal
|
|
$234 -hexadecimal
|
|
&123 -octal
|
|
%010110 -binary
|
|
* -program counter
|
|
"A" -ASCII-code
|
|
labelx -label
|
|
-(lab1+1) -expression
|
|
</pre>
|
|
The following operands can be used (third column is priority):
|
|
<p><pre>
|
|
+ -addition 9
|
|
- -subtraction 9
|
|
* -multiplication 10
|
|
/ -integer-division 10
|
|
<< -shift left 8
|
|
>> -shift right 8
|
|
>=,=> -more or equal 7
|
|
<=,=< -less or equal 7
|
|
< -less 7
|
|
> -more 7
|
|
= -equal 6
|
|
<>,>< -not equal 6
|
|
&& -logical AND 2
|
|
|| -Logical OR 1
|
|
& -Bitwise AND 5
|
|
| -Bitwise OR 3
|
|
^ -Bitwise XOR 4
|
|
</pre>
|
|
Operators with higher priority are evaluated first.
|
|
Brackets can be used as usual.
|
|
<p>
|
|
Valid expressions are, e.g.:
|
|
<p><pre>
|
|
LDA base+number*2,x
|
|
</pre>
|
|
For Addressing modes that do not start with a bracket, you can even use
|
|
a bracket at the beginning of an expression. Otherwise try this:
|
|
<p><pre>
|
|
LDX (1+2)*2,y ; Wrong!
|
|
LDX 2*(1+2),y ; Right!
|
|
</pre>
|
|
Before an expression you can use these unitary operators:
|
|
<p><pre>
|
|
< Gives the low byte of the expression
|
|
> Gives the high byte
|
|
|
|
LDA #<adresse
|
|
</pre>
|
|
Single Assembler statements are being separated by a ':' (You remember
|
|
the C64 :-) or a newline. Behind Each statement, separated by a ';'
|
|
you can write some comments. The next colon or a newline ends the
|
|
comment and starts a new statement.
|
|
In MASM compatibility mode ('-M' command line option), then a colon
|
|
in a comment is ignored, i.e. the comment lasts till the newline.
|
|
<p>
|
|
<h3> Pseudo opcodes, Block structures and where Labels are valid </h3>
|
|
|
|
In addition to the 6502 opcodes you have the following Pseudo opcodes:
|
|
<p><pre>
|
|
.byt value1,value2,value3, ...
|
|
.word value1,value2, ...
|
|
.asc "text1","text2", ...
|
|
.dsb length ,fillbte
|
|
.fopt value1, value2, ...
|
|
.text
|
|
.data
|
|
.bss
|
|
.zero
|
|
.align value
|
|
*=
|
|
.(
|
|
.)
|
|
|
|
</pre>
|
|
'.byt' and '.asc' are identical and save values to the memory (object file)
|
|
bytewise. '.word' does the same with words (2 Bytes).
|
|
'.dsb' fills a block with a given length with the value of fillbyte.
|
|
If fillbyte is not given, zero is taken.
|
|
<p>
|
|
'*=' changes the programm counter. The programm counter is not saved
|
|
to the file as no rewind is being done. Just the internal counter
|
|
is reloaded.
|
|
If a value is given when the assembler has been started in relocation mode
|
|
('-R command line option), the assembler goes into no-relocation mode, i.e
|
|
assembles everything without creating relocation table entries.
|
|
For '*=' without a value, the assembler switches back to relocation mode.
|
|
The absolute code is 'embedded' in the text segment, so the text segment
|
|
program counter is increased by the length of the absolute code.
|
|
<p>
|
|
'.(' opens a new 'block'. All labels in a block are local, i.e.
|
|
are only visible from inside the block - including sub-blocks.
|
|
An error is returned if a label is defined that is already defined
|
|
'above'.
|
|
With '.)' the block is closed. You can have a stack of up to 16 blocks
|
|
in each other (i.e. 16 times '.(' before the first '.)' will work, 17 not).
|
|
<p>
|
|
'.text', '.data', '.bss', '.zero' switch between the different segments.
|
|
The text segment is where the code goes in. The data segment is where
|
|
some initialized data goes in (it's actually like a second text segment).
|
|
The data segment might be allocated separated from the text segment.
|
|
The contents of the bss and the zero segment are not saved, just the
|
|
labels are evaluated. Here goes the uninitialized data stuff.
|
|
The zero segment allows allocation of zeropage space, bss is normal address
|
|
space.
|
|
These opcodes can be used in relative and absolute mode.
|
|
<p>
|
|
'.align' aligns the current segment to a byte boundary given by the
|
|
value. Allowed values are 2, 4, and 256. When using relative mode, the
|
|
align value is written to the file header, such that relocation keeps
|
|
the alignment.
|
|
<p>
|
|
'.fopt' works like ".byte", but saves the bytes as a fileoption (see
|
|
fileformat.txt). The length is computed automatically, so the first
|
|
byte in the ".fopt" list of values should be the type.
|
|
For example, the following line sets the filename for the object file.
|
|
<p><pre>
|
|
.fopt 0, "filename", 0
|
|
</pre>
|
|
A label is defined by not being an opcode:
|
|
<p><pre>
|
|
label1 LDA #0 ; assignes the programm counter
|
|
label2 =1234 ; explicit definition
|
|
label3 label4 label5 ; implicit programm counter
|
|
label6 label7 = 3 ; label6 becomes the program counter, while
|
|
; label7 is set to 3
|
|
label8: sta label2 ; As ':' divides opcodes, this is also
|
|
; working
|
|
</pre>
|
|
You can use more than one label for definition, except for explicit
|
|
definition.
|
|
Labels are case sensitive.
|
|
If a label is proceeded by a '+', this label is defined global.
|
|
If a label is proceeded by a '&', this label is defined one level 'up'
|
|
in the block hierachy, and you can use more than one '&'.
|
|
<p>
|
|
Redefinition of a label is possible by proceeding it with a dash '-'.
|
|
<p><pre>
|
|
-sysmem +=4 ; here you can use ==, +=, -=, *=, /=, &=, |=
|
|
-syszp =123
|
|
</pre>
|
|
|
|
<h3> Preprocessor </h3>
|
|
|
|
The preprocessor is very close to the one of the language C.
|
|
So in addition to the ';'-comments you can also use C-like
|
|
comments in '/*' and '*/'. Comments can be nested.
|
|
<p><pre>
|
|
#include "filename" includes a file on exactly this position.
|
|
if the file is not found, it is searched using
|
|
XAINPUT.
|
|
|
|
#echo comment gives a comment to the error file.
|
|
|
|
#print expression prints an expression to the error file (after
|
|
preprocessing and calculating)
|
|
|
|
#printdef DEFINED prints the definition of a preprocessor define to
|
|
the error file.
|
|
|
|
#define DEF text defines 'DEF' by 'text'
|
|
|
|
#ifdef DEF The source code from here to the following #endif
|
|
or #else is only assembled if 'DEF' is defined
|
|
with #define.
|
|
|
|
#else just else... (optionally)
|
|
|
|
#endif ends an #if-construct. This is a must to end #IF*
|
|
|
|
#ifndef DEF .... if DEF is not defined
|
|
|
|
#if expression .... if expression is not zero
|
|
|
|
#iflused label .... if a label has already been used
|
|
|
|
#ifldef label .... if a label is already defined
|
|
</pre>
|
|
#iflused and #ifldef work an labels, not on preprocessor defs! With these
|
|
commands a kind of library is easily built:
|
|
<p><pre>
|
|
#iflused label
|
|
#ifldef label
|
|
#echo label already defined, not from library
|
|
#else
|
|
label lda #0
|
|
....
|
|
#endif
|
|
#endif
|
|
</pre>
|
|
You can have up to 15 #if* on stack before the first #endif
|
|
<p>
|
|
You can also use #define with functions, like in C.
|
|
<p><pre>
|
|
#define mult(a,b) ((a)*(b))
|
|
</pre>
|
|
The preprocessor also allows continuation lines. I.e. lines that end
|
|
with a '\' directly before the newline have the following line
|
|
concatenated to it.
|
|
<p>
|
|
<h3> Utilities </h3>
|
|
|
|
There now are a few utilities that come with the assembler:
|
|
<p><pre>
|
|
file65 : prints some information about an o65 file. Can compute the
|
|
"-A" parameter for xa, to built the following file in a ROM.
|
|
reloc65 : relocates o65 files.
|
|
mkrom.sh: example shell (bash) script to show how to use the file65 utility
|
|
to build a ROM image with several in the ROM runnable programs.
|
|
ld65 : a linker for o65 files. The given files are linked together and
|
|
one o65 executable file is produced. All header options of all files
|
|
are put in the new file. There must not be any undefined reference
|
|
left, otherwise the output file is corrupt, because
|
|
for now, ld65 cannot produce object files. But you get a warning.
|
|
</pre>
|
|
<p>
|
|
<h3> Literature </h3>
|
|
<ul>
|
|
<li> "Das Maschinensprachebuch zum Commodore 64" <br>
|
|
Lothar Englisch, Data Becker GmbH
|
|
<li> "Controller Products Data Book" <br>
|
|
Rockwell International, Semiconductor Products Division
|
|
<li> "Programmieren in C" <br>
|
|
Kernighan, Ritchie, Hanser Verlag
|
|
</ul>
|
|
</body>
|
|
</html>
|