.DEBUGINFO
.ADDRSIZE
.BANK
.BANKBYTE
.BLANK
.CONCAT
.CONST
.HIBYTE
.HIWORD
.IDENT
.LEFT
.LOBYTE
.LOWORD
.MATCH
.MAX
.MID
.MIN
.REF, .REFERENCED
.RIGHT
.SIZEOF
.STRAT
.SPRINTF
.STRING
.STRLEN
.TCOUNT
.XMATCH
.A16
.A8
.ADDR
.ALIGN
.ASCIIZ
.ASSERT
.AUTOIMPORT
.BANKBYTES
.BSS
.BYT, .BYTE
.CASE
.CHARMAP
.CODE
.CONDES
.CONSTRUCTOR
.DATA
.DBYT
.DEBUGINFO
.DEFINE
.DELMAC, .DELMACRO
.DEF, .DEFINED
.DEFINEDMACRO
.DESTRUCTOR
.DWORD
.ELSE
.ELSEIF
.END
.ENDENUM
.ENDIF
.ENDMAC, .ENDMACRO
.ENDPROC
.ENDREP, .ENDREPEAT
.ENDSCOPE
.ENDSTRUCT
.ENDUNION
.ENUM
.ERROR
.EXITMAC, .EXITMACRO
.EXPORT
.EXPORTZP
.FARADDR
.FATAL
.FEATURE
.FILEOPT, .FOPT
.FORCEIMPORT
.GLOBAL
.GLOBALZP
.HIBYTES
.I16
.I8
.IF
.IFBLANK
.IFCONST
.IFDEF
.IFNBLANK
.IFNDEF
.IFNREF
.IFP02
.IFP4510
.IFP816
.IFPC02
.IFPSC02
.IFREF
.IMPORT
.IMPORTZP
.INCBIN
.INCLUDE
.INTERRUPTOR
.ISMNEM, .ISMNEMONIC
.LINECONT
.LIST
.LISTBYTES
.LOBYTES
.LOCAL
.LOCALCHAR
.MACPACK
.MAC, .MACRO
.ORG
.OUT
.P02
.P4510
.P816
.PAGELEN, .PAGELENGTH
.PC02
.POPCPU
.POPSEG
.PROC
.PSC02
.PUSHCPU
.PUSHSEG
.RELOC
.REPEAT
.RES
.RODATA
.SCOPE
.SEGMENT
.SET
.SETCPU
.SMART
.STRUCT
.TAG
.UNDEF, .UNDEFINE
.UNION
.WARNING
.WORD
.ZEROPAGE
.MACPACK generic
.MACPACK longbranch
.MACPACK apple2
.MACPACK atari
.MACPACK cbm
.MACPACK cpu
.MACPACK module
.ORG
keyword
.TAG
keyword
ca65 is a replacement for the ra65 assembler that was part of the cc65 C compiler, originally developed by John R. Dunning. I had some problems with ra65 and the copyright does not permit some things which I wanted to be possible, so I decided to write a completely new assembler/linker/archiver suite for the cc65 compiler. ca65 is part of this suite.
Some parts of the assembler (code generation and some routines for symbol table handling) are taken from an older crossassembler named a816 written by me a long time ago.
Here's a list of the design criteria, that I considered important for the development:
.import S1, S2
.export Special
Special = 2*S1 + S2/7
right.The assembler accepts the following options:
---------------------------------------------------------------------------
Usage: ca65 [options] file
Short options:
-D name[=value] Define a symbol
-I dir Set an include directory search path
-U Mark unresolved symbols as import
-V Print the assembler version
-W n Set warning level n
-d Debug mode
-g Add debug info to object file
-h Help (this text)
-i Ignore case of symbols
-l name Create a listing file if assembly was ok
-mm model Set the memory model
-o name Name the output file
-s Enable smart mode
-t sys Set the target system
-v Increase verbosity
Long options:
--auto-import Mark unresolved symbols as import
--bin-include-dir dir Set a search path for binary includes
--cpu type Set cpu type
--create-dep name Create a make dependency file
--create-full-dep name Create a full make dependency file
--debug Debug mode
--debug-info Add debug info to object file
--feature name Set an emulation feature
--help Help (this text)
--ignore-case Ignore case of symbols
--include-dir dir Set an include directory search path
--large-alignment Don't warn about large alignments
--listing name Create a listing file if assembly was ok
--list-bytes n Maximum number of bytes per listing line
--memory-model model Set the memory model
--pagelength n Set the page length for the listing
--relax-checks Relax some checks (see docs)
--smart Enable smart mode
--target sys Set the target system
--verbose Increase verbosity
--version Print the assembler version
---------------------------------------------------------------------------
Here is a description of all the command line options:
--bin-include-dir dir
Name a directory which is searched for binary include files. The option may be used more than once to specify more than one directory to search. The current directory is always searched first before considering any additional directories. See also the section about search paths.
--cpu type
Set the default for the CPU type. The option takes a parameter, which may be one of
6502, 6502X, 65SC02, 65C02, 65816, sweet16, HuC6280, 4510
--create-dep name
Tells the assembler to generate a file containing the dependency list for the assembled module in makefile syntax. The output is written to a file with the given name. The output does not include files passed via debug information to the assembler.
--create-full-dep name
Tells the assembler to generate a file containing the dependency list for the assembled module in makefile syntax. The output is written to a file with the given name. The output does include files passed via debug information to the assembler.
-d, --debug
Enables debug mode, something that should not be needed for mere mortals:-)
--feature name
Enable an emulation feature. This is identical as using .FEATURE
in the source with two exceptions: Feature names must be lower case, and
each feature must be specified by using an extra --feature
option,
comma separated lists are not allowed.
See the discussion of the
.FEATURE
command for a list of emulation features.
-g, --debug-info
When this option (or the equivalent control command .DEBUGINFO
) is
used, the assembler will add a section to the object file that contains
all symbols (including local ones) together with the symbol values and
source file positions. The linker will put these additional symbols into
the VICE label file, so even local symbols can be seen in the VICE
monitor.
-h, --help
Print the short option summary shown above.
-i, --ignore-case
This option makes the assembler case insensitive on identifiers and labels.
This option will override the default, but may itself be overridden by the
.CASE
control command.
-l name, --listing name
Generate an assembler listing with the given name. A listing file will never be generated in case of assembly errors.
--large-alignment
Disable warnings about a large combined alignment. See the discussion of the
.ALIGN
directive for further information.
--list-bytes n
Set the maximum number of bytes printed in the listing for one line of
input. See the
.LISTBYTES
directive
for more information. The value zero can be used to encode an unlimited
number of printed bytes.
-mm model, --memory-model model
Define the default memory model. Possible model specifiers are near, far and huge.
-o name
The default output name is the name of the input file with the extension replaced by ".o". If you don't like that, you may give another name with the -o option. The output file will be placed in the same directory as the source file, or, if -o is given, the full path in this name is used.
--pagelength n
sets the length of a listing page in lines. See the
.PAGELENGTH
directive for more information.
--relax-checks
Relax some checks done by the assembler. This will allow code that is an error in most cases and flagged as such by the assembler, but can be valid in special situations.
Examples are:
-s, --smart-mode
In smart mode (enabled by -s or the
.SMART
pseudo instruction) the assembler will track usage of the REP
and
SEP
instructions in 65816 mode and update the operand sizes
accordingly. If the operand of such an instruction cannot be evaluated by
the assembler (for example, because the operand is an imported symbol), a
warning is issued.
Beware: Since the assembler cannot trace the execution flow this may lead to false results in some cases. If in doubt, use the .ixx and .axx instructions to tell the assembler about the current settings. Smart mode is off by default.
-t sys, --target sys
Set the target system. This will enable translation of character strings and character constants into the character set of the target platform. The default for the target system is "none", which means that no translation will take place. The assembler supports the same target systems as the compiler, see there for a list.
Depending on the target, the default CPU type is also set. This can be
overriden by using the
--cpu
option.
-v, --verbose
Increase the assembler verbosity. Usually only needed for debugging purposes. You may use this option more than one time for even more verbose output.
-D
This option allows you to define symbols on the command line. Without a value, the symbol is defined with the value zero. When giving a value, you may use the '$' prefix for hexadecimal symbols. Please note that for some operating systems, '$' has a special meaning, so you may have to quote the expression.
-I dir, --include-dir dir
Name a directory which is searched for include files. The option may be used more than once to specify more than one directory to search. The current directory is always searched first before considering any additional directories. See also the section about search paths.
-U, --auto-import
Mark symbols that are not defined in the sources as imported symbols. This
should be used with care since it delays error messages about typos and such
until the linker is run. The compiler uses the equivalent of this switch
(
.AUTOIMPORT
) to enable auto imported
symbols for the runtime library. However, the compiler is supposed to
generate code that runs through the assembler without problems, something
which is not always true for assembler programmers.
-V, --version
Print the version number of the assembler. If you send any suggestions or bugfixes, please include the version number.
-Wn
Set the warning level for the assembler. Using -W2 the assembler will even warn about such things like unused imported symbols. The default warning level is 1, and it would probably be silly to set it to something lower.
Normal include files are searched in the following places:
-I
option
on the command line.CA65_INC
if it is defined.asminc
of the directory defined in the
environment variable CC65_HOME
, if it is defined.Binary include files are searched in the following places:
--bin-include-dir
option on the command line.The assembler accepts the standard 6502/65816 assembler syntax. One line may contain a label (which is identified by a colon), and, in addition to the label, an assembler mnemonic, a macro, or a control command (see section Control Commands for supported control commands). Alternatively, the line may contain a symbol definition using the '=' token. Everything after a semicolon is handled as a comment (that is, it is ignored).
Here are some examples for valid input lines:
Label: ; A label and a comment
lda #$20 ; A 6502 instruction plus comment
L1: ldx #$20 ; Same with label
L2: .byte "Hello world" ; Label plus control command
mymac $20 ; Macro expansion
MySym = 3*L1 ; Symbol definition
MaSym = Label ; Another symbol
The assembler accepts
.P02
command was given).
.PSC02
command was given).
.PC02
command was given).
.P816
command was given).
.P4510
command was given).In 65816 mode, several aliases are accepted, in addition to the official mnemonics:
CPA
is an alias for CMP
DEA
is an alias for DEC A
INA
is an alias for INC A
SWA
is an alias for XBA
TAD
is an alias for TCD
TAS
is an alias for TCS
TDA
is an alias for TDC
TSA
is an alias for TSC
6502X mode is an extension to the normal 6502 mode. In this mode, several mnemonics for illegal instructions of the NMOS 6502 CPUs are accepted. Since these instructions are illegal, there are no official mnemonics for them. The unofficial ones are taken from http://www.oxyron.de/html/opcodes02.html. Please note that only the ones marked as "stable" are supported. The following table uses information from the mentioned web page, for more information, see there.
ALR: A:=(A and #{imm})/2;
ANC: A:=A and #{imm};
Generates opcode $0B.ARR: A:=(A and #{imm})/2;
AXS: X:=A and X-#{imm};
DCP: {adr}:={adr}-1; A-{adr};
ISC: {adr}:={adr}+1; A:=A-{adr};
LAS: A,X,S:={adr} and S;
LAX: A,X:={adr};
RLA: {adr}:={adr}rol; A:=A and {adr};
RRA: {adr}:={adr}ror; A:=A adc {adr};
SAX: {adr}:=A and X;
SLO: {adr}:={adr}*2; A:=A or {adr};
SRE: {adr}:={adr}/2; A:=A xor {adr};
The 4510 is a microcontroller that is the core of the Commodore C65 aka C64DX. It contains among other functions a slightly modified 65CE02/4502 CPU, to allow address mapping for 20 bits of address space (1 megabyte addressable area). As compared to the description of the CPU in the C65 System Specification (updated version) uses these changes:
LDA (d,SP),Y
may also be written as LDA (d,S),Y
(matching the 65816 notataion).LBNE
" instead of
"BNE
"). This might change at a later implementation of the assembler.SWEET 16 is an interpreter for a pseudo 16 bit CPU written by Steve Wozniak for the Apple ][ machines. It is available in the Apple ][ ROM. ca65 can generate code for this pseudo CPU when switched into sweet16 mode. The following is special in sweet16 mode:
.LOCALCHAR
command.
R0
.. R15
. In sweet16 mode,
these identifiers are reserved words.
Please note that the assembler does neither supply the interpreter needed for SWEET 16 code, nor the zero page locations needed for the SWEET 16 registers, nor does it call the interpreter. All this must be done by your program. Apple ][ programmers do probably know how to use sweet16 mode.
For more information about SWEET 16, see http://www.6502.org/source/interpreters/sweet16.htm.
For literal values, the assembler accepts the widely used number formats: A preceding '$' or a trailing 'h' denotes a hex value, a preceding '%' denotes a binary value, and a bare number is interpreted as a decimal. There are currently no octal values and no floats.
Please note that when using the conditional directives (.IF
and friends),
the input must consist of valid assembler tokens, even in .IF
branches
that are not assembled. The reason for this behaviour is that the assembler
must still be able to detect the ending tokens (like .ENDIF
), so
conversion of the input stream into tokens still takes place. As a consequence
conditional assembly directives may not be used to prevent normal text
(used as a comment or similar) from being assembled.
All expressions are evaluated with (at least) 32 bit precision. An expression may contain constant values and any combination of internal and external symbols. Expressions that cannot be evaluated at assembly time are stored inside the object file for evaluation by the linker. Expressions referencing imported symbols must always be evaluated by the linker.
Sometimes, the assembler must know about the size of the value that is the result of an expression. This is usually the case, if a decision has to be made, to generate a zero page or an absolute memory references. In this case, the assembler has to make some assumptions about the result of an expression:
Note: If the assembler is not able to evaluate the expression at assembly time, the linker will evaluate it and check for range errors as soon as the result is known.
In the context of a boolean expression, any non zero value is evaluated as
true, any other value to false. The result of a boolean expression is 1 if
it's true, and zero if it's false. There are boolean operators with extreme
low precedence with version 2.x (where x > 0). The .AND
and .OR
operators are shortcut operators. That is, if the result of the expression is
already known, after evaluating the left hand side, the right hand side is
not evaluated.
Sometimes an expression must evaluate to a constant without looking at any
further input. One such example is the
.IF
command
that decides if parts of the code are assembled or not. An expression used in
the .IF
command cannot reference a symbol defined later, because the
decision about the .IF
must be made at the point when it is read. If the
expression used in such a context contains only constant numerical values,
there is no problem. When unresolvable symbols are involved it may get harder
for the assembler to determine if the expression is actually constant, and it
is even possible to create expressions that aren't recognized as constant.
Simplifying the expressions will often help.
In cases where the result of the expression is not needed immediately, the assembler will delay evaluation until all input is read, at which point all symbols are known. So using arbitrary complex constant expressions is no problem in most cases.
| Operator | Description | Precedence |
| Built-in string functions | 0 | |
| Built-in pseudo-variables | 1 | |
| Built-in pseudo-functions | 1 | |
| + | Unary positive | 1 |
| - | Unary negative | 1 |
|
~ .BITNOT | Unary bitwise not | 1 |
|
< .LOBYTE | Unary low-byte operator | 1 |
|
> .HIBYTE | Unary high-byte operator | 1 |
|
^ .BANKBYTE | Unary bank-byte operator | 1 |
| * | Multiplication | 2 |
| / | Division | 2 |
| .MOD | Modulo operator | 2 |
|
& .BITAND | Bitwise and | 2 |
|
^ .BITXOR | Binary bitwise xor | 2 |
|
<< .SHL | Shift-left operator | 2 |
|
>> .SHR | Shift-right operator | 2 |
| + | Binary addition | 3 |
| - | Binary subtraction | 3 |
|
| .BITOR | Bitwise or | 3 |
| = | Compare operator (equal) | 4 |
| <> | Compare operator (not equal) | 4 |
| < | Compare operator (less) | 4 |
| > | Compare operator (greater) | 4 |
| <= | Compare operator (less or equal) | 4 |
| >= | Compare operator (greater or equal) | 4 |
|
&& .AND | Boolean and | 5 |
| .XOR | Boolean xor | 5 |
|
|| .OR | Boolean or | 6 |
|
! .NOT | Boolean not | 7 |
To force a specific order of evaluation, parentheses may be used, as usual.
A symbol or label is an identifier that starts with a letter and is followed
by letters and digits. Depending on some features enabled (see
at_in_identifiers
,
dollar_in_identifiers
and
leading_dot_in_identifiers
)
other characters may be present. Use of identifiers consisting of a single
character will not work in all cases, because some of these identifiers are
reserved keywords (for example "A" is not a valid identifier for a label,
because it is the keyword for the accumulator).
The assembler allows you to use symbols instead of naked values to make the source more readable. There are a lot of different ways to define and use symbols and labels, giving a lot of flexibility.
Numeric constants are defined using the equal sign or the label assignment operator. After doing
two = 2
may use the symbol "two" in every place where a number is expected, and it is evaluated to the value 2 in this context. The label assignment operator is almost identical, but causes the symbol to be marked as a label, so it may be handled differently in a debugger:
io := $d000
The right side can of course be an expression:
four = two * two
Within macros and other control structures (
.REPEAT
, ...) it is sometimes useful to have some sort of
variable. This can be achieved by the .SET
operator. It creates a
symbol that may get assigned a different value later:
four .set 4
lda #four ; Loads 4 into A
four .set 3
lda #four ; Loads 3 into A
Since the value of the symbol can change later, it must be possible to evaluate it when used (no delayed evaluation as with normal symbols). So the expression used as the value must be constant.
Following is an example for a macro that generates a different label each time
it is used. It uses the
.SPRINTF
function
and a numeric variable named lcount
.
.lcount .set 0 ; Initialize the counter
.macro genlab
.ident (.sprintf ("L%04X", lcount)):
lcount .set lcount + 1
.endmacro
A label is defined by writing the name of the label at the start of the line (before any instruction mnemonic, macro or pseudo directive), followed by a colon. This will declare a symbol with the given name and the value of the current program counter.
Using the
.PROC
directive, it is possible to
create regions of code where the names of labels and symbols are local to this
region. They are not known outside of this region and cannot be accessed from
there. Such regions may be nested like PROCEDUREs in Pascal.
See the description of the
.PROC
directive for more information.
Cheap local labels are defined like standard labels, but the name of the
label must begin with a special symbol (usually '@', but this can be
changed by the
.LOCALCHAR
directive).
Cheap local labels are visible only between two non cheap labels. As soon as a
standard symbol is encountered (this may also be a local symbol if inside a
region defined with the
.PROC
directive), the
cheap local symbol goes out of scope.
You may use cheap local labels as an easy way to reuse common label names like "Loop". Here is an example:
Clear: lda #$00 ; Global label
ldy #$20
@Loop: sta Mem,y ; Local label
dey
bne @Loop ; Ok
rts
Sub: ... ; New global label
bne @Loop ; ERROR: Unknown identifier!
If you really want to write messy code, there are also unnamed labels. These labels do not have a name (you guessed that already, didn't you?). A colon is used to mark the absence of the name.
Unnamed labels may be accessed by using the colon plus several minus or plus characters as a label designator. Using the '-' characters will create a back reference (use the n'th label backwards), using '+' will create a forward reference (use the n'th label in forward direction). An example will help to understand this:
: lda (ptr1),y ; #1
cmp (ptr2),y
bne :+ ; -> #2
tax
beq :+++ ; -> #4
iny
bne :- ; -> #1
inc ptr1+1
inc ptr2+1
bne :- ; -> #1
: bcs :+ ; #2 -> #3
ldx #$FF
rts
: ldx #$01 ; #3
: rts ; #4
As you can see from the example, unnamed labels will make even short sections of code hard to understand, because you have to count labels to find branch targets (this is the reason why I for my part do prefer the "cheap" local labels). Nevertheless, unnamed labels are convenient in some situations, so it's your decision.
Note: Scopes organize named symbols, not unnamed ones, so scopes don't have an effect on unnamed labels.
While there are drawbacks with this approach, it may be handy in a few rare
situations. Using
.DEFINE
, it is possible
to define symbols or constants that may be used elsewhere. One of the
advantages is that you can use it to define string constants (this is not
possible with the other symbol types).
Please note: .DEFINE
style macros do token replacements on a low level,
so the names do not adhere to scoping, diagnostics may be misleading, there
are no symbols to look up in the map file, and there is no debug info.
Especially the first problem in the list can lead to very nasty programming
errors. Because of these problems, the general advice is, NOT do use
.DEFINE
if you don't have to.
Example:
.DEFINE two 2
.DEFINE version "SOS V2.3"
four = two * two ; Ok
.byte version ; Ok
.PROC ; Start local scope
two = 3 ; Will give "2 = 3" - invalid!
.ENDPROC
.DEBUGINFO
If
.DEBUGINFO
is enabled (or
-g is given on the command line), global, local and
cheap local labels are written to the object file and will be available in the
symbol file via the linker. Unnamed labels are not written to the object file,
because they don't have a name which would allow to access them.
ca65 implements several sorts of scopes for symbols.
All (non cheap local) symbols that are declared outside of any nested scopes are in global scope.
A special scope is the scope for cheap local symbols. It lasts from one non local symbol to the next one, without any provisions made by the programmer. All other scopes differ in usage but use the same concept internally.
A nested scoped for generic use is started with
.SCOPE
and closed with
.ENDSCOPE
.
The scope can have a name, in which case it is accessible from the outside by
using
explicit scopes. If the scope does not
have a name, all symbols created within the scope are local to the scope, and
aren't accessible from the outside.
A nested scope can access symbols from the local or from enclosing scopes by name without using explicit scope names. In some cases there may be ambiguities, for example if there is a reference to a local symbol that is not yet defined, but a symbol with the same name exists in outer scopes:
.scope outer
foo = 2
.scope inner
lda #foo
foo = 3
.endscope
.endscope
In the example above, the lda
instruction will load the value 3 into the
accumulator, because foo
is redefined in the scope. However:
.scope outer
foo = $1234
.scope inner
lda foo,x
foo = $12
.endscope
.endscope
Here, lda
will still load from $12,x
, but since it is unknown to the
assembler that foo
is a zeropage symbol when translating the instruction,
absolute mode is used instead. In fact, the assembler will not use absolute
mode by default, but it will search through the enclosing scopes for a symbol
with the given name. If one is found, the address size of this symbol is used.
This may lead to errors:
.scope outer
foo = $12
.scope inner
lda foo,x
foo = $1234
.endscope
.endscope
In this case, when the assembler sees the symbol foo
in the lda
instruction, it will search for an already defined symbol foo
.  So the assembler will use zeropage addressing mode. If
foo
is redefined later in scope inner
, the assembler tries to change
the address in the lda
instruction already translated, but since the new
value needs absolute addressing mode, this fails, and an error message "Range
error" is output.
Of course the most simple solution for the problem is to move the definition
of foo
in scope inner
upwards, so it precedes its use. There may be
rare cases when this cannot be done. In these cases, you can use one of the
address size override operators:
.scope outer
foo = $12
.scope inner
lda a:foo,x
foo = $1234
.endscope
.endscope
This will cause the lda
instruction to be translated using absolute
addressing mode, which means changing the symbol reference later does not
cause any errors.
A nested procedure is created by use of
.PROC
. It
differs from a
.SCOPE
in that it must have a
name, and a it will introduce a symbol with this name in the enclosing scope.
So
.proc foo
...
.endproc
is actually the same as
foo:
.scope foo
...
.endscope
This is the reason why a procedure must have a name. If you want a scope
without a name, use
.SCOPE
.
Note: As you can see from the example above, scopes and symbols live in
different namespaces. There can be a symbol named foo
and a scope named
foo
without any conflicts (but see the section titled
"Scope search order").
Structs, unions and enums are explained in a
separate section, I do only cover them here, because if they are declared with a
name, they open a nested scope, similar to
.SCOPE
. However, when no name is specified, the behaviour is
different: In this case, no new scope will be opened, symbols declared within
a struct, union, or enum declaration will then be added to the enclosing scope
instead.
Accessing symbols from other scopes is possible by using an explicit scope
specification, provided that the scope where the symbol lives in has a name.
The namespace token (::
) is used to access other scopes:
.scope foo
bar: .word 0
.endscope
...
lda foo::bar ; Access foo in scope bar
The only way to deny access to a scope from the outside is to declare a scope
without a name (using the
.SCOPE
command).
A special syntax is used to specify the global scope: If a symbol or scope is preceded by the namespace token, the global scope is searched:
bar = 3
.scope foo
bar = 2
lda #::bar ; Access the global bar (which is 3)
.endscope
The assembler searches for a scope in a similar way as for a symbol. First, it looks in the current scope, and then it walks up the enclosing scopes until the scope is found.
However, one important thing to note when using explicit scope syntax is, that a symbol may be accessed before it is defined, but a scope may not be used without a preceding definition. This means that in the following example:
.scope foo
bar = 3
.endscope
.scope outer
lda #foo::bar ; Will load 3, not 2!
.scope foo
bar = 2
.endscope
.endscope
the reference to the scope foo
will use the global scope, and not the
local one, because the local one is not visible at the point where it is
referenced.
Things get more complex if a complete chain of scopes is specified:
.scope foo
.scope outer
.scope inner
bar = 1
.endscope
.endscope
.scope another
.scope nested
lda #outer::inner::bar ; 1
.endscope
.endscope
.endscope
.scope outer
.scope inner
bar = 2
.endscope
.endscope
When outer::inner::bar
is referenced in the lda
instruction, the
assembler will first search in the local scope for a scope named outer
.
Since none is found, the enclosing scope (another
) is checked. There is
still no scope named outer
, so scope foo
is checked, and finally
scope outer
is found. Within this scope, inner
is searched, and in
this scope, the assembler looks for a symbol named bar
.
Please note that once the anchor scope is found, all following scopes
(inner
in this case) are expected to be found exactly in this scope. The
assembler will search the scope tree only for the first scope (if it is not
anchored in the root scope). Starting from there on, there is no flexibility,
so if the scope named outer
found by the assembler does not contain a
scope named inner
, this would be an error, even if such a pair does exist
(one level up in global scope).
Ambiguities that may be introduced by this search algorithm may be removed by
anchoring the scope specification in the global scope. In the example above,
if you want to access the "other" symbol bar
, you would have to write:
.scope foo
.scope outer
.scope inner
bar = 1
.endscope
.endscope
.scope another
.scope nested
lda #::outer::inner::bar ; 2
.endscope
.endscope
.endscope
.scope outer
.scope inner
bar = 2
.endscope
.endscope
ca65 assigns each segment and each symbol an address size. This is true, even if the symbol is not used as an address. You may also think of a value range of the symbol instead of an address size.
Possible address sizes are:
Since the assembler uses default address sizes for the segments and symbols, it is usually not necessary to override the default behaviour. In cases, where it is necessary, the following keywords may be used to specify address sizes:
The assembler assigns an address size to each segment. Since the representation of a label within this segment is "segment start + offset", labels will inherit the address size of the segment they are declared in.
The address size of a segment may be changed, by using an optional address
size modifier. See the
segment directive
for
an explanation on how this is done.
The address size of a symbol can be specified with a prefix:
The zeropage addressing override can be used to ensure the use of optimal zeropage instructions, or correct cases where the size isn't yet known due to the single-pass assembly model.
The larger addressing overrides can be used to promote a smaller address to absolute or far addressing, instead of being automatically fit into a smaller addressing type.
The default address size of a segment depends on the memory model used. Since labels inherit the address size from the segment they are declared in, changing the memory model is an easy way to change the address size of many symbols at once.
Pseudo variables are readable in all cases, and in some special cases also writable.
*
Reading this pseudo variable will return the program counter at the start of the current input line.
Assignment to this variable is possible when
.FEATURE pc_assignment
is used. Note: You should not use
assignments to *
, use
.ORG
instead.
.ASIZE
Reading this pseudo variable will return the current size of the Accumulator in bits.
For the 65816 instruction set .ASIZE will return either 8 or 16, depending on the current size of the operand in immediate accu addressing mode.
For all other CPU instruction sets, .ASIZE will always return 8.
Example:
; Reverse Subtract with Accumulator
; A = memory - A
.macro rsb param
.if .asize = 8
eor #$ff
.else
eor #$ffff
.endif
sec
adc param
.endmacro
See also:
.ISIZE
.CPU
Reading this pseudo variable will give a constant integer value that
tells which CPU is currently enabled. It can also tell which instruction
set the CPU is able to translate. The value read from the pseudo variable
should be further examined by using one of the constants defined by the
"cpu" macro package (see
.MACPACK
).
It may be used to replace the .IFPxx pseudo instructions or to construct even more complex expressions.
Example:
.macpack cpu
.if (.cpu .bitand CPU_ISET_65816)
phx
phy
.else
txa
pha
tya
pha
.endif
.ISIZE
Reading this pseudo variable will return the current size of the Index register in bits.
For the 65816 instruction set .ISIZE will return either 8 or 16, depending on the current size of the operand in immediate index addressing mode.
For all other CPU instruction sets, .ISIZE will always return 8.
See also:
.ASIZE
.PARAMCOUNT
This builtin pseudo variable is only available in macros. It is replaced by the actual number of parameters that were given in the macro invocation.
Example:
.macro foo arg1, arg2, arg3
.if .paramcount <> 3
.error "Too few parameters for macro foo"
.endif
...
.endmacro
See section Macros.
.TIME
Reading this pseudo variable will give a constant integer value that represents the current time in POSIX standard (as seconds since the Epoch).
It may be used to encode the time of translation somewhere in the created code.
Example:
.dword .time ; Place time here
.VERSION
Reading this pseudo variable will give the assembler version according to the following formula:
VER_MAJOR*$100 + VER_MINOR*$10
It may be used to encode the assembler version or check the assembler for special features not available with older versions.
Example:
Version 2.14 of the assembler will return $2E0 as numerical constant when
reading the pseudo variable .VERSION
.
Pseudo functions expect their arguments in parenthesis, and they have a result, either a string or an expression.
.ADDRSIZE
The .ADDRSIZE
function is used to return the interal address size
associated with a symbol. This can be helpful in macros when knowing the address
size of symbol can help with custom instructions.
Example:
.macro myLDA foo
.if .ADDRSIZE(foo) = 1
;do custom command based on zeropage addressing:
.byte 0A5h, foo
.elseif .ADDRSIZE(foo) = 2
;do custom command based on absolute addressing:
.byte 0ADh
.word foo
.elseif .ADDRSIZE(foo) = 0
; no address size defined for this symbol:
.out .sprintf("Error, address size unknown for symbol %s", .string(foo))
.endif
.endmacro
This command is new and must be enabled with the .FEATURE addrsize
command.
See:
.FEATURE
.BANK
The .BANK
function is used to support systems with banked memory. The
argument is an expression with exactly one segment reference - usually a
label. The function result is the value of the bank
attribute assigned
to the run memory area of the segment. Please see the linker documentation
for more information about memory areas and their attributes.
The value of .BANK
can be used to switch memory so that a memory bank
containing specific data is available.
The bank
attribute is a 32 bit integer and so is the result of the
.BANK
function. You will have to use
.LOBYTE
or similar functions to address just part of it.
Please note that .BANK
will always get evaluated in the link stage, so
an expression containing .BANK
can never be used where a constant known
result is expected (for example with .RES
).
Example:
.segment "BANK1"
.proc banked_func_1
...
.endproc
.segment "BANK2"
.proc banked_func_2
...
.endproc
.proc bank_table
.addr banked_func_1
.byte <.BANK (banked_func_1)
.addr banked_func_2
.byte <.BANK (banked_func_2)
.endproc
.BANKBYTE
The function returns the bank byte (that is, bits 16-23) of its argument. It works identical to the '^' operator.
.BLANK
Builtin function. The function evaluates its argument in braces and yields "false" if the argument is non blank (there is an argument), and "true" if there is no argument. The token list that makes up the function argument may optionally be enclosed in curly braces. This allows the inclusion of tokens that would otherwise terminate the list (the closing right parenthesis). The curly braces are not considered part of the list, a list just consisting of curly braces is considered to be empty.
As an example, the .IFBLANK
statement may be replaced by
.if .blank({arg})
.CONCAT
Builtin string function. The function allows to concatenate a list of string
constants separated by commas. The result is a string constant that is the
concatenation of all arguments. This function is most useful in macros and
when used together with the .STRING
builtin function. The function may
be used in any case where a string constant is expected.
Example:
.include .concat ("myheader", ".", "inc")
This is the same as the command
.include "myheader.inc"
.CONST
Builtin function. The function evaluates its argument in braces and yields "true" if the argument is a constant expression (that is, an expression that yields a constant value at assembly time) and "false" otherwise. As an example, the .IFCONST statement may be replaced by
.if .const(a + 3)
.HIBYTE
The function returns the high byte (that is, bits 8-15) of its argument. It works identical to the '>' operator.
.HIWORD
The function returns the high word (that is, bits 16-31) of its argument.
See:
.LOWORD
.IDENT
The function expects a string as its argument, and converts this argument
into an identifier. If the string starts with the current
.LOCALCHAR
, it will be converted into a cheap local
identifier, otherwise it will be converted into a normal identifier.
Example:
.macro makelabel arg1, arg2
.ident (.concat (arg1, arg2)):
.endmacro
makelabel "foo", "bar"
.word foobar ; Valid label
.LEFT
Builtin function. Extracts the left part of a given token list.
Syntax:
.LEFT (<int expr>, <token list>)
The first integer expression gives the number of tokens to extract from the token list. The second argument is the token list itself. The token list may optionally be enclosed into curly braces. This allows the inclusion of tokens that would otherwise terminate the list (the closing right paren in the given case).
Example:
To check in a macro if the given argument has a '#' as first token (immediate addressing mode), use something like this:
.macro ldax arg
...
.if (.match (.left (1, {arg}), #))
; ldax called with immediate operand
...
.endif
...
.endmacro
See also the
.MID
and
.RIGHT
builtin functions.
.LOBYTE
The function returns the low byte (that is, bits 0-7) of its argument. It works identical to the '<' operator.
.LOWORD
The function returns the low word (that is, bits 0-15) of its argument.
See:
.HIWORD
.MATCH
Builtin function. Matches two token lists against each other. This is most useful within macros, since macros are not stored as strings, but as lists of tokens.
The syntax is
.MATCH(<token list #1>, <token list #2>)
Both token list may contain arbitrary tokens with the exception of the terminator token (comma resp. right parenthesis) and
The token lists may optionally be enclosed into curly braces. This allows the inclusion of tokens that would otherwise terminate the list (the closing right paren in the given case). Often a macro parameter is used for any of the token lists.
Please note that the function does only compare tokens, not token
attributes. So any number is equal to any other number, regardless of the
actual value. The same is true for strings. If you need to compare tokens
and token attributes, use the
.XMATCH
function.
Example:
Assume the macro ASR
, that will shift right the accumulator by one,
while honoring the sign bit. The builtin processor instructions will allow
an optional "A" for accu addressing for instructions like ROL
and
ROR
. We will use the
.MATCH
function
to check for this and print and error for invalid calls.
.macro asr arg
.if (.not .blank(arg)) .and (.not .match ({arg}, a))
.error "Syntax error"
.endif
cmp #$80 ; Bit 7 into carry
lsr a ; Shift carry into bit 7
.endmacro
The macro will only accept no arguments, or one argument that must be the reserved keyword "A".
See:
.XMATCH
.MAX
Builtin function. The result is the larger of two values.
The syntax is
.MAX (<value #1>, <value #2>)
Example:
; Reserve space for the larger of two data blocks
savearea: .res .max (.sizeof (foo), .sizeof (bar))
See:
.MIN
.MID
Builtin function. Takes a starting index, a count and a token list as arguments. Will return part of the token list.
Syntax:
.MID (<int expr>, <int expr>, <token list>)
The first integer expression gives the starting token in the list (the first token has index 0). The second integer expression gives the number of tokens to extract from the token list. The third argument is the token list itself. The token list may optionally be enclosed into curly braces. This allows the inclusion of tokens that would otherwise terminate the list (the closing right paren in the given case).
Example:
To check in a macro if the given argument has a '#
' as first token
(immediate addressing mode), use something like this:
.macro ldax arg
...
.if (.match (.mid (0, 1, {arg}), #))
; ldax called with immediate operand
...
.endif
...
.endmacro
See also the
.LEFT
and
.RIGHT
builtin functions.
.MIN
Builtin function. The result is the smaller of two values.
The syntax is
.MIN (<value #1>, <value #2>)
Example:
; Reserve space for some data, but 256 bytes maximum
savearea: .res .min (.sizeof (foo), 256)
See:
.MAX
.REF, .REFERENCED
Builtin function. The function expects an identifier as argument in braces.
The argument is evaluated, and the function yields "true" if the identifier
is a symbol that has already been referenced somewhere in the source file up
to the current position. Otherwise the function yields false. As an example,
the
.IFREF
statement may be replaced by
.if .referenced(a)
See:
.DEFINED
.RIGHT
Builtin function. Extracts the right part of a given token list.
Syntax:
.RIGHT (<int expr>, <token list>)
The first integer expression gives the number of tokens to extract from the token list. The second argument is the token list itself. The token list may optionally be enclosed into curly braces. This allows the inclusion of tokens that would otherwise terminate the list (the closing right paren in the given case).
See also the
.LEFT
and
.MID
builtin functions.
.SIZEOF
.SIZEOF()
is a pseudo function that returns the size of its argument.
The argument can be a struct/union, a struct member, a scope/procedure, or a
label. In the case of a procedure or label, its size is defined by the
amount of data placed in the segment where the label is relative to. If a
line of code switches segments (for example, in a macro), data placed in
other segments does not count for the size.
Please note that a symbol or scope must exist before it can be used together
with .SIZEOF()
(that may get relaxed later, but always will be true for
scopes). A scope has preference over a symbol with the same name; so, if the
last part of a name represents both a scope and a symbol, then the scope is
chosen over the symbol.
After the following code:
.struct Point ; Struct size = 4
xcoord .word
ycoord .word
.endstruct
P: .tag Point ; Declare a point
@P: .tag Point ; Declare another point
.code
.proc Code
nop
.proc Inner
nop
.endproc
nop
.endproc
.proc Data
.data ; Segment switch!!!
.res 4
.endproc
.sizeof(Point)
will have the value 4, because this is the size of struct Point
.
.sizeof(Point::xcoord)
will have the value 2, because this is the size of the member xcoord
in struct Point
.
.sizeof(P)
will have the value 4, this is the size of the data declared on the same
source line as the label P
, which is in the same segment that P
is relative to.
.sizeof(@P)
will have the value 4, see above. The example demonstrates that .SIZEOF
does also work for cheap local symbols.
.sizeof(Code)
will have the value 3, since this is amount of data emitted into the code
segment, the segment that was active when Code
was entered. Note that
this value includes the amount of data emitted in child scopes (in this
case Code::Inner
).
.sizeof(Code::Inner)
will have the value 1 as expected.
.sizeof(Data)
will have the value 0. Data is emitted within the scope Data
, but since
the segment is switched after entry, this data is emitted into another
segment.
.STRAT
Builtin function. The function accepts a string and an index as arguments and returns the value of the character at the given position as an integer value. The index is zero based.
Example:
.macro M Arg
; Check if the argument string starts with '#'
.if (.strat (Arg, 0) = '#')
...
.endif
.endmacro
.SPRINTF
Builtin function. It expects a format string as first argument. The number
and type of the following arguments depend on the format string. The format
string is similar to the one of the C printf
function. Missing things
are: Length modifiers, variable width.
The result of the function is a string.
Example:
num = 3
; Generate an identifier:
.ident (.sprintf ("%s%03d", "label", num)):
.STRING
Builtin function. The function accepts an argument in braces and converts this argument into a string constant. The argument may be an identifier, or a constant numeric value.
Since you can use a string in the first place, the use of the function may not be obvious. However, it is useful in macros, or more complex setups.
Example:
; Emulate other assemblers:
.macro section name
.segment .string(name)
.endmacro
.STRLEN
Builtin function. The function accepts a string argument in braces and evaluates to the length of the string.
Example:
The following macro encodes a string as a pascal style string with a leading length byte.
.macro PString Arg
.byte .strlen(Arg), Arg
.endmacro
.TCOUNT
Builtin function. The function accepts a token list in braces. The function result is the number of tokens given as argument. The token list may optionally be enclosed into curly braces which are not considered part of the list and not counted. Enclosement in curly braces allows the inclusion of tokens that would otherwise terminate the list (the closing right paren in the given case).
Example:
The ldax
macro accepts the '#' token to denote immediate addressing (as
with the normal 6502 instructions). To translate it into two separate 8 bit
load instructions, the '#' token has to get stripped from the argument:
.macro ldax arg
.if (.match (.mid (0, 1, {arg}), #))
; ldax called with immediate operand
lda #<(.right (.tcount ({arg})-1, {arg}))
ldx #>(.right (.tcount ({arg})-1, {arg}))
.else
...
.endif
.endmacro
.XMATCH
Builtin function. Matches two token lists against each other. This is most useful within macros, since macros are not stored as strings, but as lists of tokens.
The syntax is
.XMATCH(<token list #1>, <token list #2>)
Both token list may contain arbitrary tokens with the exception of the terminator token (comma resp. right parenthesis) and
The token lists may optionally be enclosed into curly braces. This allows the inclusion of tokens that would otherwise terminate the list (the closing right paren in the given case). Often a macro parameter is used for any of the token lists.
The function compares tokens and token values. If you need a function
that just compares the type of tokens, have a look at the
.MATCH
function.
See:
.MATCH
Here's a list of all control commands and a description, what they do:
.A16
Valid only in 65816 mode. Switch the accumulator to 16 bit.
Note: This command will not emit any code, it will tell the assembler to create 16 bit operands for immediate accumulator addressing mode.
See also:
.SMART
.A8
Valid only in 65816 mode. Switch the accumulator to 8 bit.
Note: This command will not emit any code, it will tell the assembler to create 8 bit operands for immediate accu addressing mode.
See also:
.SMART
.ADDR
Define word sized data. In 6502 mode, this is an alias for .WORD
and
may be used for better readability if the data words are address values. In
65816 mode, the address is forced to be 16 bit wide to fit into the current
segment. See also
.FARADDR
. The command
must be followed by a sequence of (not necessarily constant) expressions.
Example:
.addr $0D00, $AF13, _Clear
.ALIGN
Align data to a given boundary. The command expects a constant integer argument in the range 1 ... 65536, plus an optional second argument in byte range. If there is a second argument, it is used as fill value, otherwise the value defined in the linker configuration file is used (the default for this value is zero).
.ALIGN
will insert fill bytes, and the number of fill bytes depend of
the final address of the segment. .ALIGN
cannot insert a variable
number of bytes, since that would break address calculations within the
module. So each .ALIGN
expects the segment to be aligned to a multiple
of the alignment, because that allows the number of fill bytes to be
calculated in advance by the assembler. You are therefore required to
specify a matching alignment for the segment in the linker config. The
linker will output a warning if the alignment of the segment is less than
what is necessary to have a correct alignment in the object file.
Example:
.align 256
Some unexpected behaviour might occur if there are multiple .ALIGN
commands with different arguments. To allow the assembler to calculate the
number of fill bytes in advance, the alignment of the segment must be a
multiple of each of the alignment factors. This may result in unexpectedly
large alignments for the segment within the module.
Example:
.align 15
.byte 15
.align 18
.byte 18
For the assembler to be able to align correctly, the segment must be aligned to the least common multiple of 15 and 18 which is 90. The assembler will calculate this automatically and will mark the segment with this value.
Unfortunately, the combined alignment may get rather large without the user knowing about it, wasting space in the final executable. If we add another alignment to the example above
.align 15
.byte 15
.align 18
.byte 18
.align 251
.byte 0
the assembler will force a segment alignment to the least common multiple of
15, 18 and 251 - which is 22590. To protect the user against errors, the
assembler will issue a warning when the combined alignment exceeds 256. The
command line option
--large-alignment
will disable this warning.
Please note that with alignments that are a power of two (which were the only alignments possible in older versions of the assembler), the problem is less severe, because the least common multiple of powers to the same base is always the larger one.
.ASCIIZ
Define a string with a trailing zero.
Example:
Msg: .asciiz "Hello world"
This will put the string "Hello world" followed by a binary zero into the current segment. There may be more strings separated by commas, but the binary zero is only appended once (after the last one).
.ASSERT
Add an assertion. The command is followed by an expression, an action
specifier, and an optional message that is output in case the assertion
fails. If no message was given, the string "Assertion failed" is used. The
action specifier may be one of warning
, error
, ldwarning
or
lderror
. In the former two cases, the assertion is evaluated by the
assembler if possible, and in any case, it's also passed to the linker in
the object file (if one is generated). The linker will then evaluate the
expression when segment placement has been done.
Example:
.assert * = $8000, error, "Code not at $8000"
The example assertion will check that the current location is at $8000,
when the output file is written, and abort with an error if this is not
the case.  The action specifier
warning
outputs a warning, while the error
specifier outputs
an error message. In the latter case, generation of the output file is
suppressed in both the assembler and linker.
.AUTOIMPORT
Is followed by a plus or a minus character. When switched on (using a +), undefined symbols are automatically marked as import instead of giving errors. When switched off (which is the default so this does not make much sense), this does not happen and an error message is displayed. The state of the autoimport flag is evaluated when the complete source was translated, before outputting actual code, so it is not possible to switch this feature on or off for separate sections of code. The last setting is used for all symbols.
You should probably not use this switch because it delays error messages about undefined symbols until the link stage. The cc65 compiler (which is supposed to produce correct assembler code in all circumstances, something which is not true for most assembler programmers) will insert this command to avoid importing each and every routine from the runtime library.
Example:
.autoimport + ; Switch on auto import
.BANKBYTES
Define byte sized data by extracting only the bank byte (that is, bits 16-23) from
each expression. This is equivalent to
.BYTE
with
the operator '^' prepended to each expression in its list.
Example:
.define MyTable TableItem0, TableItem1, TableItem2, TableItem3
TableLookupLo: .lobytes MyTable
TableLookupHi: .hibytes MyTable
TableLookupBank: .bankbytes MyTable
which is equivalent to
TableLookupLo: .byte <TableItem0, <TableItem1, <TableItem2, <TableItem3
TableLookupHi: .byte >TableItem0, >TableItem1, >TableItem2, >TableItem3
TableLookupBank: .byte ^TableItem0, ^TableItem1, ^TableItem2, ^TableItem3
See also:
.BYTE
,
.HIBYTES
,
.LOBYTES
.BSS
Switch to the BSS segment. The name of the BSS segment is always "BSS", so this is a shortcut for
.segment "BSS"
See also the
.SEGMENT
command.
.BYT, .BYTE
Define byte sized data. Must be followed by a sequence of (byte ranged) expressions or strings.
Example:
.byte "Hello "
.byt "world", $0D, $00
.CASE
Switch on or off case sensitivity on identifiers. The default is off (that is, identifiers are case sensitive), but may be changed by the -i switch on the command line. The command must be followed by a '+' or '-' character to switch the option on or off respectively.
Example:
.case - ; Identifiers are not case sensitive
.CHARMAP
Apply a custom mapping for characters. The command is followed by two
numbers. The first one is the index of the source character (range 0..255);
the second one is the mapping (range 0..255). The mapping applies to all
character and string constants when they generate output; and, overrides
a mapping table specified with the
-t
command line switch.
Example:
.charmap $41, $61 ; Map 'A' to 'a'
.CODE
Switch to the CODE segment. The name of the CODE segment is always "CODE", so this is a shortcut for
.segment "CODE"
See also the
.SEGMENT
command.
.CONDES
Export a symbol and mark it in a special way. The linker is able to build tables of all such symbols. This may be used to automatically create a list of functions needed to initialize linked library modules.
Note: The linker has a feature to build a table of marked routines, but it
is your code that must call these routines, so just declaring a symbol with
.CONDES
does nothing by itself.
All symbols are exported as an absolute (16 bit) symbol. You don't need to
use an additional
.EXPORT
statement, this
is implied by .CONDES
.
.CONDES
is followed by the type, which may be constructor
,
destructor
or a numeric value between 0 and 6 (where 0 is the same as
specifying constructor
and 1 is equal to specifying destructor
).
The
.CONSTRUCTOR
,
.DESTRUCTOR
and
.INTERRUPTOR
commands are actually shortcuts for .CONDES
with a type of constructor
resp. destructor
or interruptor
.
After the type, an optional priority may be specified. Higher numeric values mean higher priority. If no priority is given, the default priority of 7 is used. Be careful when assigning priorities to your own module constructors so they won't interfere with the ones in the cc65 library.
Example:
.condes ModuleInit, constructor
.condes ModInit, 0, 16
See the
.CONSTRUCTOR
,
.DESTRUCTOR
and
.INTERRUPTOR
commands and the separate section
Module constructors/destructors explaining the feature in more
detail.
.CONSTRUCTOR
Export a symbol and mark it as a module constructor. This may be used together with the linker to build a table of constructor subroutines that are called by the startup code.
Note: The linker has a feature to build a table of marked routines, but it is your code that must call these routines, so just declaring a symbol as constructor does nothing by itself.
A constructor is always exported as an absolute (16 bit) symbol. You don't
need to use an additional .export
statement, this is implied by
.constructor
. It may have an optional priority that is separated by a
comma. Higher numeric values mean a higher priority. If no priority is
given, the default priority of 7 is used. Be careful when assigning
priorities to your own module constructors so they won't interfere with the
ones in the cc65 library.
Example:
.constructor ModuleInit
.constructor ModInit, 16
See the
.CONDES
and
.DESTRUCTOR
commands and the separate section
Module constructors/destructors explaining the
feature in more detail.
.DATA
Switch to the DATA segment. The name of the DATA segment is always "DATA", so this is a shortcut for
.segment "DATA"
See also the
.SEGMENT
command.
.DBYT
Define word sized data with the hi and lo bytes swapped (use .WORD
to
create word sized data in native 65XX format). Must be followed by a
sequence of (word ranged) expressions.
Example:
.dbyt $1234, $4512
This will emit the bytes
$12 $34 $45 $12
into the current segment in that order.
.DEBUGINFO
Switch on or off debug info generation. The default is off (that is, the object file will not contain debug infos), but may be changed by the -g switch on the command line. The command must be followed by a '+' or '-' character to switch the option on or off respectively.
Example:
.debuginfo + ; Generate debug info
.DEFINE
Start a define style macro definition. The command is followed by an identifier (the macro name) and optionally by a list of formal arguments in braces.
Please note that .DEFINE
shares most disadvantages with its C
counterpart, so the general advice is, NOT do use .DEFINE
if you
don't have to.
See also the
.UNDEFINE
command and
section
Macros.
.DELMAC, .DELMACRO
Delete a classic macro (defined with
.MACRO
) . The command is followed by the name of an
existing macro. Its definition will be deleted together with the name.
If necessary, another macro with this name may be defined later.
See:
.ENDMACRO
,
.EXITMACRO
,
.MACRO
See also section Macros.
.DEF, .DEFINED
Builtin function. The function expects an identifier as argument in braces.
The argument is evaluated, and the function yields "true" if the identifier
is a symbol that is already defined somewhere in the source file up to the
current position. Otherwise the function yields false. As an example, the
.IFDEF
statement may be replaced by
.if .defined(a)
.DEFINEDMACRO
Builtin function. The function expects an identifier as argument in braces. The argument is evaluated, and the function yields "true" if the identifier has already been defined as the name of a macro. Otherwise the function yields false. Example:
.macro add foo
clc
adc foo
.endmacro
.if .definedmacro(add)
add #$01
.else
clc
adc #$01
.endif
.DESTRUCTOR
Export a symbol and mark it as a module destructor. This may be used together with the linker to build a table of destructor subroutines that are called by the startup code.
Note: The linker has a feature to build a table of marked routines, but it is your code that must call these routines, so just declaring a symbol as constructor does nothing by itself.
A destructor is always exported as an absolute (16 bit) symbol. You don't
need to use an additional .export
statement, this is implied by
.destructor
. It may have an optional priority that is separated by a
comma. Higher numerical values mean a higher priority. If no priority is
given, the default priority of 7 is used. Be careful when assigning
priorities to your own module destructors so they won't interfere with the
ones in the cc65 library.
Example:
.destructor ModuleDone
.destructor ModDone, 16
See the
.CONDES
and
.CONSTRUCTOR
commands and the separate
section
Module constructors/destructors explaining
the feature in more detail.
.DWORD
Define dword sized data (4 bytes) Must be followed by a sequence of expressions.
Example:
.dword $12344512, $12FA489
.ELSE
Conditional assembly: Reverse the current condition.
.ELSEIF
Conditional assembly: Reverse current condition and test a new one.
.END
Forced end of assembly. Assembly stops at this point, even if the command is read from an include file.
.ENDENUM
End a
.ENUM
declaration.
.ENDIF
Conditional assembly: Close a
.IF...
or
.ELSE
branch.
.ENDMAC, .ENDMACRO
Marks the end of a macro definition.
See:
.DELMACRO
,
.EXITMACRO
,
.MACRO
See also section Macros.
.ENDPROC
End of the local lexical level (see
.PROC
).
.ENDREP, .ENDREPEAT
End a
.REPEAT
block.
.ENDSCOPE
End of the local lexical level (see
.SCOPE
).
.ENDSTRUCT
Ends a struct definition. See the
.STRUCT
command and the separate section named
"Structs and unions".
.ENDUNION
Ends a union definition. See the
.UNION
command and the separate section named
"Structs and unions".
.ENUM
Start an enumeration. This directive is very similar to the C enum
keyword. If a name is given, a new scope is created for the enumeration,
otherwise the enumeration members are placed in the enclosing scope.
In the enumeration body, symbols are declared. The first symbol has a value of zero, and each following symbol will get the value of the preceding, plus one. That behaviour may be overridden by an explicit assignment. Two symbols may have the same value.
Example:
.enum errorcodes
no_error
file_error
parse_error
.endenum
The above example will create a new scope named errorcodes
with three
symbols in it that get the values 0, 1, and 2 respectively. Another way
to write that would have been:
.scope errorcodes
no_error = 0
file_error = 1
parse_error = 2
.endscope
Please note that explicit scoping must be used to access the identifiers:
.word errorcodes::no_error
A more complex example:
.enum
EUNKNOWN = -1
EOK
EFILE
EBUSY
EAGAIN
EWOULDBLOCK = EAGAIN
.endenum
In that example, the enumeration does not have a name, which means that the
members will be visible in the enclosing scope, and can be used in that scope
without explicit scoping. The first member (EUNKNOWN
) has the value -1.
The values for the following members are incremented by one; so, EOK
would be zero, and so on. EWOULDBLOCK
is an alias for EAGAIN
; so,
it has an override for the value, using an already defined symbol.
.ERROR
Force an assembly error. The assembler will output an error message preceded by "User error". Assembly is continued but no object file will generated.
This command may be used to check for initial conditions that must be set before assembling a source file.
Example:
.if foo = 1
...
.elseif bar = 1
...
.else
.error "Must define foo or bar!"
.endif
See also:
.FATAL
,
.OUT
,
.WARNING
.EXITMAC, .EXITMACRO
Abort a macro expansion immediately. This command is often useful in recursive macros.
See:
.DELMACRO
,
.ENDMACRO
,
.MACRO
See also section Macros.
.EXPORT
Make symbols accessible from other modules. Must be followed by a comma separated list of symbols to export, with each one optionally followed by an address specification and (also optional) an assignment. Using an additional assignment in the export statement allows to define and export a symbol in one statement. The default is to export the symbol with the address size it actually has. The assembler will issue a warning, if the symbol is exported with an address size smaller than the actual address size.
Examples:
.export foo
.export bar: far
.export foobar: far = foo * bar
.export baz := foobar, zap: far = baz - bar
As with constant definitions, using :=
instead of =
marks the
symbols as a label.
See:
.EXPORTZP
.EXPORTZP
Make symbols accessible from other modules. Must be followed by a comma
separated list of symbols to export. The exported symbols are explicitly
marked as zero page symbols. An assignment may be included in the
.EXPORTZP
statement. This allows to define and export a symbol in one
statement.
Examples:
.exportzp foo, bar
.exportzp baz := $02
See:
.EXPORT
.FARADDR
Define far (24 bit) address data. The command must be followed by a sequence of (not necessarily constant) expressions.
Example:
.faraddr DrawCircle, DrawRectangle, DrawHexagon
See:
.ADDR
.FATAL
Force an assembly error and terminate assembly. The assembler will output an error message preceded by "User error" and will terminate assembly immediately.
This command may be used to check for initial conditions that must be set before assembling a source file.
Example:
.if foo = 1
...
.elseif bar = 1
...
.else
.fatal "Must define foo or bar!"
.endif
See also:
.ERROR
,
.OUT
,
.WARNING
.FEATURE
This directive may be used to enable one or more compatibility features
of the assembler. While the use of .FEATURE
should be avoided when
possible, it may be useful when porting sources written for other
assemblers. There is no way to switch a feature off, once you have
enabled it, so using
.FEATURE xxx
will enable the feature until end of assembly is reached.
The following features are available:
addrsize
Enables the .ADDRSIZE pseudo function. This function is experimental and not enabled by default.
See also:
.ADDRSIZE
at_in_identifiers
Accept the at character ('@') as a valid character in identifiers. The at character is not allowed to start an identifier, even with this feature enabled.
bracket_as_indirect
Use []
instead of ()
for the indirect addressing modes.
Example:
lda [$82]
lda [$82,x]
lda [$82],y
jmp [$fffe]
jmp [table,x]
Note: This should not be used in 65186 mode because it conflicts with
the 65816 instruction syntax for far addressing. See the section covering
address sizes
for more information.
c_comments
Allow C like comments using /*
and */
as left and right
comment terminators. Note that C comments may not be nested. There's also a
pitfall when using C like comments: All statements must be terminated by
"end-of-line". Using C like comments, it is possible to hide the newline,
which results in error messages. See the following non working example:
lda #$00 /* This comment hides the newline
*/ sta $82
dollar_in_identifiers
Accept the dollar sign ('$') as a valid character in identifiers. The dollar character is not allowed to start an identifier, even with this feature enabled.
dollar_is_pc
The dollar sign may be used as an alias for the star ('*'), which gives the value of the current PC in expressions. Note: Assignment to the pseudo variable is not allowed.
force_range
Force expressions into their valid range for immediate addressing and
storage operators like
.BYTE
and
.WORD
. Be very careful with this one,
since it will completely disable error checks.
labels_without_colons
Allow labels without a trailing colon. These labels are only accepted, if they start at the beginning of a line (no leading white space).
leading_dot_in_identifiers
Accept the dot ('.') as the first character of an identifier. This may be used for example to create macro names that start with a dot emulating control directives of other assemblers. Note however, that none of the reserved keywords built into the assembler, that starts with a dot, may be overridden. When using this feature, you may also get into trouble if later versions of the assembler define new keywords starting with a dot.
loose_char_term
Accept single quotes as well as double quotes as terminators for char constants.
loose_string_term
Accept single quotes as well as double quotes as terminators for string constants.
missing_char_term
Accept single quoted character constants where the terminating quote is missing.
lda #'a
Note: This does not work in conjunction with .FEATURE
loose_string_term
, since in this case the input would be ambiguous.
org_per_seg
This feature makes relocatable/absolute mode local to the current segment.
Using
.ORG
when org_per_seg
is in
effect will only enable absolute mode for the current segment. Dito for
.RELOC
.
pc_assignment
Allow assignments to the PC symbol ('*' or '$' if dollar_is_pc
is enabled). Such an assignment is handled identical to the
.ORG
command (which is usually not needed, so just
removing the lines with the assignments may also be an option when porting
code written for older assemblers).
string_escapes
Allow C-style backslash escapes within string constants to embed special characters. The following escapes are accepted:
\\
backslash ($5C
)\'
single quote ($27
)\"
double quote ($22
)\t
tab ($09
)\r
carriage return ($0D
)\n
newline ($0A
)\xNN
($NN
)Note that string escapes are converted to platform-specific characters in the same way that other characters are converted.
ubiquitous_idents
Allow the use of instructions names as names for macros and symbols. This makes it possible to "overload" instructions by defining a macro with the same name. This does also make it possible to introduce hard to find errors in your code, so be careful!
underline_in_numbers
Allow underlines within numeric constants. These may be used for grouping the digits of numbers for easier reading. Example:
.feature underline_in_numbers
.word %1100001110100101
.word %1100_0011_1010_0101 ; Identical but easier to read
It is also possible to specify features on the command line using the
--feature
command line option.
This is useful when translating sources written for older assemblers, when
you don't want to change the source code.
As an example, to translate sources written for Andre Fachats xa65 assembler, the features
labels_without_colons, pc_assignment, loose_char_term
may be helpful. They do not make ca65 completely compatible, so you may not be able to translate the sources without changes, even when enabling these features. However, I have found several sources that translate without problems when enabling these features on the command line.
.FILEOPT, .FOPT
Insert an option string into the object file. There are two forms of this command, one specifies the option by a keyword, the second specifies it as a number. Since usage of the second one needs knowledge of the internal encoding, its use is not recommended and I will only describe the first form here.
The command is followed by one of the keywords
author
comment
compiler
a comma and a string. The option is written into the object file together with the string value. This is currently unidirectional and there is no way to actually use these options once they are in the object file.
 The command is followed by a
comma separated list of symbols to import. The command is similar to
.IMPORT
, but the import reference is always
written to the generated object file, even if the symbol is never referenced
(
.IMPORT
will not generate import
references for unused symbols).
Example:
.forceimport needthisone, needthistoo
See:
.IMPORT
.GLOBAL
Declare symbols as global. Must be followed by a comma separated list of
symbols to declare. Symbols from the list, that are defined somewhere in the
source, are exported, all others are imported. Additional
.IMPORT
or
.EXPORT
commands for the same symbol are allowed.
Example:
.global foo, bar
.GLOBALZP
Declare symbols as global. Must be followed by a comma separated list of
symbols to declare. Symbols from the list, that are defined somewhere in the
source, are exported, all others are imported. Additional
.IMPORTZP
or
.EXPORTZP
commands for the same symbol are allowed. The symbols
in the list are explicitly marked as zero page symbols.
Example:
.globalzp foo, bar
.HIBYTES
Define byte sized data by extracting only the high byte (that is, bits 8-15) from
each expression. This is equivalent to
.BYTE
with
the operator '>' prepended to each expression in its list.
Example:
.lobytes $1234, $2345, $3456, $4567
.hibytes $fedc, $edcb, $dcba, $cba9
which is equivalent to
.byte $34, $45, $56, $67
.byte $fe, $ed, $dc, $cb
Example:
.define MyTable TableItem0, TableItem1, TableItem2, TableItem3
TableLookupLo: .lobytes MyTable
TableLookupHi: .hibytes MyTable
which is equivalent to
TableLookupLo: .byte <TableItem0, <TableItem1, <TableItem2, <TableItem3
TableLookupHi: .byte >TableItem0, >TableItem1, >TableItem2, >TableItem3
See also:
.BYTE
,
.LOBYTES
,
.BANKBYTES
.I16
Valid only in 65816 mode. Switch the index registers to 16 bit.
Note: This command will not emit any code, it will tell the assembler to create 16 bit operands for immediate operands.
See also the
.I8
and
.SMART
commands.
.I8
Valid only in 65816 mode. Switch the index registers to 8 bit.
Note: This command will not emit any code, it will tell the assembler to create 8 bit operands for immediate operands.
See also the
.I16
and
.SMART
commands.
.IF
Conditional assembly: Evaluate an expression and switch assembler output on or off depending on the expression. The expression must be a constant expression, that is, all operands must be defined.
A expression value of zero evaluates to FALSE, any other value evaluates to TRUE.
.IFBLANK
Conditional assembly: Check if there are any remaining tokens in this line,
and evaluate to FALSE if this is the case, and to TRUE otherwise. If the
condition is not true, further lines are not assembled until an
.ELSE
,
.ELSEIF
or
.ENDIF
directive.
This command is often used to check if a macro parameter was given. Since an empty macro parameter will evaluate to nothing, the condition will evaluate to TRUE if an empty parameter was given.
Example:
.macro arg1, arg2
.ifblank arg2
lda #arg1
.else
lda #arg2
.endif
.endmacro
See also:
.BLANK
.IFCONST
Conditional assembly: Evaluate an expression and switch assembler output on or off depending on the constness of the expression.
A const expression evaluates to to TRUE, a non const expression (one containing an imported or currently undefined symbol) evaluates to FALSE.
See also:
.CONST
.IFDEF
Conditional assembly: Check if a symbol is defined. Must be followed by a symbol name. The condition is true if the the given symbol is already defined, and false otherwise.
See also:
.DEFINED
.IFNBLANK
Conditional assembly: Check if there are any remaining tokens in this line,
and evaluate to TRUE if this is the case, and to FALSE otherwise. If the
condition is not true, further lines are not assembled until an
.ELSE
,
.ELSEIF
or
.ENDIF
directive.
This command is often used to check if a macro parameter was given. Since an empty macro parameter will evaluate to nothing, the condition will evaluate to FALSE if an empty parameter was given.
Example:
.macro arg1, arg2
lda #arg1
.ifnblank arg2
lda #arg2
.endif
.endmacro
See also:
.BLANK
.IFNDEF
Conditional assembly: Check if a symbol is defined. Must be followed by a symbol name. The condition is true if the the given symbol is not defined, and false otherwise.
See also:
.DEFINED
.IFNREF
Conditional assembly: Check if a symbol is referenced. Must be followed by a symbol name. The condition is true if if the the given symbol was not referenced before, and false otherwise.
See also:
.REFERENCED
.IFP02
Conditional assembly: Check if the assembler is currently in 6502 mode
(see
.P02
command).
.IFP4510
Conditional assembly: Check if the assembler is currently in 4510 mode
(see
.P4510
command).
.IFP816
Conditional assembly: Check if the assembler is currently in 65816 mode
(see
.P816
command).
.IFPC02
Conditional assembly: Check if the assembler is currently in 65C02 mode
(see
.PC02
command).
.IFPSC02
Conditional assembly: Check if the assembler is currently in 65SC02 mode
(see
.PSC02
command).
.IFREF
Conditional assembly: Check if a symbol is referenced. Must be followed by a symbol name. The condition is true if if the the given symbol was referenced before, and false otherwise.
This command may be used to build subroutine libraries in include files (you may use separate object modules for this purpose too).
Example:
.ifref ToHex ; If someone used this subroutine
ToHex: tay ; Define subroutine
lda HexTab,y
rts
.endif
See also:
.REFERENCED
.IMPORT
Import a symbol from another module. The command is followed by a comma separated list of symbols to import, with each one optionally followed by an address specification.
Example:
.import foo
.import bar: zeropage
See:
.IMPORTZP
.IMPORTZP
Import a symbol from another module. The command is followed by a comma separated list of symbols to import. The symbols are explicitly imported as zero page symbols (that is, symbols with values in byte range).
Example:
.importzp foo, bar
See:
.IMPORT
.INCBIN
Include a file as binary data. The command expects a string argument that is the name of a file to include literally in the current segment. In addition to that, a start offset and a size value may be specified, separated by commas. If no size is specified, all of the file from the start offset to end-of-file is used. If no start position is specified either, zero is assumed (which means that the whole file is inserted).
Example:
; Include whole file
.incbin "sprites.dat"
; Include file starting at offset 256
.incbin "music.dat", $100
; Read 100 bytes starting at offset 200
.incbin "graphics.dat", 200, 100
.INCLUDE
Include another file. Include files may be nested up to a depth of 16.
Example:
.include "subs.inc"
.INTERRUPTOR
Export a symbol and mark it as an interruptor. This may be used together with the linker to build a table of interruptor subroutines that are called in an interrupt.
Note: The linker has a feature to build a table of marked routines, but it is your code that must call these routines, so just declaring a symbol as interruptor does nothing by itself.
An interruptor is always exported as an absolute (16 bit) symbol. You don't
need to use an additional .export
statement, this is implied by
.interruptor
. It may have an optional priority that is separated by a
comma. Higher numeric values mean a higher priority. If no priority is
given, the default priority of 7 is used. Be careful when assigning
priorities to your own module constructors so they won't interfere with the
ones in the cc65 library.
Example:
.interruptor IrqHandler
.interruptor Handler, 16
See the
.CONDES
command and the separate
section
Module constructors/destructors explaining
the feature in more detail.
.ISMNEM, .ISMNEMONIC
Builtin function. The function expects an identifier as argument in braces. The argument is evaluated, and the function yields "true" if the identifier is defined as an instruction mnemonic that is recognized by the assembler. Example:
.if .not .ismnemonic(ina)
.macro ina
clc
adc #$01
.endmacro
.endif
.LINECONT
Switch on or off line continuations using the backslash character before a newline. The option is off by default. Note: Line continuations do not work in a comment. A backslash at the end of a comment is treated as part of the comment and does not trigger line continuation. The command must be followed by a '+' or '-' character to switch the option on or off respectively.
Example:
.linecont + ; Allow line continuations
lda \
#$20 ; This is legal now
.LIST
Enable output to the listing. The command must be followed by a boolean
switch ("on", "off", "+" or "-") and will enable or disable listing
output.
The option has no effect if the listing is not enabled by the command line
switch -l. If -l is used, an internal counter is set to 1. Lines are output
to the listing file, if the counter is greater than zero, and suppressed if
the counter is zero. Each use of .LIST
will increment or decrement the
counter.
Example:
.list on ; Enable listing output
.LISTBYTES
Set, how many bytes are shown in the listing for one source line. The default is 12, so the listing will show only the first 12 bytes for any source line that generates more than 12 bytes of code or data. The directive needs an argument, which is either "unlimited", or an integer constant in the range 4..255.
Examples:
.listbytes unlimited ; List all bytes
.listbytes 12 ; List the first 12 bytes
.incbin "data.bin" ; Include large binary file
.LOBYTES
Define byte sized data by extracting only the low byte (that is, bits 0-7) from
each expression. This is equivalent to
.BYTE
with
the operator '<' prepended to each expression in its list.
Example:
.lobytes $1234, $2345, $3456, $4567
.hibytes $fedc, $edcb, $dcba, $cba9
which is equivalent to
.byte $34, $45, $56, $67
.byte $fe, $ed, $dc, $cb
Example:
.define MyTable TableItem0, TableItem1, TableItem2, TableItem3
TableLookupLo: .lobytes MyTable
TableLookupHi: .hibytes MyTable
which is equivalent to
TableLookupLo: .byte <TableItem0, <TableItem1, <TableItem2, <TableItem3
TableLookupHi: .byte >TableItem0, >TableItem1, >TableItem2, >TableItem3
See also:
.BYTE
,
.HIBYTES
,
.BANKBYTES
.LOCAL
This command may only be used inside a macro definition. It declares a list of identifiers as local to the macro expansion.
A problem when using macros are labels: Since they don't change their name,
you get a "duplicate symbol" error if the macro is expanded the second time.
Labels declared with
.LOCAL
have their
name mapped to an internal unique name (___ABCD__
) with each macro
invocation.
Some other assemblers start a new lexical block inside a macro expansion.
This has some drawbacks however, since that will not allow any symbol
to be visible outside a macro, a feature that is sometimes useful. The
.LOCAL
command is in my eyes a better way
to address the problem.
You get an error when using
.LOCAL
outside
a macro.
.LOCALCHAR
Defines the character that start "cheap" local labels. You may use one of '@' and '?' as start character. The default is '@'.
Cheap local labels are labels that are visible only between two non
cheap labels. This way you can reuse identifiers like "loop
" without
using explicit lexical nesting.
Example:
.localchar '?'
Clear: lda #$00 ; Global label
?Loop: sta Mem,y ; Local label
dey
bne ?Loop ; Ok
rts
Sub: ... ; New global label
bne ?Loop ; ERROR: Unknown identifier!
.MACPACK
Insert a predefined macro package. The command is followed by an identifier specifying the macro package to insert. Available macro packages are:
atari Defines the scrcode macro.
cbm Defines the scrcode macro.
cpu Defines constants for the .CPU variable.
generic Defines generic macros like add, sub, and blt.
longbranch Defines conditional long-jump macros.
Including a macro package twice, or including a macro package that redefines already existing macros will lead to an error.
Example:
.macpack longbranch ; Include macro package
cmp #$20 ; Set condition codes
jne Label ; Jump long on condition
Macro packages are explained in more detail in section Macro packages.
.MAC, .MACRO
Start a classic macro definition. The command is followed by an identifier
(the macro name) and optionally by a comma separated list of identifiers
that are macro parameters. A macro definition is terminated by
.ENDMACRO
.
Example:
.macro ldax arg ; Define macro ldax
lda arg
ldx arg+1
See:
.DELMACRO
,
.ENDMACRO
,
.EXITMACRO
See also section Macros.
.ORG
Start a section of absolute code. The command is followed by a constant
expression that gives the new PC counter location for which the code is
assembled. Use
.RELOC
to switch back to
relocatable code.
By default, absolute/relocatable mode is global (valid even when switching
segments). Using .FEATURE
org_per_seg
it can be made segment local.
Please note that you do not need .ORG
in most cases. Placing
code at a specific address is the job of the linker, not the assembler, so
there is usually no reason to assemble code to a specific address.
Example:
.org $7FF ; Emit code starting at $7FF
.OUT
Output a string to the console without producing an error. This command
is similar to .ERROR
, however, it does not force an assembler error
that prevents the creation of an object file.
Example:
.out "This code was written by the codebuster(tm)"
See also:
.ERROR
,
.FATAL
,
.WARNING
.P02
Enable the 6502 instruction set, disable 65SC02, 65C02 and 65816
instructions. This is the default if not overridden by the
--cpu
command line option.
See:
.PC02
,
.PSC02
,
.P816
and
.P4510
.P4510
Enable the 4510 instruction set. This is a superset of the 65C02 and 6502 instruction sets.
See:
.P02
,
.PSC02
,
.PC02
and
.P816
.P816
Enable the 65816 instruction set. This is a superset of the 65SC02 and 6502 instruction sets.
See:
.P02
,
.PSC02
,
.PC02
and
.P4510
.PAGELEN, .PAGELENGTH
Set the page length for the listing. Must be followed by an integer
constant. The value may be "unlimited", or in the range 32 to 127. The
statement has no effect if no listing is generated. The default value is -1
(unlimited) but may be overridden by the --pagelength
command line
option. Beware: Since ca65 is a one pass assembler, the listing is generated
after assembly is complete, you cannot use multiple line lengths with one
source. Instead, the value set with the last .PAGELENGTH
is used.
Examples:
.pagelength 66 ; Use 66 lines per listing page
.pagelength unlimited ; Unlimited page length
.PC02
Enable the 65C02 instructions set. This instruction set includes all 6502 and 65SC02 instructions.
See:
.P02
,
.PSC02
,
.P816
and
.P4510
.POPCPU
Pop the last CPU setting from the stack, and activate it.
This command will switch back to the CPU that was last pushed onto the CPU
stack using the
.PUSHCPU
command, and
remove this entry from the stack.
The assembler will print an error message if the CPU stack is empty when this command is issued.
.POPSEG
Pop the last pushed segment from the stack, and set it.
This command will switch back to the segment that was last pushed onto the
segment stack using the
.PUSHSEG
command, and remove this entry from the stack.
The assembler will print an error message if the segment stack is empty when this command is issued.
See:
.PUSHSEG
.PROC
Start a nested lexical level with the given name and adds a symbol with this
name to the enclosing scope. All new symbols from now on are in the local
lexical level and are accessible from outside only via
explicit scope specification. Symbols defined outside this local
level may be accessed as long as their names are not used for new symbols
inside the level. Symbols names in other lexical levels do not clash, so you
may use the same names for identifiers. The lexical level ends when the
.ENDPROC
command is read. Lexical levels
may be nested up to a depth of 16 (this is an artificial limit to protect
against errors in the source).
Note: Macro names are always in the global level and in a separate name space. There is no special reason for this, it's just that I've never had any need for local macro definitions.
Example:
.proc Clear ; Define Clear subroutine, start new level
lda #$00
L1: sta Mem,y ; L1 is local and does not cause a
; duplicate symbol error if used in other
; places
dey
bne L1 ; Reference local symbol
rts
.endproc ; Leave lexical level
.PSC02
Enable the 65SC02 instructions set. This instruction set includes all 6502 instructions.
See:
.P02
,
.PC02
,
.P816
and
.P4510
.PUSHCPU
Push the currently active CPU onto a stack. The stack has a size of 8 entries.
.PUSHCPU
allows together with
.POPCPU
to switch to another CPU and to restore the old CPU
later, without knowledge of the current CPU setting.
The assembler will print an error message if the CPU stack is already full, when this command is issued.
.PUSHSEG
Push the currently active segment onto a stack. The entries on the stack include the name of the segment and the segment type. The stack has a size of 16 entries.
.PUSHSEG
allows together with
.POPSEG
to switch to another segment and to restore the old segment later, without
even knowing the name and type of the current segment.
The assembler will print an error message if the segment stack is already full, when this command is issued.
See:
.POPSEG
.RELOC
Switch back to relocatable mode. See the
.ORG
command.
.REPEAT
Repeat all commands between .REPEAT
and
.ENDREPEAT
constant number of times. The command is followed by
a constant expression that tells how many times the commands in the body
should get repeated. Optionally, a comma and an identifier may be specified.
If this identifier is found in the body of the repeat statement, it is
replaced by the current repeat count (starting with zero for the first time
the body is repeated).
.REPEAT
statements may be nested. If you use the same repeat count
identifier for a nested .REPEAT
statement, the one from the inner
level will be used, not the one from the outer level.
Example:
The following macro will emit a string that is "encrypted" in that all characters of the string are XORed by the value $55.
.macro Crypt Arg
.repeat .strlen(Arg), I
.byte .strat(Arg, I) ^ $55
.endrep
.endmacro
See:
.ENDREPEAT
.RES
Reserve storage. The command is followed by one or two constant expressions. The first one is mandatory and defines, how many bytes of storage should be defined. The second, optional expression must by a constant byte value that will be used as value of the data. If there is no fill value given, the linker will use the value defined in the linker configuration file (default: zero).
Example:
; Reserve 12 bytes of memory with value $AA
.res 12, $AA
.RODATA
Switch to the RODATA segment. The name of the RODATA segment is always "RODATA", so this is a shortcut for
.segment "RODATA"
The RODATA segment is a segment that is used by the compiler for readonly data like string constants.
See also the
.SEGMENT
command.
.SCOPE
Start a nested lexical level with the given name. All new symbols from now
on are in the local lexical level and are accessible from outside only via
explicit scope specification. Symbols defined
outside this local level may be accessed as long as their names are not used
for new symbols inside the level. Symbols names in other lexical levels do
not clash, so you may use the same names for identifiers. The lexical level
ends when the
.ENDSCOPE
command is
read. Lexical levels may be nested up to a depth of 16 (this is an
artificial limit to protect against errors in the source).
Note: Macro names are always in the global level and in a separate name space. There is no special reason for this, it's just that I've never had any need for local macro definitions.
Example:
.scope Error ; Start new scope named Error
None = 0 ; No error
File = 1 ; File error
Parse = 2 ; Parse error
.endscope ; Close lexical level
...
lda #Error::File ; Use symbol from scope Error
.SEGMENT
Switch to another segment. Code and data is always emitted into a segment, that is, a named section of data. The default segment is "CODE". There may be up to 254 different segments per object file (and up to 65534 per executable). There are shortcut commands for the most common segments ("ZEROPAGE", "CODE", "RODATA", "DATA", and "BSS").
The command is followed by a string containing the segment name (there are
some constraints for the name - as a rule of thumb use only those segment
names that would also be valid identifiers). There may also be an optional
address size separated by a colon. See the section covering
address sizes
for more information.
The default address size for a segment depends on the memory model specified on the command line. The default is "absolute", which means that you don't have to use an address size modifier in most cases.
"absolute" means that the is a segment with 16 bit (absolute) addressing. That is, the segment will reside somewhere in core memory outside the zero page. "zeropage" (8 bit) means that the segment will be placed in the zero page and direct (short) addressing is possible for data in this segment.
Beware: Only labels in a segment with the zeropage attribute are marked as reachable by short addressing. The '*' (PC counter) operator will work as in other segments and will create absolute variable values.
Please note that a segment cannot have two different address sizes. A segment specified as zeropage cannot be declared as being absolute later.
Examples:
.segment "ROM2" ; Switch to ROM2 segment
.segment "ZP2": zeropage ; New direct segment
.segment "ZP2" ; Ok, will use last attribute
.segment "ZP2": absolute ; Error, redecl mismatch
See:
.BSS
,
.CODE
,
.DATA
,
.RODATA
, and
.ZEROPAGE
.SET
.SET
is used to assign a value to a variable. See
Numeric variables for a full description.
.SETCPU
Switch the CPU instruction set. The command is followed by a string that
specifies the CPU. Possible values are those that can also be supplied to
the
--cpu
command line option,
namely: 6502, 6502X, 65SC02, 65C02, 65816, 4510 and HuC6280.
See:
.CPU
,
.IFP02
,
.IFP816
,
.IFPC02
,
.IFPSC02
,
.P02
,
.P816
,
.P4510
,
.PC02
,
.PSC02
.SMART
Switch on or off smart mode. The command must be followed by a '+' or '-' character to switch the option on or off respectively. The default is off (that is, the assembler doesn't try to be smart), but this default may be changed by the -s switch on the command line.
In smart mode the assembler will do the following:
REP
and SEP
instructions in 65816 mode
and update the operand sizes accordingly. If the operand of such an
instruction cannot be evaluated by the assembler (for example, because
the operand is an imported symbol), a warning is issued. Beware: Since
the assembler cannot trace the execution flow this may lead to false
results in some cases. If in doubt, use the .Inn
and .Ann
instructions to tell the assembler about the current settings.RTS
instruction by RTL
if it is
used within a procedure declared as far
, or if the procedure has
no explicit address specification, but it is far
because of the
memory model used.Example:
.smart ; Be smart
.smart - ; Stop being smart
.STRUCT
Starts a struct definition. Structs are covered in a separate section named "Structs and unions".
See also:
.ENDSTRUCT
,
.ENDUNION
,
.UNION
.TAG
Allocate space for a struct or union.
Example:
.struct Point
xcoord .word
ycoord .word
.endstruct
.bss
.tag Point ; Allocate 4 bytes
.UNDEF, .UNDEFINE
Delete a define style macro definition. The command is followed by an identifier which specifies the name of the macro to delete. Macro replacement is switched of when reading the token following the command (otherwise the macro name would be replaced by its replacement list).
See also the
.DEFINE
command and
section
Macros.
.UNION
Starts a union definition. Unions are covered in a separate section named "Structs and unions".
See also:
.ENDSTRUCT
,
.ENDUNION
,
.STRUCT
.WARNING
Force an assembly warning. The assembler will output a warning message
preceded by "User warning". This warning will always be output, even if
other warnings are disabled with the
-W0
command line option.
This command may be used to output possible problems when assembling the source file.
Example:
.macro jne target
.local L1
.ifndef target
.warning "Forward jump in jne, cannot optimize!"
beq L1
jmp target
L1:
.else
...
.endif
.endmacro
See also:
.ERROR
,
.FATAL
,
.OUT
.WORD
Define word sized data. Must be followed by a sequence of (word ranged, but not necessarily constant) expressions.
Example:
.word $0D00, $AF13, _Clear
.ZEROPAGE
Switch to the ZEROPAGE segment and mark it as direct (zeropage) segment. The name of the ZEROPAGE segment is always "ZEROPAGE", so this is a shortcut for
.segment "ZEROPAGE": zeropage
Because of the "zeropage" attribute, labels declared in this segment are addressed using direct addressing mode if possible. You must instruct the linker to place this segment somewhere in the address range 0..$FF otherwise you will get errors.
See:
.SEGMENT
Macros may be thought of as "parametrized super instructions". Macros are sequences of tokens that have a name. If that name is used in the source file, the macro is "expanded", that is, it is replaced by the tokens that were specified when the macro was defined.
In its simplest form, a macro does not have parameters. Here's an example:
.macro asr ; Arithmetic shift right
cmp #$80 ; Put bit 7 into carry
ror ; Rotate right with carry
.endmacro
The macro above consists of two real instructions, that are inserted into the code, whenever the macro is expanded. Macro expansion is simply done by using the name, like this:
lda $2010
asr
sta $2010
When using macro parameters, macros can be even more useful:
.macro inc16 addr
clc
lda addr
adc #<$0001
sta addr
lda addr+1
adc #>$0001
sta addr+1
.endmacro
When calling the macro, you may give a parameter, and each occurrence of the name "addr" in the macro definition will be replaced by the given parameter. So
inc16 $1000
will be expanded to
clc
lda $1000
adc #<$0001
sta $1000
lda $1000+1
adc #>$0001
sta $1000+1
A macro may have more than one parameter, in this case, the parameters are separated by commas. You are free to give less parameters than the macro actually takes in the definition. You may also leave intermediate parameters empty. Empty parameters are replaced by empty space (that is, they are removed when the macro is expanded). If you have a look at our macro definition above, you will see, that replacing the "addr" parameter by nothing will lead to wrong code in most lines. To help you, writing macros with a variable parameter list, there are some control commands:
.IFBLANK
tests the rest of the line and
returns true, if there are any tokens on the remainder of the line. Since
empty parameters are replaced by nothing, this may be used to test if a given
parameter is empty.
.IFNBLANK
tests the
opposite.
Look at this example:
.macro ldaxy a, x, y
.ifnblank a
lda #a
.endif
.ifnblank x
ldx #x
.endif
.ifnblank y
ldy #y
.endif
.endmacro
That macro may be called as follows:
ldaxy 1, 2, 3 ; Load all three registers
ldaxy 1, , 3 ; Load only a and y
ldaxy , , 3 ; Load y only
There's another helper command for determining which macro parameters are
valid:
.PARAMCOUNT
. That command is
replaced by the parameter count given, including explicitly empty
parameters:
ldaxy 1 ; .PARAMCOUNT = 1
ldaxy 1,,3 ; .PARAMCOUNT = 3
ldaxy 1,2 ; .PARAMCOUNT = 2
ldaxy 1, ; .PARAMCOUNT = 2
ldaxy 1,2,3 ; .PARAMCOUNT = 3
Macro parameters may optionally be enclosed into curly braces. This allows the inclusion of tokens that would otherwise terminate the parameter (the comma in case of a macro parameter).
.macro foo arg1, arg2
...
.endmacro
foo ($00,x) ; Two parameters passed
foo {($00,x)} ; One parameter passed
In the first case, the macro is called with two parameters: '($00
'
and 'x)
'. The comma is not passed to the macro, because it is part of the
calling sequence, not the parameters.
In the second case, '($00,x)
' is passed to the macro; this time,
including the comma.
Sometimes it is nice to write a macro that acts differently depending on the
type of the argument supplied. An example would be a macro that loads a 16 bit
value from either an immediate operand, or from memory. The
.MATCH
and
.XMATCH
functions will allow you to do exactly this:
.macro ldax arg
.if (.match (.left (1, {arg}), #))
; immediate mode
lda #<(.right (.tcount ({arg})-1, {arg}))
ldx #>(.right (.tcount ({arg})-1, {arg}))
.else
; assume absolute or zero page
lda arg
ldx 1+(arg)
.endif
.endmacro
Using the
.MATCH
function, the macro is able to
check if its argument begins with a hash mark.  Please note how the curly braces are used to enclose parameters to
pseudo functions handling token lists. This is necessary, because the token
lists may include commas or parens, which would be treated by the assembler
as end-of-list.
The macro can be used as
foo: .word $5678
...
ldax #$1234 ; X=$12, A=$34
...
ldax foo ; X=$56, A=$78
Macros may be used recursively:
.macro push r1, r2, r3
lda r1
pha
.ifnblank r2
push r2, r3
.endif
.endmacro
There's also a special macro command to help with writing recursive macros:
.EXITMACRO
. That command will stop macro
expansion immediately:
.macro push r1, r2, r3, r4, r5, r6, r7
.ifblank r1
; First parameter is empty
.exitmacro
.else
lda r1
pha
.endif
push r2, r3, r4, r5, r6, r7
.endmacro
When expanding that macro, the expansion will push all given parameters until an empty one is encountered. The macro may be called like this:
push $20, $21, $32 ; Push 3 ZP locations
push $21 ; Push one ZP location
Now, with recursive macros,
.IFBLANK
and
.PARAMCOUNT
, what else do you need?
Have a look at the inc16 macro above. Here is it again:
.macro inc16 addr
clc
lda addr
adc #<$0001
sta addr
lda addr+1
adc #>$0001
sta addr+1
.endmacro
If you have a closer look at the code, you will notice, that it could be written more efficiently, like this:
.macro inc16 addr
inc addr
bne Skip
inc addr+1
Skip:
.endmacro
But imagine what happens, if you use this macro twice? Since the label "Skip"
has the same name both times, you get a "duplicate symbol" error. Without a
way to circumvent this problem, macros are not as useful, as they could be.
One possible solution is the command
.LOCAL
.
It declares one or more symbols as local to the macro expansion. The names of
local variables are replaced by a unique name in each separate macro
expansion. So we can solve the problem above by using .LOCAL
:
.macro inc16 addr
.local Skip ; Make Skip a local symbol
inc addr
bne Skip
inc addr+1
Skip: ; Not visible outside
.endmacro
Another solution is of course to start a new lexical block inside the macro that hides any labels:
.macro inc16 addr
.proc
inc addr
bne Skip
inc addr+1
Skip:
.endproc
.endmacro
Starting with version 2.5 of the assembler, there is a second macro type
available: C style macros using the .DEFINE
directive. These macros are
similar to the classic macro type described above, but behaviour is sometimes
different:
.DEFINE
may not
span more than a line. You may use line continuation (see
.LINECONT
) to spread the definition over
more than one line for increased readability, but the macro itself
may not contain an end-of-line token.
.DEFINE
share
the name space with classic macros, but they are detected and replaced
at the scanner level. While classic macros may be used in every place,
where a mnemonic or other directive is allowed,
.DEFINE
style macros are allowed anywhere in a line. So
they are more versatile in some situations.
.DEFINE
style macros may take
parameters. While classic macros may have empty parameters, this is
not true for
.DEFINE
style macros.
For this macro type, the number of actual parameters must match
exactly the number of formal parameters.
To make this possible, formal parameters are enclosed in braces when
defining the macro. If there are no parameters, the empty braces may
be omitted.
.DEFINE
style macros may not
contain end-of-line tokens, there are things that cannot be done. They
may not contain several processor instructions for example. So, while
some things may be done with both macro types, each type has special
usages. The types complement each other.
Let's look at a few examples to make the advantages and disadvantages clear.
To emulate assemblers that use "EQU
" instead of "=
" you may use the
following .DEFINE
:
.define EQU =
foo EQU $1234 ; This is accepted now
You may use the directive to define string constants used elsewhere:
; Define the version number
.define VERSION "12.3a"
; ... and use it
.asciiz VERSION
Macros with parameters may also be useful:
.define DEBUG(message) .out message
DEBUG "Assembling include file #3"
Note that, while formal parameters have to be placed in parentheses, the actual argument used when invoking the macro should not be. The invoked arguments are separated by commas only, if parentheses are used by accident they will become part of the replaced token.
If you wish to have an expression follow the macro invocation, the last parameter can be enclosed in curly braces {} to indicate the end of that argument.
Examples:
.define COMBINE(ta,tb,tc) ta+tb*10+tc*100
.word COMBINE 5,6,7 ; 5+6*10+7*100 = 765
.word COMBINE(5,6,7) ; (5+6*10+7)*100 = 7200 ; incorrect use of parentheses
.word COMBINE 5,6,7+1 ; 5+6*10+7+1*100 = 172
.word COMBINE 5,6,{7}+1 ; 5+6*10+7*100+1 = 766 ; {} encloses the argument
.word COMBINE 5,6-2,7 ; 5+6-2*10+7*100 = 691
.word COMBINE 5,(6-2),7 ; 5+(6-2)*10+7*100 = 745
.word COMBINE 5,6,7+COMBINE 0,1,2 ; 5+6*10+7+0+1*10+2*100*100 = 20082
.word COMBINE 5,6,{7}+COMBINE 0,1,2 ; 5+6*10+7*100+0+1*10+2*100 = 975
With C macros it is common to enclose the results in parentheses to prevent unintended interactions with the text of the arguments, but additional care must be taken in this assembly context where parentheses may alter the meaning of a statement. In particular, indirect addressing modes may be accidentally implied:
.define DUO(ta,tb) (ta+(tb*10))
lda DUO(5,4), Y ; LDA (indirect), Y
lda 0+DUO(5,4), Y ; LDA absolute indexed, Y
When using the
-t option, characters are translated
into the target character set of the specific machine. However, this happens
as late as possible. This means that strings are translated if they are part
of a
.BYTE
or
.ASCIIZ
command. Characters are translated as soon as they are
used as part of an expression.
This behaviour is very intuitive outside of macros but may be confusing when doing more complex macros. If you compare characters against numeric values, be sure to take the translation into account.
Macros can be deleted. This will not work if the macro that should be deleted is currently expanded as in the following non-working example:
.macro notworking
.delmacro notworking
.endmacro
notworking ; Will not work
The commands to delete classic and define style macros differ. Classic macros
can be deleted by use of
.DELMACRO
, while
for
.DEFINE
style macros,
.UNDEFINE
must be used. Example:
.define value 1
.macro mac
.byte 2
.endmacro
.byte value ; Emit one byte with value 1
mac ; Emit another byte with value 2
.undefine value
.delmacro mac
.byte value ; Error: Unknown identifier
mac ; Error: Missing ":"
A separate command for .DEFINE
style macros was necessary, because
the name of such a macro is replaced by its replacement list on a very low
level. To get the actual name, macro replacement has to be switched off when
reading the argument to .UNDEFINE
. This does also mean that the
argument to .UNDEFINE
is not allowed to come from another
.DEFINE
. All this is not necessary for classic macros, so having two
different commands increases flexibility.
Using the
.MACPACK
directive, predefined
macro packages may be included with just one command. Available macro packages
are:
.MACPACK generic
This macro package defines macros that are useful in almost any program. Currently defined macros are:
.macro add Arg ; add without carry
clc
adc Arg
.endmacro
.macro sub Arg ; subtract without borrow
sec
sbc Arg
.endmacro
.macro bge Arg ; branch on greater-than or equal
bcs Arg
.endmacro
.macro blt Arg ; branch on less-than
bcc Arg
.endmacro
.macro bgt Arg ; branch on greater-than
.local L
beq L
bcs Arg
L:
.endmacro
.macro ble Arg ; branch on less-than or equal
beq Arg
bcc Arg
.endmacro
.macro bnz Arg ; branch on not zero
bne Arg
.endmacro
.macro bze Arg ; branch on zero
beq Arg
.endmacro
.MACPACK longbranch
This macro package defines long conditional jumps. They are named like the
short counterpart but with the 'b' replaced by a 'j'. Here is a sample
definition for the "jeq
" macro, the other macros are built using the same
scheme:
.macro jeq Target
.if .def(Target) .and ((*+2)-(Target) <= 127)
beq Target
.else
bne *+5
jmp Target
.endif
.endmacro
All macros expand to a short branch, if the label is already defined (back jump) and is reachable with a short jump. Otherwise the macro expands to a conditional branch with the branch condition inverted, followed by an absolute jump to the actual branch target.
The package defines the following macros:
jeq, jne, jmi, jpl, jcs, jcc, jvs, jvc
.MACPACK apple2
This macro package defines a macro named scrcode
. It takes a string
as argument and places this string into memory translated into screen codes.
.MACPACK atari
This macro package defines a macro named scrcode
. It takes a string
as argument and places this string into memory translated into screen codes.
.MACPACK cbm
This macro package defines a macro named scrcode
. It takes a string
as argument and places this string into memory translated into screen codes.
.MACPACK cpu
This macro package does not define any macros but constants used to examine
the value read from the
.CPU
pseudo variable. For
each supported CPU a constant similar to
CPU_6502
CPU_65SC02
CPU_65C02
CPU_65816
CPU_SWEET16
CPU_HUC6280
CPU_4510
is defined. These constants may be used to determine the exact type of the currently enabled CPU. In addition to that, for each CPU instruction set, another constant is defined:
CPU_ISET_6502
CPU_ISET_65SC02
CPU_ISET_65C02
CPU_ISET_65816
CPU_ISET_SWEET16
CPU_ISET_HUC6280
CPU_ISET_4510
The value read from the
.CPU
pseudo variable may
be checked with
.BITAND
to determine if the
currently enabled CPU supports a specific instruction set. For example the
65C02 supports all instructions of the 65SC02 CPU, so it has the
CPU_ISET_65SC02
bit set in addition to its native CPU_ISET_65C02
bit. Using
.if (.cpu .bitand CPU_ISET_65SC02)
lda (sp)
.else
ldy #$00
lda (sp),y
.endif
it is possible to determine if the
lda (sp)
instruction is supported, which is the case for the 65SC02, 65C02 and 65816 CPUs (the latter two are upwards compatible to the 65SC02).
.MACPACK module
This macro package defines a macro named module_header
. It takes an
identifier as argument and is used to define the header of a module both
in the dynamic and static variant.
For better orthogonality, the assembler defines similar symbols as the compiler, depending on the target system selected:
__APPLE2__
- Target system is apple2
or apple2enh
__APPLE2ENH__
- Target system is apple2enh
__ATARI2600__
- Target system is atari2600
__ATARI5200__
- Target system is atari5200
__ATARI__
- Target system is atari
or atarixl
__ATARIXL__
- Target system is atarixl
__ATMOS__
- Target system is atmos
__BBC__
- Target system is bbc
__C128__
- Target system is c128
__C16__
- Target system is c16
or plus4
__C64__
- Target system is c64
__CBM__
- Target is a Commodore or Commodore-alike system__CBM510__
- Target system is cbm510
__CBM610__
- Target system is cbm610
__CX16__
- Target system is cx16
__GEOS__
- Target is a GEOS system__GEOS_APPLE__
- Target system is geos-apple
__GEOS_CBM__
- Target system is geos-cbm
__LUNIX__
- Target system is lunix
__LYNX__
- Target system is lynx
__NES__
- Target system is nes
__OSIC1P__
- Target system is osic1p
__PET__
- Target system is pet
__PLUS4__
- Target system is plus4
__SIM6502__
- Target system is sim6502
__SIM65C02__
- Target system is sim65c02
__SUPERVISION__
- Target system is supervision
__VIC20__
- Target system is vic20
Structs and unions are special forms of scopes. They are, to some degree, comparable to their C counterparts. Both have a list of members. Each member allocates storage, and optionally may have a name whose value, in the case of a struct, usually is the storage offset from the beginning, and in the case of a union, doesn't change, and usually is zero.
Here is an example for a very simple struct with two members and a total size of 4 bytes:
.struct Point
xcoord .word
ycoord .word
.endstruct
A union shares the total space between all its members; its size is the same as that of the largest member. The offset of all members relative to the union is zero.
.union Entry
index .word
ptr .addr
.endunion
A struct or union may not necessarily have a name. If it is anonymous, no local scope is opened; the identifiers used to name the members are placed into the current scope instead.
A struct may contain unnamed members and definitions of local structs/unions. The storage allocators may contain a multiplier, as in the example below:
.struct Circle
.struct Point
.word 2 ; Allocate two words
.endstruct
Radius .word
.endstruct
The size of the Circle struct is 6 (three words).
Allocates multiples of 1 byte. .RES
requires an operand.
Allocates multiples of 2 bytes.
Allocates multiples of 3 bytes.
Allocates multiples of 4 bytes.
.ORG
keyword
The .ORG
keyword changes the offset value that is assigned to subsequent
member names. It's useful when using a struct to define the names of the
registers in an I/O chip. Example:
; 6551
.struct ACIA ; Asynchronous Communications Interface Adapter
.org $031C
DATA .byte
STATUS .byte
CMD .byte ; Command register
CTRL .byte ; Control register
.endstruct
lda ACIA::DATA ; Get an RS-232 character
.TAG
keyword
By using the .TAG keyword, it is possible to reserve space for an already defined struct or union within another struct:
.struct Point
xcoord .word
ycoord .word
.endstruct
.struct Circle
Origin .tag Point
Radius .byte
.endstruct
Actual space for a struct or union may be allocated by using the .TAG directive.
C: .tag Circle
Currently, members are just offsets from the start of the struct or union. To access a field of a struct, the member offset must be added to the address of the struct variable itself:
lda C+Circle::Radius ; Load circle radius into A
That may change in a future version of the assembler.
Structs and unions currently are implemented as nested symbol tables (in fact, they were a by-product of the improved scoping rules). Currently, the assembler has no idea of types. That means that the .TAG keyword only will allocate space. You won't be able to initialize variables declared with .TAG; and, adding an embedded structure to another structure with .TAG will not make that added structure accessible by using the '::' operator.
Note: This section applies mostly to C programs, so the explanation below uses examples from the C libraries. However, the feature may also be useful for assembler programs.
Using the
.CONSTRUCTOR
,
.DESTRUCTOR
and
.INTERRUPTOR
keywords it is possible to export functions in a
special way. The linker is able to generate tables with all functions of a
specific type. Such a table will only include symbols from object
files that are linked into a specific executable. This may be used to add
initialization and cleanup code for library modules, or a table of interrupt
handler functions.
The C heap functions are an example where module initialization code is used.
All heap functions (malloc
, free
, ...) work with a few
variables that contain the start and the end of the heap, pointers to the free
list and so on. Since the end of the heap depends on the size and start of the
stack, it must be initialized at runtime. However, initializing these
variables for programs that do not use the heap are a waste of time and
memory.
So the central module defines a function that contains initialization code and
exports this function using the .CONSTRUCTOR
statement. If (and only if)
this module is added to an executable by the linker, the initialization
function will be placed into the table of constructors by the linker. The C
startup code will call all constructors before main
and all destructors
after main
, so without any further work, the heap initialization code is
called once the module is linked in.
While it would be possible to add explicit calls to initialization functions in the startup code, the new approach has several advantages:
The symbols are sorted in increasing priority order by the linker when using one of the builtin linker configurations, so the functions with lower priorities come first and are followed by those with higher priorities. The C library runtime subroutine that walks over the function tables calls the functions starting from the top of the table - which means that functions with a high priority are called first.
So when using the C runtime, functions are called with high priority functions first, followed by low priority functions.
When using these special symbols, please take care of the following:
condes
and callirq
modules
in the C runtime for an example on how to do this.
FEATURE CONDES
statement in the linker config file. Each table has to
be requested separately.
.CONSTRUCTOR
,
.DESTRUCTOR
and
.INTERRUPTOR
statements, there is also a more generic command:
.CONDES
. This allows to specify an
additional type. Predefined types are 0 (constructor), 1 (destructor) and 2
(interruptor). The linker generates a separate table for each type on request.
Sometimes it is necessary to port code written for older assemblers to ca65.
In some cases, this can be done without any changes to the source code by
using the emulation features of ca65 (see
.FEATURE
). In other cases, it is necessary to make changes to the
source code.
Probably the biggest difference is the handling of the
.ORG
directive. ca65 generates relocatable code, and placement is
done by the linker. Most other assemblers generate absolute code, placement is
done within the assembler and there is no external linker.
In general it is not a good idea to write new code using the emulation features of the assembler, but there may be situations where even this rule is not valid.
You need to use some of the ca65 emulation features to simulate the behaviour of such simple assemblers.
; if you want TASS style labels without colons
.feature labels_without_colons
; if you want TASS style character constants
; ("a" instead of the default 'a')
.feature loose_char_term
.word *+2 ; the cbm load address
[yourcode here]
notice that the two emulation features are mostly useful for porting
sources originally written in/for TASS, they are not needed for the
actual "simple assembler operation" and are not recommended if you are
writing new code from scratch.
.RES
directive.
; *=$2000
.res $2000-* ; reserve memory up to $2000
Please note that other than the original TASS, ca65 can never move the program
counter backwards - think of it as if you are assembling to disk with TASS.
.ifeq
/.endif
/.goto
etc.) must be
rewritten to match ca65 syntax. Most importantly notice that due to the lack
of .goto
, everything involving loops must be replaced by
.REPEAT
.
.ORG
directive instead of
.offs
-constructs.
.org $1800
[floppy code here]
.reloc ; back to normal
cl65 --start-addr 0x0ffe -t none myprog.s -o myprog.prg
Note that you need to use the actual start address minus two, since two bytes
are used for the cbm load address.
ca65 (and all cc65 binutils) are (C) Copyright 1998-2003 Ullrich von Bassewitz. For usage of the binaries and/or sources the following conditions do apply:
This software is provided 'as-is', without any expressed or implied warranty. In no event will the authors be held liable for any damages arising from the use of this software.
Permission is granted to anyone to use this software for any purpose, including commercial applications, and to alter it and redistribute it freely, subject to the following restrictions: