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3.6. Assembler Directives

Various directives can be used to control the behaviour of the assembler or to include non-code/data in the resulting output. Those directives that are not described in detail in other sections of this document are described below.

3.6.1. Data Directives

FCB expr[,...], .DB expr[,...], .BYTE expr[,...]: Include one or more constant bytes (separated by commas) in the output.
FDB expr[,...], .DW expr[,...], .WORD expr[,...]: Include one or more words (separated by commas) in the output.
FQB expr[,...], .QUAD expr[,...], .4BYTE expr[,...]: Include one or more double words (separated by commas) in the output.
FCC string, .ASCII string, .STR string: Include a string of text in the output. The first character of the operand is the delimiter which must appear as the last character and cannot appear within the string. The string is included with no modifications>
FCN string, .ASCIZ string, .STRZ string: Include a NUL terminated string of text in the output. The first character of the operand is the delimiter which must appear as the last character and cannot appear within the string. A NUL byte is automatically appended to the string.
FCS string, .ASCIS string, .STRS string: Include a string of text in the output with bit 7 of the final byte set. The first character of the operand is the delimiter which must appear as the last character and cannot appear within the string.
ZMB expr: Include a number of NUL bytes in the output. The number must be fully resolvable during pass 1 of assembly so no forward or external references are permitted.
ZMD expr: Include a number of zero words in the output. The number must be fully resolvable during pass 1 of assembly so no forward or external references are permitted.
ZMQ expr: Include a number of zero double-words in the output. The number must be fully resolvable during pass 1 of assembly so no forward or external references are permitted.
RMB expr, .BLKB expr, .DS expr, .RS expr: Reserve a number of bytes in the output. The number must be fully resolvable during pass 1 of assembly so no forward or external references are permitted. The value of the bytes is undefined.
RMD expr: Reserve a number of words in the output. The number must be fully resolvable during pass 1 of assembly so no forward or external references are permitted. The value of the words is undefined.
RMQ expr: Reserve a number of double-words in the output. The number must be fully resolvable during pass 1 of assembly so no forward or external references are permitted. The value of the double-words is undefined.

3.6.2. Address Definition

The directives in this section all control the addresses of symbols or the assembly process itself.

ORG expr

Set the assembly address. The address must be fully resolvable on the first pass so no external or forward references are permitted. ORG is not permitted within sections when outputting to object files. For the DECB target, each ORG directive after which output is generated will cause a new preamble to be output. ORG is only used to determine the addresses of symbols when the raw target is used.

sym EQU expr, sym = expr

Define the value of sym to be expr.

sym SET expr

Define the value of sym to be expr. Unlike EQU, SET permits symbols to be defined multiple times as long as SET is used for all instances. Use of the symbol before the first SET statement that sets its value is undefined.

SETDP expr

Inform the assembler that it can assume the DP register contains expr. This directive is only advice to the assembler to determine whether an address is in the direct page and has no effect on the contents of the DP register. The value must be fully resolved during the first assembly pass because it affects the sizes of subsequent instructions.

This directive has no effect in the object file target.

ALIGN expr

Force the current assembly address to be a multiple of expr. A series of NUL bytes is output to force the alignment, if required. The alignment value must be fully resolved on the first pass because it affects the addresses of subsquent instructions.

This directive is not suitable for inclusion in the middle of actual code. It is intended to appear where the bytes output will not be executed.

3.6.3. Conditional Assembly

Portions of the source code can be excluded or included based on conditions known at assembly time. Conditionals can be nested arbitrarily deeply. The directives associated with conditional assembly are described in this section.

All conditionals must be fully bracketed. That is, every conditional statement must eventually be followed by an ENDC at the same level of nesting.

Conditional expressions are only evaluated on the first assembly pass. It is not possible to game the assembly process by having a conditional change its value between assembly passes. Thus there is not and never will be any equivalent of IFP1 or IFP2 as provided by other assemblers.

IFEQ expr: If expr evaluates to zero, the conditional will be considered true.
IFNE expr, IF expr: If expr evaluates to a non-zero value, the conditional will be considered true.
IFGT expr: If expr evaluates to a value greater than zero, the conditional will be considered true.
IFGE expr: If expr evaluates to a value greater than or equal to zero, the conditional will be considered true.
IFLT expr: If expr evaluates to a value less than zero, the conditional will be considered true.
IFLE expr: If expr evaluates to a value less than or equal to zero , the conditional will be considered true.
IFDEF sym: If sym is defined at this point in the assembly process, the conditional will be considered true.
IFNDEF sym: If sym is not defined at this point in the assembly process, the conditional will be considered true.
ELSE: If the preceding conditional at the same level of nesting was false, the statements following will be assembled. If the preceding conditional at the same level was true, the statements following will not be assembled. Note that the preceding conditional might have been another ELSE statement although this behaviour is not guaranteed to be supported in future versions of LWASM.
ENDC: This directive marks the end of a conditional construct. Every conditional construct must end with an ENDC directive.

3.6.4. Miscelaneous Directives

This section includes directives that do not fit into the other categories.

INCLUDE filename

Include the contents of filename at this point in the assembly as though it were a part of the file currently being processed. Note that whitespace cannot appear in the name of the file.

END [expr]

This directive causes the assembler to stop assembling immediately as though it ran out of input. For the DECB target only, expr can be used to set the execution address of the resulting binary. For all other targets, specifying expr will cause an error.

ERROR string

Causes a custom error message to be printed at this line. This will cause assembly to fail. This directive is most useful inside conditional constructs to cause assembly to fail if some condition that is known bad happens.

.MODULE string

This directive is ignored for most output targets. If the output target supports encoding a module name into it, string will be used as the module name.

As of version 2.2, no supported output targets support this directive.

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