ASM modes and directives¶
A skool file may contain directives that are processed during the parsing phase. Exactly how a directive is processed (and whether it is executed) depends on the ‘substitution mode’ and ‘bugfix mode’ in which the skool file is being parsed.
Substitution modes¶
There are three substitution modes: @isub
, @ssub
, and @rsub
. These
modes are described in the following subsections.
@isub mode¶
In @isub
mode, @isub
directives are executed, but @ssub
, and
@rsub
directives are not. The main purpose of @isub
mode is to make the
minimum number of instruction substitutions necessary to produce an ASM file
that assembles.
For example:
@isub=LD A,(32512)
25396 LD A,(m)
This @isub
directive ensures that LD A,(m)
is replaced by the valid
instruction LD A,(32512)
when rendering in ASM mode.
@isub
mode is invoked by default when running
skool2asm.py.
@ssub mode¶
In @ssub
mode, @isub
and @ssub
directives are executed, but
@rsub
directives are not. The main purpose of @ssub
mode is to replace
LSBs, MSBs and full addresses in the operands of instructions with labels, to
make the code amenable to some degree of relocation, but without actually
removing or inserting any code.
For example:
@ssub=LD (27015+1),A
*27012 LD (27016),A ; Change the instruction below from SET 0,B to RES 0,B
; or vice versa
27015 SET 0,B
This @ssub
directive replaces LD (27016),A
with LD (27015+1),A
; the
27015
will be replaced by the label for that address before rendering.
(27016
cannot be replaced by a label, since it is not the address of an
instruction.)
@ssub
mode is invoked by passing the -s
option to
skool2asm.py.
@rsub mode¶
In @rsub
mode, @isub
, @ssub
and @rsub
directives are executed.
The main purpose of @rsub
mode is to make code unconditionally relocatable,
even if that requires the removal of existing code or the insertion of new
code.
For example:
23997 LD HL,32766
@ssub=LD (HL),24002%256
24000 LD (HL),194
@rsub+begin
INC L
LD (HL),24002/256
@rsub+end
24002 XOR A
This @rsub
block directive inserts two instructions that ensure that the
address stored at 32766 will have the correct MSB as well as the correct LSB,
regardless of where the code originally at 24002 now lives.
@rsub
mode is invoked by passing the -r
option to
skool2asm.py. @rsub
mode also implies
@ofix mode.
Bugfix modes¶
There are three bugfix modes: @ofix
, @bfix
and @rfix
. These
modes are described in the following subsections.
@ofix mode¶
In @ofix
mode, @ofix
directives are executed, but @bfix
and
@rfix
directives are not. The main purpose of @ofix
mode is to fix
instructions that have faulty operands.
For example:
@ofix-begin
27872 CALL 27633 ; This should be CALL 27634
@ofix+else
CALL 27634
@ofix+end
These @ofix
block directives fix the faulty operand of the CALL
instruction.
@ofix
mode is invoked by passing the -f 1
option to
skool2asm.py.
@bfix mode¶
In @bfix
mode, @ofix
and @bfix
directives are executed, but
@rfix
directives are not. The main purpose of @bfix
mode is to fix bugs
by replacing instructions, but without changing the start address of any
routines, routine entry points, or data blocks.
For example:
@bfix-begin
32205 JR Z,32232 ; This should be JR NZ,32232
@bfix+else
JR NZ,32232 ;
@bfix+end
@bfix
mode is invoked by passing the -f 2
option to
skool2asm.py.
@rfix mode¶
In @rfix
mode, @ofix
, @bfix
and @rfix
directives are executed.
The purpose of @rfix
mode is to fix bugs that cannot be fixed without
moving code around (to make space for the fix).
For example:
28432 DEC HL
@rfix+begin
LD A,H
OR L
@rfix+end
28433 JP Z,29712
These @rfix
block directives insert some instructions to fix the faulty
check on whether HL holds 0.
@rfix
mode is invoked by passing the -f 3
option to
skool2asm.py. @rfix
mode implies @rsub mode.
ASM directives¶
The ASM directives recognised by SkoolKit are described in the following subsections.
@assemble¶
The @assemble
directive controls whether assembly language instructions
are converted into byte values for the purpose of populating the memory
snapshot.
@assemble=N
N
is1
to start converting at the next instruction, or0
to stop
For example:
; The eight bytes of code in this routine are also used as UDG data.
; .
; #HTML(#UDG44919)
@assemble=1
c44919 LD DE,46572 ;
44922 CP 200 ;
44924 JP 45429 ;
@assemble=0
The @assemble=1
directive is required to define the bytes for addresses
44919-44926. If it were not present, the memory snapshot would contain zeroes
at those addresses, and the image created by the #UDG
macro would be blank.
Note that DEFB
, DEFM
, DEFS
and DEFW
statements are always
converted into byte values and inserted into the memory snapshot; the
@assemble
directive is only required for assembly language instructions.
Version | Changes |
---|---|
5.0 | New |
@bfix¶
The @bfix
directive makes an instruction substitution in @bfix mode.
@bfix=INSTRUCTION
INSTRUCTION
is the replacement instruction
For example:
@bfix=DEFM "Phosphorus"
t57532 DEFM "Phosphorous"
@bfix block directives¶
The @bfix
block directives define a block of lines that will be inserted or
removed in @bfix mode.
The syntax for defining a block that will be inserted in @bfix
mode (but
left out otherwise) is:
@bfix+begin
... ; Lines to be inserted
@bfix+end
The syntax for defining a block that will be removed in @bfix
mode (but
left in otherwise) is:
@bfix-begin
... ; Lines to be removed
@bfix-end
Typically, though, it is desirable to define a block that will be removed in
@bfix
mode right next to the block that will be inserted in its place. That
may be done thus:
@bfix-begin
... ; Instructions to be removed
@bfix+else
... ; Instructions to be inserted
@bfix+end
which is equivalent to:
@bfix-begin
... ; Instructions to be removed
@bfix-end
@bfix+begin
... ; Instructions to be inserted
@bfix+end
For example:
@bfix-begin
32205 JR Z,32232 ; This should be JR NZ,32232
@bfix+else
JR NZ,32232 ;
@bfix+end
@end¶
The @end
directive may be used to indicate where to stop parsing the skool
file for the purpose of generating ASM output. Everything after the @end
directive is ignored by skool2asm.py.
See also @start.
Version | Changes |
---|---|
2.2.2 | New |
@ignoreua¶
The @ignoreua
directive suppresses any warnings that would otherwise be
reported concerning addresses not converted to labels in the comment that
follows; the comment may be an entry title, an entry description, a register
description section, a block start comment, a mid-block comment, a block end
comment, or an instruction-level comment.
To apply the directive to an entry title:
@ignoreua
; Prepare data at 32768
c32768 LD A,(HL)
If the @ignoreua
directive were not present, a warning would be printed
(during the rendering phase) about the entry title containing an address
(32768) that has not been converted to a label.
To apply the directive to an entry description:
; Prepare data in page 128
;
@ignoreua
; This routine operates on the data at 32768.
c49152 LD A,(HL)
If the @ignoreua
directive were not present, a warning would be printed
(during the rendering phase) about the entry description containing an address
(32768) that has not been converted to a label.
To apply the directive to a register description section:
; Prepare data in page 128
;
; This routine operates on the data in page 128.
;
@ignoreua
; HL 32768
c49152 LD A,(HL)
If the @ignoreua
directive were not present, a warning would be printed
(during the rendering phase) about the register description containing an
address (32768) that has not been converted to a label.
To apply the directive to a block start comment:
; Prepare data in page 128
;
; This routine operates on the data in page 128.
;
; HL 128*256
;
@ignoreua
; First pick up the byte at 32768.
c49152 LD A,(HL)
If the @ignoreua
directive were not present, a warning would be printed
(during the rendering phase) about the start comment containing an address
(32768) that has not been converted to a label.
To apply the directive to a mid-block comment:
28913 LD L,A
@ignoreua
; #REGhl now holds either 32522 or 32600.
28914 LD B,(HL)
If the @ignoreua
directive were not present, warnings would be printed
(during the rendering phase) about the comment containing addresses (32522,
32600) that have not been converted to labels.
To apply the directive to a block end comment:
44159 JP 63152
@ignoreua
; This routine continues at 63152.
If the @ignoreua
directive were not present, warnings would be printed
(during the rendering phase) about the comment containing an address (63152)
that has not been converted to a label.
To apply the directive to an instruction-level comment:
@ignoreua
60159 LD C,A ; #REGbc now holds 62818
If the @ignoreua
directive were not present, a warning would be printed
(during the rendering phase) about the comment containing an address (62818)
that has not been converted to a label.
Version | Changes |
---|---|
4.2 | Added support for register description sections |
2.4.1 | Added support for entry titles, entry descriptions, mid-block comments and block end comments |
@isub¶
The @isub
directive makes an instruction substitution in @isub mode.
@isub=INSTRUCTION
INSTRUCTION
is the replacement instruction
For example:
@isub=LD A,(32512)
25396 LD A,(m)
This @isub
directive ensures that LD A,(m)
is replaced by the valid
instruction LD A,(32512)
when rendering in ASM mode.
@isub block directives¶
The @isub
block directives define a block of lines that will be inserted or
removed in @isub mode.
The syntax is equivalent to that for the @bfix block directives.
@keep¶
The @keep
directive prevents the substitution of a label for the operand in
the next instruction (but only when the instruction has not been replaced using
an @isub
or @ssub
directive).
For example:
@keep
28328 LD BC,24576 ; #REGb=96, #REGc=0
If the @keep
directive were not present, the operand (24576) of the
LD BC
instruction would be replaced with the label of the routine at 24576
(if there is a routine at that address); however, the operand is meant to be a
pure data value, not a variable or routine address.
@label¶
The @label
directive sets the label for the next instruction.
@label=LABEL
LABEL
is the label to apply
For example:
@label=ENDGAME
c24576 XOR A
This sets the label for the routine at 24576 to ENDGAME
.
@nolabel¶
The @nolabel
directive prevents the next instruction from having a label
automatically generated.
For example:
@label=TOGGLE
c48998 LD HL,32769
@bfix+begin
@label=LOOP
@bfix+end
49001 LD A,(HL)
@bfix+begin
@nolabel
@bfix+end
*49002 XOR L
49003 LD (HL),A
49004 INC L
@bfix-begin
49005 JR NZ,49002
@bfix+else
49005 JR NZ,49001
@bfix+end
The @nolabel
directive here prevents the instruction at 49002 from being
labelled in @bfix mode (because no label is required; instead, the
previous instruction at 49001 will be labelled).
The output in @bfix
mode will be:
TOGGLE:
LD HL,32769
LOOP:
LD A,(HL)
XOR L
LD (HL),A
INC L
JR NZ,LOOP
And the output when not in @bfix
mode will be:
TOGGLE:
LD HL,32769
LD A,(HL)
TOGGLE_0:
XOR L
LD (HL),A
INC L
JR NZ,TOGGLE_0
@nowarn¶
The @nowarn
directive suppresses any warnings that would otherwise be
reported for the next instruction concerning:
- a
LD
operand being replaced with a routine label (if the instruction has not been replaced using@isub
or@ssub
) - an operand not being replaced with a label (because the operand address has no label)
For example:
@nowarn
25560 LD BC,25404 ; Point #REGbc at the routine at #R25404
If this @nowarn
directive were not present, a warning would be printed
(during the parsing phase) about the operand (25404) being replaced with a
routine label (which would be inappropriate if 25404 were intended to be a pure
data value).
For another example:
@ofix-begin
@nowarn
27872 CALL 27633 ; This should be CALL #R27634
@ofix+else
CALL 27634 ;
@ofix+end
If this @nowarn
directive were not present, a warning would be printed
(during the parsing phase, if not in @ofix mode) about the operand (27633)
not being replaced with a label (usually you would want the operand of a CALL
instruction to be replaced with a label, but not in this case).
@ofix¶
The @ofix
directive makes an instruction substitution in @ofix mode.
@ofix=INSTRUCTION
INSTRUCTION
is the replacement instruction (with a corrected operand)
For example:
@ofix=JR NZ,26067
25989 JR NZ,26068
This @ofix
directive replaces the operand of the JR NZ
instruction with
26067.
@ofix block directives¶
The @ofix
block directives define a block of lines that will be inserted or
removed in @ofix mode.
The syntax is equivalent to that for the @bfix block directives.
@org¶
The @org
directive inserts an ORG
assembler directive.
@org=ADDRESS
ADDRESS
is theORG
address
@rem¶
The @rem
directive may be used to make an illuminating comment about a
nearby section or other ASM directive in a skool file. The directive is ignored
by the parser.
@rem=COMMENT
COMMENT
is a suitably illuminating comment
For example:
@rem=The next section of data MUST start at 64000
@org=64000
Version | Changes |
---|---|
2.4 | The = is required |
@replace¶
The @replace
directive replaces strings that match a regular expression in
skool file annotations and ref file sections.
@replace=/pattern/repl
pattern
is the regular expressionrepl
is the replacement string
For example:
@replace=/#copy/#CHR(169)
This @replace
directive replaces all instances of #copy
with
#CHR(169)
.
If /
appears anywhere in pattern
or repl
, then an alternative
separator should be used; for example:
@replace=|n/a|not applicable
As a convenience for dealing with decimal and hexadecimal numbers, wherever
\i
appears in pattern
, it is replaced by a regular expression group
that matches a decimal number or a hexadecimal number preceded by $
. For
example:
@replace=/#udg\i,\i/#UDG(\1,#PEEK\2)
This @replace
directive would replace #udg$a001,40960
with
#UDG($a001,#PEEK40960)
.
Note that string replacements specified by @replace
directives are made
before skool macros are expanded, and in the order in which the directives
appear in the skool file. For example, if we have:
@replace=/#foo\i/#bar\1
@replace=/#bar\i/#EVAL\1,16
then #foo31
would be replaced by #EVAL31,16
, but if these directives
were reversed:
@replace=/#bar\i/#EVAL\1,16
@replace=/#foo\i/#bar\1
then #foo31
would be replaced by #bar31
.
See also Defining macros with @replace.
Version | Changes |
---|---|
5.1 | New |
@rfix¶
The @rfix
directive makes an instruction substitution in @rfix mode.
@rfix=INSTRUCTION
INSTRUCTION
is the replacement instruction
For example:
@rfix=LD HL,0
27519 LD L,0
Version | Changes |
---|---|
5.2 | New |
@rfix block directives¶
The @rfix
block directives define a block of lines that will be inserted or
removed in @rfix mode.
The syntax is equivalent to that for the @bfix block directives.
@rsub¶
The @rsub
directive makes an instruction substitution in @rsub mode.
@rsub=INSTRUCTION
INSTRUCTION
is the replacement instruction
For example:
@rsub=LD BC,0
30143 LD C,0 ; Reset #REGbc to 0
@rsub block directives¶
The @rsub
block directives define a block of lines that will be inserted or
removed in @rsub mode.
The syntax is equivalent to that for the @bfix block directives.
@set¶
The @set
directive sets a property on the ASM writer.
@set-name=value
name
is the property namevalue
is the property value
@set
directives must be placed somewhere after the @start directive,
and before the @end directive (if there is one).
Recognised property names and their default values are:
bullet
- the bullet character(s) to use for list items specified in a #LIST macro (default:*
)comment-width-min
- the minimum width of the instruction comment field (default:10
)crlf
-1
to use CR+LF to terminate lines, or0
to use the system default (default:0
)handle-unsupported-macros
- how to handle an unsupported macro:1
to expand it to an empty string, or0
to exit with an error (default:0
)indent
- the number of spaces by which to indent instructions (default:2
)instruction-width
- the width of the instruction field (default:23
)label-colons
-1
to append a colon to labels, or0
to leave labels unadorned (default:1
)line-width
- the maximum width of each line (default:79
)tab
-1
to use a tab character to indent instructions, or0
to use spaces (default:0
)warnings
-1
to print any warnings that are produced while writing ASM output (after parsing the skool file), or0
to suppress them (default:1
)wrap-column-width-min
- the minimum width of a wrappable table column (default:10
)
For example:
@set-bullet=+
This @set
directive sets the bullet character to ‘+’.
Version | Changes |
---|---|
3.4 | Added the handle-unsupported-macros and wrap-column-width-min properties |
3.3.1 | Added the comment-width-min, indent, instruction-width, label-colons, line-width and warnings properties |
3.2 | New |
@ssub¶
The @ssub
directive makes an instruction substitution in @ssub mode.
@ssub=INSTRUCTION
INSTRUCTION
is the replacement instruction
For example:
@ssub=LD (27015+1),A
*27012 LD (27016),A ; Change the instruction below from SET 0,B to RES 0,B
; or vice versa
27015 SET 0,B
This @ssub
directive replaces LD (27016),A
with LD (27015+1),A
; the
27015
will be replaced by the label for that address before rendering.
(27016
cannot be replaced by a label, since it is not the address of an
instruction.)
@ssub block directives¶
The @ssub
block directives define a block of lines that will be inserted or
removed in @ssub mode.
The syntax is equivalent to that for the @bfix block directives.
Version | Changes |
---|---|
4.4 | New |
@start¶
The @start
directive indicates where to start parsing the skool file for
the purpose of generating ASM output. Everything before the @start
directive is ignored by skool2asm.py.
See also @end.
@writer¶
The @writer
directive specifies the name of the Python class to use to
generate ASM output. It must be placed somewhere after the @start
directive, and before the @end directive (if there is one).
@writer=package.module.classname
or:
@writer=/path/to/moduledir:module.classname
The second of these forms may be used to specify a class in a module that is outside the module search path (e.g. a standalone module that is not part of an installed package).
The default ASM writer class is skoolkit.skoolasm.AsmWriter. For information on how to create your own Python class for generating ASM output, see the documentation on extending SkoolKit.
Version | Changes |
---|---|
3.3.1 | Added support for specifying a module outside the module search path |
3.1 | New |