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; see below for a description of @ofix mode and the other bugfix modes.
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
; @rsub+begin
LD A,H
OR L
; @rsub+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 (see @rsub mode).
ASM directives¶
The ASM directives recognised by SkoolKit are described in the following subsections.
@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 should 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.
; @end
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 mid-block comment, a block end comment, or an instruction-level comment.
; @ignoreua
To apply the directive to an entry title:
; @ignoreua
; Prepare data at 32768
;
; This routine operates on the data in page 128.
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.
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 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 |
|---|---|
| 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).
; @keep
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.
; @nolabel
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)
; @nowarn
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 the ORG 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 |
@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=INC BC
30143 INC C ; Point #REGbc at the next byte of data
@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 name
- value is the property value
@set directives should 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, or 0 to use the system default (default: 0)
- handle-unsupported-macros - how to handle an unsupported macro: 1 to expand it to an empty string, or 0 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, or 0 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, or 0 to use spaces (default: 0)
- warnings - 1 to print any warnings that are produced while writing ASM output (after parsing the skool file), or 0 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 |
|---|---|
| 3.2 | New |
| 3.3.1 | Added the comment-width-min, indent, instruction-width, label-colons, line-width and warnings properties |
| 3.4 | Added the handle-unsupported-macros and wrap-column-width-min properties |
@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.)
@start¶
The @start directive must be used to indicate where to start parsing the skool file for the purpose of generating ASM output. Everything before the @start directive is ignored.
; @start
See also @end.
@writer¶
The @writer directive specifies the name of the Python class to use to generate ASM output. It should 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 |
|---|---|
| 3.1 | New |
| 3.3.1 | Added support for specifying a module outside the module search path |