A skool file may contain directives that are processed when parsing in ASM mode. 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.
There are three substitution modes: @isub, @ssub, and @rsub. These modes are described in the following subsections.
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.
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.
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.
There are three bugfix modes: @ofix, @bfix and @rfix. These modes are described in the following subsections.
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 -f1 option to skool2asm.py.
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 -f2 option to skool2asm.py.
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 -f3 option to skool2asm.py. @rfix mode implies @rsub mode (see @rsub mode).
The ASM directives recognised by SkoolKit are described in the following subsections.
The @bfix directive is used to make an instruction substitution in @bfix mode.
; @bfix=INSTRUCTION
For example:
; @bfix=DEFM "Phosphorus"
t57532 DEFM "Phosphorous"
The @bfix block directives are used to 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
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.
The @ignoredua directive is used to suppress any warnings that would otherwise be reported concerning addresses not converted to labels in the description of an entry.
; @ignoredua
For example:
; Prepare data
;
; @ignoredua
; This routine operates on the data at 32768.
If the @ignoredua directive were not present, a warning would be printed (during the rendering phase) about the comment containing an address (32768) that has not been converted to a label.
The @ignoremrcua directive is used to suppress any warnings that would otherwise be reported concerning addresses not converted to labels in the mid-routine comment above the next instruction.
; @ignoremrcua
For example:
28913 LD L,A
; @ignoremrcua
; #REGhl now holds either 32522 or 32600.
28914 LD B,(HL)
If the @ignoremrcua 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.
The @ignoreua directive is used to suppress any warnings that would otherwise be reported concerning addresses not converted to labels in the comment for the next instruction.
; @ignoreua
For example:
; @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.
The @isub directive is used to make an instruction substitution in @isub mode.
; @isub=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.
The @isub block directives are used to 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.
The @keep directive is used to prevent 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 (assuming there is a routine at that address); however, the operand is meant to be a pure data value, not a variable or routine address.
The @label directive sets the label for the next instruction.
; @label=LABEL
For example:
; @label=ENDGAME
c24576 XOR A
This sets the label for the routine at 24576 to ENDGAME.
The @nolabel directive is used to prevent 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
The @nowarn directive is used to suppress any warnings that would otherwise be reported for the next instruction concerning:
; @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).
The @ofix directive is used to make an instruction substitution in @ofix mode.
; @ofix=INSTRUCTION
For example:
; @ofix=JR NZ,26067
25989 JR NZ,26068
This @ofix directive replaces the operand of the JR NZ instruction with 26067.
The @ofix block directives are used to 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.
The @org directive inserts an ORG assembler directive.
; @org=ADDRESS
The @rem directive is 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
For example:
; @rem=The next section of data MUST start at 64000
; @org=64000
The @rfix block directives are used to 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.
The @rsub directive is used to make an instruction substitution in @rsub mode.
; @rsub=INSTRUCTION
For example:
; @rsub=INC BC
30143 INC C ; Point #REGbc at the next byte of data
The @rsub block directives are used to 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.
The @ssub directive is used to make an instruction substitution in @ssub mode.
; @ssub=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.)