# Skool files

A skool file contains the list of Z80 instructions that make up the routines and data blocks of the program being disassembled, with accompanying comments (if any).

## Skool file format

A skool file must be in a certain format to ensure that it is processed correctly by skool2html.py, skool2asm.py and skool2ctl.py. The rules are as follows:

- entries (an ‘entry’ being a routine or data block) must be separated by blank lines, and an entry must not contain any blank lines

- an entry header is a sequence of comment lines broken into four sections; see Entry header format

- each line in an entry may start with one of the following characters: `;* @bcgistuw`; see Entry line format

- tables (grids) have their own markup syntax; see #TABLE for details

### Entry header format

An entry header is a sequence of comment lines broken into four sections:

- entry title

- entry description (optional)

- registers (optional)

- start comment (optional)

The sections are separated by an empty comment line, and paragraphs within the entry description and start comment must be separated by a comment line containing a dot (`.`) on its own. For example:

    ; This is the entry title
    ;
    ; This is the first paragraph of the entry description.
    ; .
    ; This is the second paragraph of the entry description.
    ;
    ; A An important parameter
    ; B Another important parameter
    ;
    ; This is the start comment above the first instruction in the entry.

If a start comment is required but a register section is not, either append the start comment to the entry description, or specify a blank register section by using a dot (`.`) thus:

    ; This entry has a start comment but no register section
    ;
    ; This is the entry description.
    ;
    ; .
    ;
    ; This is the start comment above the first instruction in the entry.

Likewise, if a register section is required but an entry description is not, a blank entry description may be specified by using a dot (`.`) thus:

    ; This entry has a register section but no description
    ;
    ; .
    ;
    ; A An important parameter
    ; B Another important parameter

Register names may be given as shown above, or with colon-terminated prefixes (such as ‘Input:’ and ‘Output:’, or simply ‘I:’ and ‘O:’) to distinguish input values from output values:

    ;  Input:A An important parameter
    ;        B Another important parameter
    ; Output:C The result

In the HTML version of the disassembly, input values and output values are shown in separate tables. If a register’s prefix begins with the letter ‘O’, it is regarded as an output value; if it begins with any other letter, it is regarded as an input value. If a register has no prefix, it will be placed in the same table as the previous register; if there is no previous register, it will be placed in the table of input values.

If a register description is very long, it may be split over two or more lines by starting the second and subsequent lines with a dot (`.`) thus:

    ; HL The description for this register is quite long, so it is split over two
    ; .  lines for improved readability

Note that by default, the register name is separated from the description by whitespace and must not contain skool macros. If whitespace or skool macros are required in the register name field, then it must be delimited in the same way as an arbitrary string parameter of a skool macro. For example:

    ; (Output:B, D) The answers are in these two registers
    ; /(#R32768)/ The result is placed at this address

When a register name is supplied in this format, the delimiter characters must be something other than a letter or digit. In addition, #LIST and #TABLE macros in a register name field are not expanded in ASM mode.

### Entry line format

Each line in an entry may start with one of `;* @bcgistuw`, where:

- `;` begins a comment line

- `*` denotes an entry point in a routine

- `@` begins an ASM directive

- `b` denotes the first instruction in a data block

- `c` denotes the first instruction in a code block (routine)

- `g` denotes the first instruction in a game status buffer entry

- `i` denotes an ignored entry

- `s` denotes the first instruction in a data block containing bytes that are all the same value (typically unused zeroes)

- `t` denotes the first instruction in a data block that contains text

- `u` denotes the first instruction in an unused code or data block

- `w` denotes the first instruction in a data block that contains two-byte values (words)

- a space begins a line that does not require any of the markers listed above

The format of a line containing an instruction is:

    C##### INSTRUCTION[ ; comment]

where:

- `C` is one of the characters listed above: `* bcdgirstuw`

- `#####` is an address (e.g. `24576`, or `$6000` if you prefer hexadecimal notation)

- `INSTRUCTION` is an instruction (e.g. `LD A,(HL)`)

- `comment` is a comment (which may be blank)

The comment for a single instruction may span multiple lines thus:

    c24296 CALL 57935    ; This comment is too long to fit on a single line, so
                         ; we use two lines

A comment may also be associated with more than one instruction by the use of braces (`{` and `}`) to indicate the start and end points, thus:

    *24372 SUB D         ; {This comment applies to the two instructions at
     24373 JR NZ,24378   ; 24372 and 24373}

The opening and closing braces are removed before the comment is rendered in ASM or HTML mode. (See Braces in comments.)

Comments may appear between instructions, or after the last instruction in an entry; paragraphs in such comments must be separated by a comment line containing a dot (`.`) on its own. For example:

    *28975 JR 28902
    ; This is a mid-block comment between two instructions.
    ; .
    ; This is the second paragraph of the comment.
     28977 XOR A

Lines that start with `*` will have their addresses shown in bold in the HTML version of the disassembly (generated by skool2html.py), and will have labels generated for them in the ASM version (generated by skool2asm.py).

## ASM directives

To write an ASM directive in a skool file, start a line with `@`; for example:

    ; Start the game
    @label=START
    c24576 XOR A

See ASM modes and directives for more details.

## Escaping characters

Backslash (`\`) and double quote (`"`) characters in string and character operands must be escaped by preceding them with a backslash. For example:

    c32768 LD A,"\""     ; LD A,34
     32770 LD B,"\\"     ; LD B,92

This ensures that SkoolKit or an assembler can parse such operands correctly.

## Braces in comments

As noted above, opening and closing braces (`{`, `}`) are used to mark the start and end points of an instruction-level comment that is associated with more than one instruction, and the braces are removed before the comment is rendered. This means that if the comment requires an opening or closing brace when rendered, some care must be taken to get the syntax correct.

The rules regarding an instruction-level comment that starts with an opening brace are as follows:

- The comment terminates on the line where the total number of closing braces in the comment becomes equal to or greater than the total number of opening braces

- Adjacent opening braces at the start of the comment are removed before rendering

- Adjacent closing braces at the end of the comment are removed before rendering

By these rules, it is possible to craft an instruction-level comment that contains matched or unmatched opening and closing braces when rendered.

For example:

    b50000 DEFB 0  ; {{This comment (which spans two instructions) has an
     50001 DEFB 0  ; unmatched closing brace} }

will render in ASM mode as:

    DEFB 0                  ; This comment (which spans two instructions) has an
    DEFB 0                  ; unmatched closing brace}

And:

    b50002 DEFB 0  ; { {{Matched opening and closing braces}} }

will render as:

    DEFB 0                  ; {{Matched opening and closing braces}}

Finally:

    b50003 DEFB 0  ; { {Unmatched opening brace}}

will render as:

    DEFB 0                  ; {Unmatched opening brace

## Non-entry blocks

In addition to regular entries (routines and data blocks), a skool file may also contain blocks of lines that do not match the format of an entry, such as a header comment that appears before the first entry and contains copyright information. For example:

    ; Copyright 2018 J Smith

    ; Start
    c24576 JP 32768

Non-entry blocks such as this copyright comment are reproduced by skool2asm.py, ignored by skool2html.py, and preserved verbatim by skool2ctl.py.

To qualify as a regular entry, a block must contain at least one line that starts with `b`, `c`, `g`, `i`, `s`, `t`, `u` or `w` when parsed in the relevant substitution mode or bugfix mode (which depends on the command being run).

So, for example:

    @isub-begin
    c24573 JP 32768
    @isub-end

is seen as a regular entry (without the `@isub` block directives) by skool2ctl.py and skool2html.py, but is invisible to skool2asm.py. And:

    @isub+begin
    c24573 JP 32768
    @isub+end

is seen as a non-entry block (with the `@isub` block directives retained) by skool2ctl.py and skool2html.py, but as a regular entry (without the `@isub` block directives) by skool2asm.py.

## Revision history

Version | Changes
--- | ---
8.1 | Register name fields may contain whitespace and skool macros
4.3 | Added support for the start comment in entry headers; an ASM directive can be declared by starting a line with `@`
4.2 | Added support for splitting register descriptions over multiple lines
3.7 | Added support for binary numbers; added the `s` block type
3.1.2 | Added support for ‘Input’ and ‘Output’ prefixes in register sections
2.4 | Added the ability to separate paragraphs and specify a blank entry description by using a dot (`.`) on a line of its own
2.1 | Added support for hexadecimal numbers