
 -*[ NES ASM v2.51 ]*-
    ---------------


    Usage
    -----

        NESASM [-options] [-? (for help)] infile[.ASM]

        The assembler accepts only one input file 'infile' that will be
        assembled  into ROM file (.NES extension) directly useable
        by an emulator.

        A listing file can also be generated (.LST extension) if the LIST
        directive is encountered in the input file.

        Here's a description of the different options:


        Option  Description
        ------  -----------

         -s
         -S     Show segment usage. If one of those options is specified
                the assembler will display information on the ROM bank
                usage. Use '-s' to show basic information and '-S' to
                show more detailed information.

         -l #   Control output of the listing file:

                    0 - disable completely the listing file even if the
                        LIST directive is used in the input file
                    1 - minimun level; code produced by DB, DW and DEFCHR
                        will not be dumped
                    2 - normal level; only code produced by DEFCHR will not
                        be dumped
                    3 - maximun level; all the code is dumped in the
                        listing file

                The default level is level 2.

         -m     Force macros expansion in the listing file, even if the
                MLIST directive is not seen in the input file.

         -raw   Control the header generation. By default the assembler
                always adds an header to the ROM file; unless '-raw' is
                specified, in this case no ROM header is generated.


    Include path
    ------------

        By default the assembler looks in the current directory when
        loading an include file, but when it doesn't find the file it
        then uses the environment variable 'NES_INCLUDE' to get a list
        of include paths. Ideally, you will want to set this variable in
        your 'AUTOEXEC.BAT' file, and have it point to the 'NES'
        directory of MagicKit.

        ex:   set NES_INCLUDE=c:\magickit\nes


    Symbols
    -------

        Two types of symbol are supported, global symbols and local
        symbols. Local symbols are preceded by a dot '.' and are valid
        only between two global symbols. A symbol can be followed by
        a colon ':' but this is not necessary.


    Expressions
    -----------

        The assembler supports very complex expressions. You can use
        as many level of parenthesis as you want and spaces between
        operators and numbers are possible.
        
        Numbers can be written in three bases : hexadecimal ($7F), 
        binary (%0101) and decimal (48). Character values are also 
        supported ('A').

        All the usual operators are present :

            +, -, *, /, %, ^, &, |, ~, <<, >>

        As well as the comparison operators :

            =, !=, !, <, >, <=, >=

        For the priority, the same rules as C apply.

        You can also use predefined or user-defined functions in
        an expression.


        Predefined functions
        --------------------

            HIGH()   - Returns the high byte of a value.

            LOW()    - Returns the low byte.

            BANK()   - Returns the bank index of a symbol. If no symbol,
                       or more than one, are given, the function will 
                       return an error.

            PAGE()   - Returns the page index of a label. See above for
                       errors.

            SIZEOF() - Returns the size of a data element.


        User-defined functions
        ----------------------

            User-defined functions are declared with the .FUNC directive,
            for example:

                SCR_ADDR .func (\1) + ((\2) << 5)

            Up to nine arguments, \1 to \9, can be used.
                                                    
            To call a function simply enclose arguments within parenthesis
            and separate them with a comma:

                stw #SCR_ADDR(10,4)+$2000,<$20

            User-defined functions can be very useful, one often needs to use
            the same calculation again and again in expressions. Defining a
            function will save you a lot of work, and reduce typo errors. :)

            Note that function calls can be nested, you can call one function
            from another without any problem, however, recursive calls will
            produce an error.


    Macros
    ------

        While functions are very useful to replace common expressions by
        just a function call, macros are used to replace common groups
        of instructions by a single line of code. 

        You start a macro definition with:

            label  .macro

        Or you can also place the label after the '.macro' keyword, like
        this:

                   .macro label 

        After follow the body of the macro, which is terminated by
        the '.endm' directive.

        As an example let's define a 'neg' macro to negate the accumulator.

            neg    .macro
                    eor   #$FF
                    inc   A
                   .endm

        Macros can also have parameters. In the macro body, you refer to
        a parameter by using the backslash character ('\') followed by
        a digit. Nine parameters can be used, \1 to \9.

        Here's another example:

            add    .macro       ; add a value to register A
                    clc         ; (handle carry flag)
                    adc   \1+1
                   .endm

        Other 'special' parameters can be used, here's a list of all
        the possible parameter you can use inside a macro:


        Parameter  Description
        ---------  -----------
        \1  -  \9  Input parameter - up to nine can be used in a macro call

        \#         Number of input parameters

        \?1 - \?9  Returns 'type' of input parameter:
                     ARG_NONE      (= 0) = No argument
                     ARG_REG       (= 1) = register            -> A, X, Y
                     ARG_IMMEDIATE (= 2) = Immediate data type -> #xx
                     ARG_ABSOLUTE  (= 3) = Abosulte addressing -> label, $xxxx
                     ARG_INDIRECT  (= 4) = Indirect addressing -> [label]
                     ARG_STRING    (= 5) = String argument     -> "..."
                     ARG_LABEL     (= 6) = Label argument      -> label

        \@         Special parameter that returns a different number for
                   each macro; can be used to define local symbols inside
                   macros:

                       abs    .macro
                               lda   \1
                               bpl   .x\@
                               eor   #$FF
                               inc   A
                               sta   \1
                       .x\@:
                              .endm


    Directives
    ----------


        LIST    - Enable the listing file generation. You can later stop
                  temporarily the output with the NOLIST directive and
                  restart it again with LIST.

        NOLIST  - Stop the listing output.

        MLIST   - Allow macro expansion in the listing file.

        NOMLIST - Stop expanding macros in the listing file. This directive
                  won't have any effect if you use the '-m' command line
                  option.

        OPT     - ...

        EQU     - Assign a value to a symbol. The character '=' has
                  the same function too.

        BANK    - Select a 8KB ROM bank (0-127) and reset the location
                  counter to the latest known position in this bank.

        ORG     - Set the location of the program counter. The thirteen
                  lower bits of the address inform the assembler about
                  the offset in the ROM bank and the third upper bits
                  represent the page index.

        DB      - Store one or more data bytes at the current location.

        DW      - Store data words.

        BYTE    - Same as DB.

        WORD    - Same as DW.

        DS      - Reserve space at the current location. This space will
                  be filled with zeroes if this directive is used in the
                  CODE or DATA group.

        RSSET   - Set the internal counter of the RS directive to 
                  a specified value.

        RS      - Assign a value to a symbol; a bit like EQU but here
                  the value assigned is taken from an internal counter,
                  and after the assignation this counter is increased
                  by the amount specified in the RS directive.
                  This is a very handy way of defining structure member
                  offsets, here's a small example:

                      ; C:
                      ; --
                      ; struct {
                      ;    short p_x;
                      ;    short p_y;
                      ;    byte p_color;
                      ; } pixel;
                      ;
                      ; ASM:
                      ; ----

                              .rsset $0  ; set the initial value of RS counter
                      P_X     .rs 2
                      P_Y     .rs 2
                      P_COLOR .rs 1

                  You can later use these symbols as offsets in a 'pixel'
                  struct:

                              ldy #P_COLOR
                              lda [pixel_ptr],Y

        MACRO   - Start a macro definition.

        ENDM    - End a macro definition.

        PROC         - ...

        ENDP         - ...

        PROCGROUP    - ...

        ENDPROCGROUP - ...

        INCBIN  - Include a binary file at the current location. If the file
                  is bigger than a ROM bank, as many successive banks as
                  necessary will be used.

        INCLUDE - Include a source file at the current location.
                  Up to 7 levels are possible.

        INCCHR  - Extract a part of a PCX file and convert it into NES
                  4-color 8x8 graphic characters. Three syntaxes are
                  possible :

                  INCCHR "pic.pcx"

                      Without any additional parameters, the command
                      convert the whole PCX file.

                  INCCHR "pic.pcx",32,4

                      Tell the assembler to convert only 4 rows
                      of 32 characters (a character size is 8x8).

                  INCCHR "pic.pcx",48,16,32,4

                      Same as above but start extracting characters
                      from coordinate 48,16 (in pixels).

        DEFCHR  - Define a character tile (8x8 pixels). The directive takes
                  8 arguments (stored as 32-bit values of 8 nybbles each),
                  one argument for each row of pixel data. This directive
                  takes also care to reorganize the pixel data to the NES
                  required bit format. Note that only color indexes 0 to 3
                  can be used, as the NES tiles are only 4-color. An error
                  will be generated if you try to use more colors.

                      zero:   .defchr  $00111110,\
                                       $01000011,\
                                       $01000101,\
                                       $01001001,\
                                       $01010001,\
                                       $01100001,\
                                       $00111110,\
                                       $00000000

        ZP      - Select the Zero-Page section ($0000-$00FF).

        BSS     - Select the RAM section ($0200-$07FF).

        CODE    - Select the program code section.

        DATA    - Select the program data section.

                  Note: In ZP and BSS sections you can only allocate storage,
                  ----  you can *not* store initial values.

        IF      - Conditional assembly directive. This directive will evaluate
                  the supplied expression and then turn conditional assembly
                  on or off depending on the result. If the result is null
                  conditional assembly is turned off, and on if the result is
                  non null.
        IFDEF
        IFNDEF  - These directives allow conditional assembly depending on
                  whether a label is defined or not.

        ELSE    - Toggle conditional assembly on to off, or vice verca.

        ENDIF   - Terminate the current level of conditional assembly.
                  Report an error if the number of IF's and ENDIF's doesn't
                  match.

        FAIL    - When the assembler encounters this directive, it aborts
                  the compilation. Can be used within a macro for argument
                  error detection.

        INESPRG - Specifies the number of 16k prg banks.

        INESCHR - Specifies the number of 8k chr banks.

        INESMAP - Specifies the NES mapper used.

        INESMIR - Specifies VRAM mirroring of the banks. Refer to iNES header
                  document (neshdr20.txt).


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