Assembly and Files under ProDOS

RTK, last update: 23-Jul-97

Assembly and Files

   This file is specific to the Apple II series of computers running ProDOS.  It
   explains how to make simple use of disk files via assembly language.

   1. MLI and commands
   2. Detailed command descriptions
   3. Programming example
MLI and commands

   Most disk access from within an Apple II assembly language program 
   uses the machine language interface supplied by the ProDOS operating 
   system.  Commands consist of a call to $BF00 followed by a table of 
   command parameters.  If ProDOS returns a value it is returned in a 
   location within this table.  MacQForth implements a useful subset of 
   the standard ProDOS commands.  The general form of a command is:
           JSR $BF00           ;  call ProDOS to do the command
           (execution returns to here when finished)
   If an error happens, the carry flag is set and the accumulator 
   contains the error code.  MacQForth returns 0 if no error or the 
   absolute value of the corresponding Macintosh file error number if an 
   error happened.
   The contents of the parameter table vary from command to command, but 
   a general form is:
   So, a possible assembly language calling sequence to read some data 
   from an open file (file 0) might be:
            ldx #$00
            ldy #$10        
            sty params+4
            stx params+5    ; setup number of bytes to read (16)
            jsr $BF00       ; call ProDOS
            .BYTE $CA       ; ProDOS command number = CA (read)
            .WORD params    ; address of parameter table, lo/hi
            bcs error       ; carry set, error
     params .BYTE $04       ; number of parameters for a read
            .BYTE $00       ; file reference number, 0, 1, 2 in MacQForth
            .WORD BUFFER    ; pointer to data buffer
            .WORD $0000     ; requested number of bytes to read, fill in
            .WORD $0000     ; number actually read, returned by ProDOS
   The following ProDOS commands are available and their parameters are 
   outlined below:
          $C0  =  create a new file
          $C1  =  destroy an existing file
          $C4  =  get file info (a dummy command, do not use)
          $C8  =  open a file (reference numbers 0, 1, or 2)
          $CA  =  read from a file
          $CB  =  write to a file
          $CC  =  close a file
          $CE  =  position file marker
          $65  =  bye, cause MacQForth to quit, use to quit the application
                  from within an assembly language program

   Note: Do not use "/" as the directory separator.  Instead, use ":" which 
   is the normal Mac separator.  Remember that pathnames are stored as 
   length/text.  So, the pathname for the file "ABC" is stored (in decimal) 
   as 3,65,66,67. (Minus commas, of course!)

Detailed command descriptions

   Command parameters marked as _required_ are necessary for MacQForth, 
   those marked as _ignored_ are not.  Any value can be in the _ignored_ 
   field.  If a parameter is returned it is indicated as a (result) and 
   space must be made for the value.
   ** Create a new file
      command number $C0
              0    (number-of-parameters) (7)      _required_
             +1    (pointer to pathname)           _required_
             +3    (access code)                   _ignored_
             +4    (file type code)                _ignored_
             +5    (auxilliary type code)          _ignored_
             +7    (storage type)                  _ignored_
             +8    (date of creation)              _ignored_
             +10   (time of creation)              _ignored_
   ** Destroy an existing file
      command number $C1
             0     (number-of-parameters) (1)      _required_
            +1     (pointer to pathname)           _required_
   ** Open an existing file
      command number $C8
             0     (number-of-parameters) (3)      _required_
            +1     (pointer to pathname)           _required_
            +3     (pointer to i/o buffer)         _required_**
            +5     (reference number, 0, 1, 2)     _required_ (result)
            ** MacQForth is trailored to running QForth.  Therefore,
               you can use at most three files corresponding to reference
               numbers 0, 1, and 2.  MacQForth determines which file
               QForth wants to use by the address of this buffer.  The
               buffer itself is unused but it _must_ be one of the
               following addresses, in lo/hi format,
                   File 0   =   00:A6
                   File 1   =   00:A2
                   File 2   =   00:9E
   ** Read from an open file
      command number $CA
             0     (number-of-parameters) (4)      _required_
            +1     (file reference number)         _required_
            +2     (pointer to data buffer)        _required_
            +4     (requested number of bytes)     _required_
            +6     (number actually read)          _required_ (result)
   ** Write to an open file
      command number $CB
             0     (number-of-parameters) (4)      _required_
            +1     (file reference number)         _required_
            +2     (pointer to data buffer)        _required_
            +4     (requested number of bytes)     _required_
            +6     (number actually written)       _required_ (result)
   ** Close an open file
      command number $CC
             0      (number-of-parameters) (1)     _required_
            +1      (file reference number)        _required_
   ** Position file marker within an open file
      command number $CE
             0      (number-of-parameters) (2)     _required_
            +1      (file reference number)        _required_
            +2      (file position, *3* bytes)     _required_
   ** Bye
      command number $65
             0      (number-of-parameters) (4)     _ignored_
            +1      (quit type code)               _ignored_
            +2      (pointer to quit code)         _ignored_
            +4      (a reserved value)             _ignored_
            +5      (a reserved pointer)           _ignored_

Programming example

   A simple programming example to create a new file named "ABC" and 
   write some text to it.  Also in FILE.S in the DEMO folder.
   ; MakeFile -- creates a file and writes some data. Ignores errors.
    *= $300
   ; create the file "ABC"
    lda #$01           ; setup for 'create'
    sta PARAMS      
    lda #<NAME          ; low byte of name address
    sta PARAMS+1
    lda #>NAME         ; high byte of name address
    sta PARAMS+2
    lda #$C0           ; create command
    sta MLI+3          ; put in table
    jsr MLI            ; create the file
   ; open the file
    lda #$03
    sta PARAMS         ; adjust number of parameters, name already set
    lda #$00
    sta PARAMS+3
    lda #$A6
    sta PARAMS+4       ; use file 0
    lda #$C8           ; open command
    sta MLI+3
    jsr MLI            ; open the file
   ; write to the file
    lda #$04
    sta PARAMS
    lda PARAMS+5       ; get reference number returned by open
    sta PARAMS+1       ; and put in for write
    sta REF            ; and save for close
    lda #<STRING        
    sta PARAMS+2       ; pointer to data
    lda #>STRING
    sta PARAMS+3
    lda #$05           ; number of bytes to write
    sta PARAMS+4
    lda #$00
    sta PARAMS+5
    lda #$CB           ; write command
    sta MLI+3
    jsr MLI            ; write the data
   ; close the file
    lda #$01           
    sta PARAMS
    lda REF            ; put in reference number
    sta PARAMS+1
    lda #$CC           ; close command
    sta MLI+3
    jsr MLI            ; close the file
    rts                ; and end
   ; call MLI
   MLI jsr $BF00       ; call ProDOS
    .byte $00          ; command number
    .word PARAMS       ; address of parameter table
   ; data
   NAME .byte 3,"ABC"        ; name of the file with length
   STRING .byte "Hello",0    ; data to write
   REF .byte $00             ; ProDOS reference number
   PARAMS .dbyt $0000        ; ProDOS parameter table
    .dbyt $0000
    .dbyt $0000
    .dbyt $0000

Last update: 30-Jan-00
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