*  ==============================================================
*  IMAGE PROCESSOR v2 ExtDump format information, by Dilwyn Jones
*  ==============================================================
*  Shows how to create a machine code extension to add a screen
*  dump to your specification outside of Image Processor 2.
*
*  Created with "Computer One" assembler & editor, 4 August 1992
*  Assembled version is DUMMY_ExtDump_bin on the disk, which you
*  can LRESPR prior to using Image Processor if required.
*  The assembled version on the disk is just 34 bytes long,if you
*  want to use RESPR/LBYTES/CALL instead:-
*    edmp = RESPR(34)
*    LBYTES flp1_DUMMY_ExtDump_cde,edmp
*    CALL edmp
*
*  It is also possible to use QLiberator to compile a BASIC
*  program as an 'external' (using the $$external directive)
*  if preferred, although that will be a much larger piece
*  of compiled code (and slower), but simpler to write!
*
*  This creates a BASIC extension called 'ExtDump' to act as
*  a 'dummy' extension (which simply does nothing except
*  preventing an error if no External Dump routine is
*  present!
*
*  Image Processor 2 drives the external dump as a normal BASIC
*  extension and supplies 5 parameters, as follows:
*  ExtDump printer$,address,invert_or_not,passes%,mode%
*  (1) printer$ is a string with the printer channel device name
*      e.g. ser1
*  (2) address is a floating point value with the address of the
*      base of the screen. This is actually a copy of the screen
*      in memory and will not be at the standard screen #1 or #2
*      video memory locations. Although the address is sent as a
*      floating point number,it is recoverable as a long word by
*      fetching the parameter with CA.GTLIN to make life easier.
*  (3) Invert_or_not is sent as a floating point,but is actually
*      only ever 0 (don't invert) or 1 (invert, please), and can
*      be recovered as an integer if required.It would have been
*      easier if this was sent as an integer,but it's a floating
*      point value inside Image Processor, for internal reasons.
*      Although you should fetch this parameter value to be able
*      to get at the later parameters, you can ignore it and let
*      your routine 'do its own thing'.
*  (4) Passes% is sent as a 16 bit integer and is a value from 0
*      to 9, with the number of passes of the print head to make
*      for each line of printing. As with (3) above, you can, if
*      you want to, ignore its value and let your routine do its
*      own thing.
*  (5) Mode% This is a 16 bit value containing either 4 (MODE 4)
*      or 8 (screen MODE 8),  to tell you the screen mode of the
*      picture to be printed. You are advised not to ignore this
*      since it is not possible to check the screen mode of this
*      picture any other way  (the QL 's current display mode is
*      not necessarily the same).   At the time of writing this,
*      no other values are sent apart from 4 or 8 (e.g.Thor MODE
*      12 is not supported), although this may change later if a
*      new display adaptor device becomes  available  and  Image
*      Processor is altered to work with new display modes.
*
*  CODE TO LINK IN BASIC EXTENSION:-

        move.w  $110,a0         ;BP.INIT vector
        lea     define,a1       ;pointer to definition table
        jsr     (a0)            ;call vector to link in extensions
        rts                     ; and go back to SuperBASIC

define  dc.w    1               ;approximately 1 new procedure
        dc.w    extdmp-*        ;where is it?
        dc.b    7,"ExtDump"     ;name of the extension
        dc.w    0               ;end of new procedures list
        dc.w    0               ;approximately 0 functions
        dc.w    0               ;end of functions list

* install your machine code here  -  all I've done is to put in an
* instruction to clear register d0 to prevent an error report & an
* immediate  RTS instruction to jump back to the calling routines,
* without doing anything except preventing an error by being here!


extdmp  clr.w   d0              ;make sure of no error on return!
        rts                     ;go back to the calling program.