680x0:Opening a library

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This is a example on how to open a library:
(with the Library Vector Offsets added so you won't need to use any includes yet)

OldOpenLibrary = -408 ; OldOpenLibrary(libName)(A1) OpenLibrary = -552 ; OpenLibrary(libName,version)(A1,D0) CloseLibrary = -414 ; CloseLibrary(library)(A1)

move.l $4.w,a6 ; Get the value at position $4 in memory ; This value is the base of exec.library

lea LibName(pc),a1 ; libName must be in A1 moveq #0,d0 ; version must be in D0 jsr OpenLibrary(a6) ; Call the OpenLibrary function

; OpenLibrary looks if the library is in memory (or ROM) ; and loads it if nessesary. ; Then it returns the base of the requested library in d0

move.l d0,libbase ; Store the base

; You can access function in a library with this base, ; like we called OpenLibrary() with exec.library's base.

move.l d0,a6  ; move to a6, since d0 can't be used for addresses
jsr SomeFunction(a6)

; Now close the library we opened move.l $4.w,a6  ; Get exec.library's base again move.l libbase,a1 ; Get the base of the library we want to close jsr CloseLibrary(a6)


libname: dc.b 'dos.library',0 libbase: dc.l $00000000

Notes (important):

  • ...a6
  • ...scratch registers

Notes on optimizing:

    • use 'move.l $4.w,a6' instead of 'move.l $4,a6'
    • use 'moveq' if the version you require is lower than 128
    • if you want to save on bytes you can reuse libname to store your libbase
    • There's also a function OldOpenLibrary doesn't have the library version check. If you are desperate you could use OldOpenLibrary and save a few bytes by not needing a moveq/move.l #version,d0. Commodore didn't want anyone to use this, it would be removed, but it never happened and removing it would probably break too many programs.