GFA tricks & tips - Allocate global memory

Allocate global memory in GFA -Code and info from Ulli Gruszka, Thomas Binder and Lonny Pursell

To allocate global memory that will be used by other applications than your own (AV-protocol, BubbleGEM, etc.) you cannot use the standard MALLOC() but should instead implement these routines supplied by Ulli Gruszka of RUN! Software.

Code to allocate global memory, by Ulli Gruszka (snipped from a thread in CSAS) and later tweaked by Lonny Pursell to allow the programmer to determine what type of memory to allocate.

Call this function once somewhere in your startup code:

  mxmask%=@mxmask
 
 FUNCTION mxmask
    $F%
    IF GEMDOS(68,L:-1,0)=-32  
      RETURN 0
    ELSE IF GEMDOS(290,-1)=-32
      RETURN 3
    ELSE
      RETURN -1
    ENDIF
   ENDFUNC

Call this function if you need memory which will be used by other applications (AV-protocol, BubbleGEM)

bubblebuf%=@mxalloc_global(256,3)

FUNCTION mxalloc_global(amount%,mode&)
$F%
' mode& must be one of the following:
' 0 = ST-RAM only
' 1 = TT-RAM only
' 2 = EITHER, ST-RAM prefered
' 3 = EITHER, TT-RAM prefered
' 
  IF mxmask%<>0
    mode&=OR(mode&,&X100000)
    RETURN GEMDOS(68,L:amount%,mode& AND mxmask%)
  ELSE
    RETURN MALLOC(amount%)
  ENDIF
ENDFUNC

Explanation of the problem, by Thomas Binder (snipped from the same thread in CSAS)

There's a problem on TT and Falcon TOS: Both crash or exhibit other strange behaviour when Mxalloc() is called with memory protection flags. Thus, the code Ulli provided ensures that the memory protection flags are masked off before a call to Mxalloc() is being made when there's no memory protection.

Note that the code doesn't actually test for memory protection, but for the existance of the Sysconf()-call. This is a GEMDOS call present in all versions of MiNT supporting memory protection, but not in TOS or MagiC. Andreas Kromke agreed that - if he implemented memory protection - MagiC would get this call, too.

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