QDOS Internals

The examples below show the use of MM_LNKFR/MEM_REHP to set up a user heap and to return space to the user heap.

Setting up a user heap

We suppose that A6 points to the program's data space and that heapad is the offset to a long word containing the pointer to free space.

        moveq   #MT_ALCHP,d0    ; $18
        move.l  space,d1        ; Number of bytes required.
        moveq   #-1,d2          ; This job
	trap	#1      	; The base address is set in A0
        tst.l   d0
	bne.s	Error_handler	; Oops!
        lea     heapad(a6),a1   ; Set the pointer to the pointer to the user heap
        clr.l   (a1)            ; Set the pointer to zero
        movea.w mm_lnkfr,a2     ; Put the vector in A2 . .
        jsr     (a2)            ; . . and use it
                                ; Now the user heap is set up at A0

space   dc.l    $2000           ; Amount of space needed

Returning space to the user heap

Suppose that buffer(a6) is the pointer to a buffer allocated from the user heap and that buff_len(a6) contains its length. The code shows this buffer being returned to the user heap.

        movea.l buffer(a6),a0   ; Base of space to be freed
        move.l  buff_len(a6),d1 ; Size of space
        lea     heapad(a6),a1   ; Set the pointer to the pointer to the user heap        
        movea.w mm_lnkfr,a2     ; Put the vector in A2 . .
        jsr     (a2)            ; . . and use it