6502basiccompiler/arch/6502/__sandbox__/library-asm/_2_converting/heapinit.asm

; vim: ts=4:et:sw=4:
; Copyleft (K) by Jose M. Rodriguez de la Rosa
;  (a.k.a. Boriel)
;  http://www.boriel.com
;
; This ASM library is licensed under the BSD license
; you can use it for any purpose (even for commercial
; closed source programs).
;
; Please read the BSD license on the internet

; ----- IMPLEMENTATION NOTES ------
; The heap is implemented as a linked list of free blocks.

; Each free block contains this info:
;
; +----------------+ <-- HEAP START
; | Size (2 bytes) |
; |        0       | <-- Size = 0 => DUMMY HEADER BLOCK
; +----------------+
; | Next (2 bytes) |---+
; +----------------+ <-+
; | Size (2 bytes) |
; +----------------+
; | Next (2 bytes) |---+
; +----------------+   |
; | <free bytes...>|   | <-- If Size > 4, then this contains (size - 4) bytes
; | (0 if Size = 4)|   |
; +----------------+ <-+
; | Size (2 bytes) |
; +----------------+
; | Next (2 bytes) |---+
; +----------------+   |
; | <free bytes...>|   |
; | (0 if Size = 4)|   |
; +----------------+   |
;   <Allocated>        | <-- This zone is in use (Already allocated)
; +----------------+ <-+
; | Size (2 bytes) |
; +----------------+
; | Next (2 bytes) |---+
; +----------------+   |
; | <free bytes...>|   |
; | (0 if Size = 4)|   |
; +----------------+ <-+
; | Next (2 bytes) |--> NULL => END OF LIST
; |    0 = NULL    |
; +----------------+
; | <free bytes...>|
; | (0 if Size = 4)|
; +----------------+


; When a block is FREED, the previous and next pointers are examined to see
; if we can defragment the heap. If the block to be breed is just next to the
; previous, or to the next (or both) they will be converted into a single
; block (so defragmented).


;   MEMORY MANAGER
;
; This library must be initialized calling __MEM_INIT with
; HL = BLOCK Start & DE = Length.

; An init directive is useful for initialization routines.
; They will be added automatically if needed.

#init "__MEM_INIT"


; ---------------------------------------------------------------------
;  __MEM_INIT must be called to initalize this library with the
; standard parameters
; ---------------------------------------------------------------------
__MEM_INIT: ; Initializes the library using (RAMTOP) as start, and
                     ;- ld hl, ZXBASIC_MEM_HEAP  ; Change this with other address of heap start
                     ;- ld de, ZXBASIC_HEAP_SIZE ; Change this with your size

; ---------------------------------------------------------------------
;  __MEM_INIT2 initalizes this library
; Parameters:
;   HL : Memory address of 1st byte of the memory heap
;   DE : Length in bytes of the Memory Heap
; ---------------------------------------------------------------------
__MEM_INIT2:
; HL as TOP
                     ;- PROC
                     ;- dec de
                     ;- dec de
                     ;- dec de
                     ;- dec de        ; DE = length - 4; HL = start
; This is done, because we require 4 bytes for the empty dummy-header block
eor z80_a            ;- xor a
lda z80_a            ;- ld (hl),a
ldy #$00
sta (z80_hl),y
inc z80_l            ;- inc hl
bne *+4
inc z80_h
lda z80_a            ;- ld (hl),a ; First "free" block is a header: size=0, Pointer=&(Block) + 4
ldy #$00
sta (z80_hl),y
inc z80_l            ;- inc hl
bne *+4
inc z80_h
lda z80_h            ;- ld b,h
sta z80_b
lda z80_l            ;- ld c,l
sta z80_c
inc z80_c            ;- inc bc
bne *+4
inc z80_b
inc z80_c            ;- inc bc      ; BC = starts of next block
bne *+4
inc z80_b
lda z80_c            ;- ld (hl),c
ldy #$00
sta (z80_hl),y
inc z80_l            ;- inc hl
bne *+4
inc z80_h
lda z80_b            ;- ld (hl),b
ldy #$00
sta (z80_hl),y
inc z80_l            ;- inc hl      ; Pointer to next block
bne *+4
inc z80_h
lda z80_e            ;- ld (hl),e
ldy #$00
sta (z80_hl),y
inc z80_l            ;- inc hl
bne *+4
inc z80_h
lda z80_d            ;- ld (hl),d
ldy #$00
sta (z80_hl),y
inc z80_l            ;- inc hl      ; Block size (should be length - 4 at start); This block contains all the available memory
bne *+4
inc z80_h
lda z80_a            ;- ld (hl), a ; NULL (0000h) ; No more blocks (a list with a single block)
ldy #$00
sta (z80_hl),y
inc z80_l            ;- inc hl
bne *+4
inc z80_h
lda z80_a            ;- ld (hl),a
ldy #$00
sta (z80_hl),y
                     ;- ld a,201
                     ;- ld (__MEM_INIT), a; "Pokes" with a RET so ensure this routine is not called again
rts                  ;- ret
                     ;- ENDP