.global set_frame
.global get_frame
.global clear_frame
.global vmem_init
.global vmem_mapping_card
.global vmem_mapping_bank_low
.global vmem_mapping_bank_high
.global pmap_set
.global pmap_load

; map a RAM frame into memory
; C contains the page to map
; B contains the card # to use
; DE contains the bank # in the card 
; The contents of A, IX and C are destroyed
set_frame:
  push bc
  push de
  call clear_frame
  pop de
  pop bc
  ld a, c
  ld (card_set+2), a
  ld (low_set+2), a
  ld (high_set+2), a
  ld ix, vmem_mapping_card
  card_set: ld (ix+0), b
  ld ix, vmem_mapping_bank_low
  low_set: ld (ix+0), e
  ld ix, vmem_mapping_bank_high
  high_set: ld (ix+0), d
  ld a, e 
  out (c), a 
  ld a, c
  or 0x20
  ld c, a
  ld a, d
  or 0x80
  out (c), a
  ret

; Get the RAM frame a page is mapped to 
; C contains the page to get
; B will contain the card #
; DE will contain the bank # in the card
; The contents of A, IX are destroyed
; If the page is unmapped, C will be 0 and DE will contain garbage
get_frame:
  ld a, c
  ld (vgf_card_get+2), a
  ld (vgf_low_get+2), a
  ld (vgf_high_get+2), a
  ld ix, vmem_mapping_card
  vgf_card_get: ld b, (ix+0)
  ld ix, vmem_mapping_bank_low
  vgf_low_get: ld e, (ix+0)
  ld ix, vmem_mapping_bank_high
  vgf_high_get: ld d, (ix+0)
  ret

; Unmaps a memory page
; C contains the page to unmap
; The contents of A, BC, DE, and IX are destroyed
clear_frame:
  call get_frame
  ld a, c
  ld (vcf_card_set+2), a
  ld ix, vmem_mapping_card
  vcf_card_set: ld (ix+0), 0
  xor a
  out (c), a
  ld a, c
  or 0x20
  ld c, a
  xor a
  out (c), a
  ret

; Loads a pagemap pointed to by IX
; The contents of A, BC, DE, and IX are destroyed
pmap_load:
ld c, 0
pmap_load_loop:
push bc
push ix
call clear_frame
pop ix
pop bc
ld b, (ix+0)
ld e, (ix+1)
ld d, (ix+2)
push bc
push ix
call set_frame
pop ix
pop bc
inc ix
inc ix
inc ix
inc c
ld a, c
cp 12
jp nz, pmap_load_loop
ret

; Stores the pagemap in the memory pointed to by IX
; The contents of A, BC, DE, and IX are destroyed
pmap_set:
ld c, 0
pmap_set_loop:
push ix
call get_frame
pop ix
ld (ix+0), b
ld (ix+1), e
ld (ix+2), d
inc ix
inc ix
inc ix
inc c
ld a, c
cp 12
jp nz, pmap_set_loop
ret

RAM_TYPE equ 2

; Initializes the virtual memory manager
vmem_init:
ld b, RAM_TYPE
call find_first_card
ld a, l
ld c, 15 
ld b, 0
ld de, vmem_mapping_card
ld h, d
ld l, e
inc de
ld (hl), a
ldir
ld ix, vmem_mapping_bank_low+15
ld b, 15
vmem_init_loop:
ld (ix+0), b
dec ix
djnz vmem_init_loop
ret



vmem_mapping_card: .ds.b 16, 0
vmem_mapping_bank_low: .ds.b 16, 0
vmem_mapping_bank_high: .ds.b 16, 0