150 lines
2.5 KiB
Z80 Assembly
150 lines
2.5 KiB
Z80 Assembly
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.global set_frame
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.global get_frame
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.global clear_frame
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.global vmem_init
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.global vmem_mapping_card
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.global vmem_mapping_bank_low
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.global vmem_mapping_bank_high
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.global pmap_set
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.global pmap_load
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; map a RAM frame into memory
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; C contains the page to map
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; B contains the card # to use
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; DE contains the bank # in the card
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; The contents of A, IX and C are destroyed
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set_frame:
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ld a, c
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ld (card_set+2), a
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ld (low_set+2), a
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ld (high_set+2), a
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ld ix, vmem_mapping_card
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card_set: ld (ix+0), b
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ld ix, vmem_mapping_bank_low
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low_set: ld (ix+0), e
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ld ix, vmem_mapping_bank_high
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high_set: ld (ix+0), d
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ld a, e
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out (c), a
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ld a, c
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or 0x20
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ld c, a
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ld a, d
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or 0x80
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out (c), a
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ret
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; Get the RAM frame a page is mapped to
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; C contains the page to get
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; B will contain the card #
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; DE will contain the bank # in the card
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; The contents of A, IX are destroyed
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; If the page is unmapped, C will be 0 and DE will contain garbage
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get_frame:
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ld a, c
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ld (vgf_card_get+2), a
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ld (vgf_low_get+2), a
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ld (vgf_high_get+2), a
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ld ix, vmem_mapping_card
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vgf_card_get: ld b, (ix+0)
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ld ix, vmem_mapping_bank_low
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vgf_low_get: ld e, (ix+0)
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ld ix, vmem_mapping_bank_high
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vgf_high_get: ld d, (ix+0)
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ret
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; Unmaps a memory page
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; C contains the page to unmap
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; The contents of A, BC, DE, and IX are destroyed
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clear_frame:
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call get_frame
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ld a, c
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ld (vcf_card_set+2), a
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ld ix, vmem_mapping_card
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vcf_card_set: ld (ix+0), 0
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xor a
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out (c), a
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ld a, c
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or 0x20
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ld c, a
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xor a
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out (c), a
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ret
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; Loads a pagemap pointed to by IX
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; The contents of A, BC, DE, and IX are destroyed
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pmap_load:
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ld c, 0
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pmap_load_loop:
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push bc
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push ix
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call clear_frame
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pop ix
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pop bc
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ld b, (ix+0)
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ld e, (ix+1)
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ld d, (ix+2)
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push bc
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push ix
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call set_frame
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pop ix
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pop bc
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inc ix
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inc ix
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inc ix
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inc c
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ld a, c
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cp 12
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jp nz, pmap_load_loop
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ret
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; Stores the pagemap in the memory pointed to by IX
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; The contents of A, BC, DE, and IX are destroyed
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pmap_set:
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ld c, 0
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pmap_set_loop:
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push ix
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call get_frame
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pop ix
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ld (ix+0), b
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ld (ix+1), e
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ld (ix+2), d
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inc ix
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inc ix
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inc ix
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inc c
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ld a, c
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cp 12
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jp nz, pmap_set_loop
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ret
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RAM_TYPE equ 2
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; Initializes the virtual memory manager
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vmem_init:
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ld b, RAM_TYPE
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call find_first_card
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ld a, l
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ld c, 15
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ld b, 0
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ld de, vmem_mapping_card
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ld h, d
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ld l, e
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inc de
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ld (hl), a
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ldir
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ld ix, vmem_mapping_bank_low+15
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ld b, 15
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vmem_init_loop:
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ld (ix+0), b
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dec ix
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djnz vmem_init_loop
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ret
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vmem_mapping_card: .ds.b 16, 0
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vmem_mapping_bank_low: .ds.b 16, 0
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vmem_mapping_bank_high: .ds.b 16, 0
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