.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: 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