93 lines
1.3 KiB
NASM
93 lines
1.3 KiB
NASM
; mmap
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;
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; Block device that maps to memory.
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;
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; *** DEFINES ***
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; MMAP_START: Memory address where the mmap begins
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; *** VARIABLES ***
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MMAP_PTR .equ MMAP_RAMSTART
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MMAP_RAMEND .equ MMAP_PTR+2
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; *** CODE ***
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mmapInit:
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xor a
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ld (MMAP_PTR), a
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ld (MMAP_PTR+1), a
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ret
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; Increase mem pointer by one
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_mmapForward:
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ld hl, (MMAP_PTR)
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inc hl
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ld (MMAP_PTR), hl
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ret
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; Returns absolute addr of memory pointer in HL.
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_mmapAddr:
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push de
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ld hl, (MMAP_PTR)
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ld de, MMAP_START
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add hl, de
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jr nc, .end
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; we have carry? out of bounds, set to maximum
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ld hl, 0xffff
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.end:
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pop de
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ret
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; if out of bounds, will continually return the last char
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; TODO: add bounds check and return Z accordingly.
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mmapGetC:
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push hl
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call _mmapAddr
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ld a, (hl)
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call _mmapForward
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cp a ; ensure Z
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pop hl
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ret
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mmapPutC:
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push hl
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call _mmapAddr
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ld (hl), a
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call _mmapForward
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pop hl
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ret
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mmapSeek:
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cp 1
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jr z, .forward
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cp 2
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jr z, .backward
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cp 3
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jr z, .beginning
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cp 4
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jr z, .end
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; all other modes are considered absolute
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jr .set ; for absolute mode, HL is already correct
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.forward:
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ld de, (MMAP_PTR)
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add hl, de
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jr nc, .set
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; we have carry? out of bounds, set to maximum
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ld hl, 0xffff
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jr .set
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.backward:
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; TODO - subtraction are more complicated...
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jr .set
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.beginning:
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ld hl, 0
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jr .set
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.end:
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ld hl, 0xffff-MMAP_START
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.set:
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ld (MMAP_PTR), hl
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ret
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mmapTell:
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ld hl, (MMAP_PTR)
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ret
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