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collapseos/parts/mmap.asm
Virgil Dupras a27da6f41a add mmap part
This also introduces the "seek" shell command.
2019-04-16 08:36:26 -04:00

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774 B
NASM

; mmap
;
; Block device that maps to memory.
;
; *** DEFINES ***
; MMAP_START: Memory address where the mmap begins
; *** VARIABLES ***
MMAP_PTR .equ MMAP_RAMSTART
MMAP_RAMEND .equ MMAP_PTR+2
; *** CODE ***
; Increase mem pointer by one
_mmapForward:
ld hl, (MMAP_PTR)
inc hl
ld (MMAP_PTR), hl
ret
; Returns absolute addr of memory pointer in HL.
_mmapAddr:
push de
ld hl, (MMAP_PTR)
ld de, MMAP_START
add hl, de
jr nc, .end
; we have carry? out of bounds, set to maximum
ld hl, 0xffff
.end:
pop de
ret
; if out of bounds, will continually return the last char
mmapGetC:
push hl
call _mmapAddr
ld a, (hl)
call _mmapForward
pop hl
ret
mmapPutC:
push hl
call _mmapAddr
ld (hl), a
call _mmapForward
pop hl
ret
mmapSeek:
ld (MMAP_PTR), hl
ret