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Support managing floppy parameter table

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This commit is contained in:
Nero 2020-12-22 21:14:16 +00:00
parent f10fa026cf
commit 0a2a0e4659
2 changed files with 51 additions and 2 deletions
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4
boot/kernel.asm
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@ -24,6 +24,10 @@ print_banner: mov si, banner
cmp al, 0x0D
jnz .loop
push dx
call dinit
pop dx
cmp dl, 0x80
jc .k
sub dl, (0x80-2)

49
kernel/drive.asm
View File

@ -28,6 +28,45 @@ bpb: resb BPBSIZ4
section .text
; initial setup for disk i/o
dinit: ; copy previously set DPT to our data area
lds si, [4*0x1E]
mov di, dpt
mov cx, 11
rep movsb
; restore DS
xor ax, ax
mov ds, ax
; set vector
mov word [4*0x1E], dpt
mov word [4*0x1E+2], ds
ret
; restore DPT to default values if possible
; IN dl bios drive number
rstdpt: mov ah, 8
int 0x13
jc .ret
mov ax, es
or ax, di
test ax, ax
jz .ret
; DS:SI = ES:DI
mov ax, es
mov ds, ax
mov si, di
; ES:DI = dpt
xor ax, ax
mov es, ax
mov di, dpt
; do the copy
mov cx, 11
rep movsb
.ret: ; restore DS to 0
xor ax, ax
mov ds, ax
ret
; log in drive
; currently only supports 18 sectors 2 heads floppies
; IN dl drive number
@ -46,6 +85,8 @@ logdrv: ; dont do anything if drive already selected
mov [dsknum], dl
; save info for bios
mov [biosnum], dl
; reset dpt to defaults
call rstdpt
; set default geometry (1.44 MB floppy)
mov word [bpb+BPBNOS], 2
mov word [bpb+BPBSPT], 18
@ -54,10 +95,14 @@ logdrv: ; dont do anything if drive already selected
xor dx, dx
call mapabs
; copy bios parameter block
lea si, [dskbuf+BPBOFF]
; TODO: guess from first byte of FAT if BPB invalid
mov si, dskbuf+BPBOFF
mov di, bpb
mov cx, BPBSIZ4
rep movsb
; copy SPT to DPT
mov al, [bpb+BPBSPT]
mov [dpt+4], al
; make sure partition offset is forced zero
xor ax, ax
mov [bpb+BPBHS], ax
@ -68,7 +113,7 @@ calchs: ; put sectors per cylinder into bx
mov ax, [bpb+BPBSPT]
mul word [bpb+BPBNOS]
mov bx, ax
; but linear sector num into dx:ax
; put linear sector num into dx:ax
mov ax, [dskseek]
mov dx, [dskseek+2]
; dx:ax = linear count, bx = sectors / cylinder