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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 cmp al, 0x0D
jnz .loop jnz .loop
push dx
call dinit
pop dx
cmp dl, 0x80 cmp dl, 0x80
jc .k jc .k
sub dl, (0x80-2) sub dl, (0x80-2)

49
kernel/drive.asm
View File

@ -28,6 +28,45 @@ bpb: resb BPBSIZ4
section .text 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 ; log in drive
; currently only supports 18 sectors 2 heads floppies ; currently only supports 18 sectors 2 heads floppies
; IN dl drive number ; IN dl drive number
@ -46,6 +85,8 @@ logdrv: ; dont do anything if drive already selected
mov [dsknum], dl mov [dsknum], dl
; save info for bios ; save info for bios
mov [biosnum], dl mov [biosnum], dl
; reset dpt to defaults
call rstdpt
; set default geometry (1.44 MB floppy) ; set default geometry (1.44 MB floppy)
mov word [bpb+BPBNOS], 2 mov word [bpb+BPBNOS], 2
mov word [bpb+BPBSPT], 18 mov word [bpb+BPBSPT], 18
@ -54,10 +95,14 @@ logdrv: ; dont do anything if drive already selected
xor dx, dx xor dx, dx
call mapabs call mapabs
; copy bios parameter block ; 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 di, bpb
mov cx, BPBSIZ4 mov cx, BPBSIZ4
rep movsb rep movsb
; copy SPT to DPT
mov al, [bpb+BPBSPT]
mov [dpt+4], al
; make sure partition offset is forced zero ; make sure partition offset is forced zero
xor ax, ax xor ax, ax
mov [bpb+BPBHS], ax mov [bpb+BPBHS], ax
@ -68,7 +113,7 @@ calchs: ; put sectors per cylinder into bx
mov ax, [bpb+BPBSPT] mov ax, [bpb+BPBSPT]
mul word [bpb+BPBNOS] mul word [bpb+BPBNOS]
mov bx, ax mov bx, ax
; but linear sector num into dx:ax ; put linear sector num into dx:ax
mov ax, [dskseek] mov ax, [dskseek]
mov dx, [dskseek+2] mov dx, [dskseek+2]
; dx:ax = linear count, bx = sectors / cylinder ; dx:ax = linear count, bx = sectors / cylinder