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Use uppercase non-struct constants for BPB

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This commit is contained in:
Nero 2020-10-25 09:15:33 +00:00
parent dc6035fe9d
commit 50aa6e4eec
4 changed files with 47 additions and 95 deletions
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30
boot/fat.asm
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@ -19,7 +19,7 @@ bootsect: equ 0x7C00 ; our origin before reloc
times ( 0x0B - ($-$$) ) db 0
params: times bpb_size db 0
bpb: times BPBSIZ4 db 0
; Area for BPB
times ( 0x3E - ($-$$) ) db 0
@ -54,15 +54,15 @@ read: push ax
push dx
xchg ax, bx
mov al, byte [bp+bpb.heads]
mul byte [bp+bpb.tracksectors]
mov al, byte [bp+BPBNOS]
mul byte [bp+BPBSPT]
xchg ax, bx
; dx:ax = lba
div word bx
xchg ax, dx
; dx = cylinder, ax = head * tracksectors + sector
div byte [bp+bpb.tracksectors]
div byte [bp+BPBSPT]
; dx = cylinder, al = head, ah = sector
xchg dl, dh
ror dl, 1
@ -92,7 +92,7 @@ read: push ax
loop read
ret
rootdirsects: mov bx, [bp+bpb.direntries]
rootdirsects: mov bx, [bp+BPBRDE]
mov cl, 4
shr bx, cl ; 32 bytes per entry
ret
@ -103,16 +103,16 @@ offset_cluster: ; add offset of cluster data area to DX:AX
adc dx, 0
offset_rootdir: ; add length of fat table times number of fats
xor ch, ch
mov cl, byte [bp+bpb.fatnumber]
.loop: add ax, [bp+bpb.fatsectors]
mov cl, byte [bp+BPBFN]
.loop: add ax, [bp+BPBFS]
adc dx, 0
loop .loop
offset_fat: ; add reserved sectors
add ax, [bp+bpb.reservedsects]
add ax, [bp+BPBRSC]
adc dx, 0
offset_part: ; add partition offset
add ax, [bp+bpb.sectoroffset]
add dx, [bp+bpb.sectoroffset+2]
add ax, [bp+BPBHS]
add dx, [bp+BPBHS]
ret
resetbuf: ; DS = ES
@ -127,7 +127,7 @@ resetbuf: ; DS = ES
xor dx, dx
ret
main: mov bp, params
main: mov bp, bpb
mov [bp-1], dl
; load root directory
@ -140,7 +140,7 @@ main: mov bp, params
; search for file
pop bx
mov cx, [bp+bpb.direntries]
mov cx, [bp+BPBRDE]
.loop: push cx
mov si, filename
mov di, bx
@ -156,7 +156,7 @@ main: mov bp, params
call resetbuf
push di
call offset_fat
mov cx, [bp+bpb.fatsectors]
mov cx, [bp+BPBFS]
call read
; fetch cluster numbers (FAT12-specific)
@ -189,10 +189,10 @@ readfat: stosw
loadclus: lodsw
sub ax, 2
jc .jump
mul byte [bp+bpb.clustersects]
mul byte [bp+BPBSC]
call offset_cluster
xor cx, cx
mov cl, [bp+bpb.clustersects]
mov cl, [bp+BPBSC]
call read
jmp loadclus

12
boot/mbr.asm
View file

@ -10,7 +10,7 @@
%include "inc/bpb.asm"
%define params bs+0x0B
%define bpb bs+0x0B
cpu 8086
org 0x0600
@ -72,11 +72,11 @@ main: ; find active partition
; FAT bpb has "bytes per sector" at this place
; we support only 512 byte sectors anyways
cmp word [params+bpb.sectorsize], 512
cmp word [bpb+BPBSS], 512
jne chain
; Media descriptor byte is never smaller than 0xF0
cmp byte [params+bpb.mediadesc], 0xF0
cmp byte [bpb+BPBMD], 0xF0
jc chain
; ask BIOS what our disk geometry is
@ -92,17 +92,17 @@ main: ; find active partition
; update sectors per track
xor ax, ax
mov al, cl
mov [params+bpb.tracksectors], ax
mov [bpb+BPBSPT], ax
; update number of sides
xor ax, ax
mov al, dh
mov [params+bpb.heads], ax
mov [bpb+BPBNOS], ax
; update partition offset
push si
add si, 0x08
mov di, params+bpb.sectoroffset
mov di, bpb+BPBHS
movsw
movsw
pop si