kernel: First steps of calculating drive tab data from BPB
This commit is contained in:
parent
cc3fe6c4ee
commit
352540bd25
|
|
@ -2,9 +2,28 @@
|
|||
org 0x500
|
||||
|
||||
%include "inc/bpb.asm"
|
||||
%include "inc/mbr.asm"
|
||||
%include "inc/dpt.asm"
|
||||
|
||||
; drive table entry
|
||||
struc drive
|
||||
.biosnum: resb 1
|
||||
.flag: resb 1
|
||||
.spc: resw 1
|
||||
.cylinders: resw 1
|
||||
.dpt: resb dpt_size
|
||||
.type: resb 1 ; 12 or 16, depending on FAT type
|
||||
.fat_offset: resd 1 ; offset of fat table
|
||||
.fat_num: resw 1 ; number of fat tables
|
||||
.fat_size: resw 1 ; sectors per fat table
|
||||
|
||||
.dir_offset: resd 1 ; offset of root directory
|
||||
.dir_size: resw 1 ; size of root directory in sectors
|
||||
|
||||
.clus_offset: resd 1 ; offset of clusters
|
||||
.clus_num: resw 1 ; number of clusters
|
||||
.clus_size: resw 1 ; sectors per cluster
|
||||
endstruc
|
||||
|
||||
; kernel stack size in words
|
||||
%define stacksize 512
|
||||
|
||||
|
|
@ -240,6 +259,7 @@ fputc: push ax
|
|||
iret
|
||||
|
||||
%include "kernel/drive.asm"
|
||||
%include "kernel/fat.asm"
|
||||
|
||||
zero: dw 0
|
||||
|
||||
|
|
@ -252,5 +272,5 @@ vects: dw int20h, int21h, retf, retf
|
|||
_end: dw 0x55AA, 0x55AA
|
||||
|
||||
section .bss
|
||||
; stack to be used during init and disk i/o
|
||||
stack: resw stacksize
|
||||
; stack to be used during init and disk i/o
|
||||
stack: resw stacksize
|
||||
|
|
|
|||
|
|
@ -2,15 +2,6 @@ section .bss
|
|||
|
||||
drives: equ 16
|
||||
|
||||
; drive table entry
|
||||
struc drive
|
||||
.biosnum: resb 1
|
||||
.flag: resb 1
|
||||
.spc: resw 1
|
||||
.cylinders: resw 1
|
||||
.dpt: resb dpt_size
|
||||
endstruc
|
||||
|
||||
; ptr into currently selected drive
|
||||
drive_ptr: resw 1
|
||||
|
||||
|
|
|
|||
160
kernel/fat.asm
160
kernel/fat.asm
|
|
@ -1,112 +1,60 @@
|
|||
section .bss
|
||||
section .text
|
||||
|
||||
; the sector numbers have the partition offset already included
|
||||
|
||||
fat_offset:
|
||||
resd 1
|
||||
fat_size:
|
||||
resd 1
|
||||
fat_num: ; a byte would be enough, but i want to work with cx
|
||||
resw 1
|
||||
|
||||
rootdir_offset:
|
||||
resd 1
|
||||
rootdir_size:
|
||||
resw 1
|
||||
|
||||
clusters_offset:
|
||||
resd 1
|
||||
clusters_num:
|
||||
resd 1
|
||||
|
||||
section .text
|
||||
|
||||
load_ts: ; load total number of sectors into DX:AX
|
||||
xor dx, dx
|
||||
mov ax, [disk_buffer+0x013]
|
||||
test ax, ax
|
||||
jnz .ret
|
||||
mov ax, [disk_buffer+0x020]
|
||||
mov dx, [disk_buffer+0x022]
|
||||
.ret: ret
|
||||
|
||||
; invoked after disk select
|
||||
load_bpb:
|
||||
; read word for "sectors per fat"
|
||||
mov ax, [disk_buffer+0x016]
|
||||
xor dx, dx
|
||||
; if zero, we need to check dword in BPB 7.1
|
||||
test ax, ax
|
||||
jnz .short_sf
|
||||
; fail if BPB 7.1 signature is not present
|
||||
mov cl, [disk_buffer+0x042]
|
||||
or cl, 1
|
||||
cmp cl, 0x29
|
||||
jne .err
|
||||
; load dword
|
||||
mov ax, [disk_buffer+0x024]
|
||||
mov dx, [disk_buffer+0x026]
|
||||
load_bpb: mov bx, [drive_ptr]
|
||||
; read word for "sectors per fat"
|
||||
mov ax, [diskbuf+0x016]
|
||||
xor dx, dx
|
||||
; if zero, we need to check dword in BPB 7.1
|
||||
test ax, ax
|
||||
jnz .short_sf
|
||||
; fail if BPB 7.1 signature is not present
|
||||
mov cl, [diskbuf+0x042]
|
||||
or cl, 1
|
||||
cmp cl, 0x29
|
||||
jne .err
|
||||
; load dword
|
||||
mov ax, [diskbuf+0x024]
|
||||
mov dx, [diskbuf+0x026]
|
||||
.short_sf:
|
||||
; store local value
|
||||
mov [fat_size], ax
|
||||
mov [fat_size+2], dx
|
||||
; store local value
|
||||
mov [bx+drive.fat_size], ax
|
||||
mov [bx+drive.fat_size+2], dx
|
||||
|
||||
; copy number of fat's
|
||||
xor ah, ah
|
||||
mov al, [disk_buffer+0x010]
|
||||
mov [fat_num], ax
|
||||
; copy number of fat's
|
||||
xor ah, ah
|
||||
mov al, [diskbuf+0x010]
|
||||
mov [bx+drive.fat_num], ax
|
||||
|
||||
; copy number of root directory entries
|
||||
mov ax, [disk_buffer+0x011]
|
||||
mov cl, 4
|
||||
shr ax, cl
|
||||
mov [rootdir_size], ax
|
||||
; copy number of root directory entries
|
||||
mov ax, [diskbuf+0x011]
|
||||
mov cl, 4
|
||||
shr ax, cl
|
||||
mov [bx+drive.dir_size], ax
|
||||
|
||||
; calculate offsets for everything
|
||||
mov ax, [part_offset]
|
||||
mov dx, [part_offset+2]
|
||||
; add reserved sectors
|
||||
add ax, [disk_buffer+0x0B+bpb_rsc]
|
||||
adc ax, 0
|
||||
; save begin of FAT tables
|
||||
mov [fat_offset], ax
|
||||
mov [fat_offset+2], dx
|
||||
; add FAT size * FAT number
|
||||
mov cx, [fat_num]
|
||||
.floop: add ax, [fat_size]
|
||||
adc dx, [fat_size+2]
|
||||
loop .floop
|
||||
; save begin of root directories
|
||||
mov [rootdir_offset], ax
|
||||
mov [rootdir_offset+2], dx
|
||||
; add root directory size (might be zero)
|
||||
add ax, [rootdir_size]
|
||||
adc dx, 0
|
||||
; save start of data area
|
||||
mov [clusters_offset], ax
|
||||
mov [clusters_offset+2], dx
|
||||
; calculate offsets for everything
|
||||
xor ax, ax
|
||||
xor dx, dx
|
||||
; add reserved sectors
|
||||
add ax, [diskbuf+0x0B+bpb_rsc]
|
||||
adc ax, 0
|
||||
; save begin of FAT tables
|
||||
mov [bx+drive.fat_offset], ax
|
||||
mov [bx+drive.fat_offset+2], dx
|
||||
; add FAT size * FAT number
|
||||
mov cx, [bx+drive.fat_num]
|
||||
.floop: add ax, [bx+drive.fat_size]
|
||||
adc dx, [bx+drive.fat_size+2]
|
||||
loop .floop
|
||||
; save begin of root directories
|
||||
mov [bx+drive.dir_offset], ax
|
||||
mov [bx+drive.dir_offset+2], dx
|
||||
; add root directory size (might be zero)
|
||||
add ax, [bx+drive.dir_size]
|
||||
adc dx, 0
|
||||
; save start of data area
|
||||
mov [bx+drive.clus_offset], ax
|
||||
mov [bx+drive.clus_offset+2], dx
|
||||
|
||||
call load_ts
|
||||
add ax, [part_offset]
|
||||
adc dx, [part_offset+2]
|
||||
sub ax, [clusters_offset]
|
||||
sbb dx, [clusters_offset+2]
|
||||
|
||||
; get "sectors per cluster"
|
||||
mov cl, [disk_buffer+0x00D]
|
||||
; this turns dx:ax from data sectors to number of clus
|
||||
.sloop: shr cl, 1
|
||||
test cl, cl
|
||||
jz .send
|
||||
clc
|
||||
rcr dx, 1
|
||||
rcr ax, 1
|
||||
jmp .sloop
|
||||
.send: mov [clusters_num], ax
|
||||
mov [clusters_num+2], dx
|
||||
|
||||
int 3
|
||||
|
||||
ret
|
||||
.err: stc
|
||||
ret
|
||||
ret
|
||||
.err: stc
|
||||
ret
|
||||
|
|
|
|||
Loading…
Reference in New Issue