Boot loader/ru
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Бут сектор загрузки для FDD. Рассмотрим код и опишем логику работы.
;== boot program for Kolibri OS version 1.00 ==
; January 2002
;
; Copyright (C) Alex Nogueira Teixeira
; E-Mail : alexwal{dog_}siteplanet.com.br
;
; Distributed under GPL, see file COPYING for details
;
; equates for program
;
; added support of config save
lf equ 0ah
cr equ 0dh
pos_read_tmp equ 0700h ;position for temporary read
boot_program equ 07c00h ;position for boot code
seg_read_kernel equ 01000h ;seguiment to kernel read
jmp start_program
nop
oemname db 'KOLIBRI '
bytespersector dw 512
sectorspercluster db 1
ressectors dw 1
numcopiesfat db 2
maxallocrootdir dw 224
maxsectors dw 2880 ;for 1.44 mbytes disk
mediadescriptor db 0f0h ;fd = 2 sides 18 sectors
sectorsperfat dw 9
sectorspertrack dw 18
heads dw 2
hiddensectors dd 0
hugesectors dd 0 ;if sectors > 65536
drivenumber db 0
db 0
bootsignature db 029h ;extended boot signature
volumeid dd 0
volumelabel db 'KOLIBRI '
filesystemtype db 'FAT12 '
start_program:
xor ax,ax
mov ss,ax
mov sp,boot_program
push ss
pop ds
mov si,loading+boot_program
loop_loading:
lodsb
or al,al
jz procura_arquivo_novamente
mov ah,0eh
mov bx,07h
int 010h
jmp loop_loading
procura_arquivo_novamente:
push ss
pop es
mov bp,16
newtry:
dec bp
jz mensagem_erro_arquivo
mov ax,020eh ;read, 14 sectors for directory
mov bx,pos_read_tmp ;es:bx read position
mov cx,02h ;track 0, sector 2
mov dx,0100h ;head 1, drive 0 (a:)
call read_sector
; int 013h ;read sectors
; jc newtry ; mensagem_erro_arquivo
mov si,bx
loop_compara_entrada_diretorio:
push si
mov cx,11 ;file name
mov di,arq_boot+boot_program
rep cmpsb
pop si
je le_arquivo_kernel
add si,32
cmp si,pos_read_tmp+(512*14) ;end of directory
jb loop_compara_entrada_diretorio
mensagem_erro_arquivo:
mov si,mens_erro+boot_program
loop_envio_mensagem:
lodsb
or al,al
jz espera_digitar_tecla
mov ah,0eh
mov bx,07h
int 010h
jmp loop_envio_mensagem
espera_digitar_tecla:
jmp $ ;зацикливание остановка пк.
;load kernel
le_arquivo_kernel:
mov bp,[si+01ah]
mov ax,0209h ;read, 9 sectors
mov bx,pos_read_tmp ;es:bx read position
mov cx,02h ;track 0, sector 2
xor dx,dx ;head 0, drive 0 (a:)
call read_sector
; int 013h ;read sectorsv
jc mensagem_erro_arquivo
mov ax,seg_read_kernel
mov es,ax
xor bx,bx
; \begin{diamond}[02.12.2005]
mov [cluster1st+boot_program], bp
; \end{diamond}[02.12.2005]
; read kernel to es:bx
loop_obtem_dados_kernel:
call le_setor_dados
jc mensagem_erro_arquivo
; add bx,0200h ;add one sector
push bx
mov bx,es
add bx,0x20
mov es,bx
pop bx
mov di,bp
shr di,01h
pushf
add di,bp
add di,pos_read_tmp
mov ax,[di]
popf
jc desloca_4_direita
and ax,0fffh
jmp verifica_fim_setores
desloca_4_direita:
mov cl,4
shr ax,cl
verifica_fim_setores:
cmp ax,0ff8h
jae executa_kernel
mov bp,ax
jmp loop_obtem_dados_kernel
executa_kernel:
; \begin{diamond}[02.12.2005]
mov ax, 'KL'
push 0
pop ds
mov si, loader_block+boot_program
; \end{diamond}[02.12.2005]
push word seg_read_kernel
push word 00h
retf
le_setor_dados: ;es:bx -> position in read buffer
;bp -> logical sector to read
;carry <- 0 read OK
;carry <- 1 read error
push bx
mov ax,0e2eh ;decimal point
xor bh,bh
int 010h
pop bx
mov ax,bp ;data sector to read
writesec:
add ax,31 ;get logical sector
mov cx,36 ;sector/track
xor dx,dx
div cx
mov ch,al ;track transfer
xor dh,dh ;head 0
cmp dl,18
jb cabeca_correta
sub dl,18
inc dh ;head 1
cabeca_correta:
inc dl
mov cl,dl
xor dl,dl ;drive 0 (a:)
patchhere:
mov ax,0201h ;read 1 sector
call read_sector
; int 013h
retn
read_sector:
push bp
mov bp,20
newread:
dec bp
jz mensagem_erro_arquivo
push ax bx cx dx
int 0x13
pop dx cx bx ax
jc newread
pop bp
retn
loading db 13,10,'Starting system ',00h
mens_erro:
db 13,10
arq_boot:
db 'KERNEL MNT ?',cr,lf,00h
errors db 16
; \begin{diamond}[02.12.2005]
write1st:
push cs
pop ds
mov byte [patchhere+2+boot_program], 3
mov ax, [cluster1st+boot_program]
push 1000h
pop es
xor bx, bx
call writesec
mov byte [patchhere+2+boot_program], 2
retf
cluster1st dw ?
loader_block:
db 1
dw 0
dw write1st+boot_program
dw 0
; \end{diamond}[02.12.2005]
times 0x1fe-$ db 00h
db 55h,0aah ;boot signature