Boot loader/ru

Бут сектор загрузки для FDD. Рассмотрим код и опишем логику работы.

=======================================================

= boot program for Menuet OS version 1.00

= January 2002

=

= Copyright (C) Alex Nogueira Teixeira

= E-Mail

alexwal@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 $ 

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