| 21,8 → 21,6 |
|---|
| ; Boot Sector and BPB Structure |
| include 'floppy1440.inc' |
| ;include 'floppy2880.inc' |
| ;include 'floppy1680.inc' |
| ;include 'floppy1743.inc' |
| |
| start_program: |
| |
| 47,30 → 45,8 |
|---|
| push ss |
| pop es |
| |
| ; calculate some disk parameters |
| ; - beginning sector of RootDir |
| mov ax,word [BPB_FATSz16+boot_program] |
| xor cx,cx |
| mov cl,byte [BPB_NumFATs+boot_program] |
| mul cx |
| add ax,word [BPB_RsvdSecCnt+boot_program] |
| mov word [FirstRootDirSecNum+boot_program],ax ; 19 |
| mov si,ax |
| |
| ; - count of sectors in RootDir |
| mov bx,word [BPB_BytsPerSec+boot_program] |
| mov cl,5 ; divide ax by 32 |
| shr bx,cl ; bx = directory entries per sector |
| mov ax,word [BPB_RootEntCnt+boot_program] |
| xor dx,dx |
| div bx |
| mov word [RootDirSecs+boot_program],ax ; 14 |
| |
| ; - data start |
| add si,ax ; add beginning sector of RootDir and count sectors in RootDir |
| mov word [data_start+boot_program],si ; 33 |
| ; reading root directory |
| ; al=count root dir sectrors !!!! TODO: al, max 255 sectors !!!! |
| ; al=count root dir sectors !!!! TODO: al, max 255 sectors !!!! |
| mov ah,2 ; read |
| push ax |
| |
| 96,22 → 72,8 |
|---|
| add si,32 ; next dir. entry |
| cmp si,ax ; end of directory |
| jb loop_find_dir_entry |
| jmp $ |
| |
| file_error_message: |
| mov si,error_message+boot_program |
| |
| loop_error_message: |
| lodsb |
| or al,al |
| jz freeze_pc |
| mov ah,0eh |
| mov bx,7 |
| int 10h |
| jmp loop_error_message |
| |
| freeze_pc: |
| jmp $ ; endless loop |
| |
| ; === KERNEL FOUND. LOADING... === |
| |
| found_kernel_file: |
| 127,29 → 89,18 |
|---|
| mov ah,2 ; ah=2 (read) |
| mov al, byte [BPB_FATSz16+boot_program] ; FAT size in sectors (TODO: max 255 sectors) |
| call read_sector |
| jc file_error_message ; read error |
| |
| mov ax,seg_read_kernel |
| mov es,ax |
| xor bx,bx ; es:bx = 1000h:0000h |
| |
| |
| ; reading kernel file |
| loop_obtains_kernel_data: |
| ; read one cluster of file |
| call obtain_cluster |
| jc file_error_message ; read error |
| call obtain_cluster ; read one cluster of file |
| |
| ; add one cluster length to segment:offset |
| push bx |
| mov bx,es |
| mov ax,word [BPB_BytsPerSec+boot_program] ;\ |
| movsx cx,byte [BPB_SecPerClus+boot_program] ; | !!! TODO: !!! |
| mul cx ; | out this from loop !!! |
| shr ax,4 ;/ |
| add bx,ax |
| mov es,bx |
| pop bx |
| mov ax,es |
| add ax,seg_inc_per_cluster ; << =32(1.44M) or 64(2.88) >> |
| mov es,ax ; add one cluster length to segment:offset |
| |
| mov di,bp |
| shr di,1 |
| 162,8 → 113,7 |
|---|
| and ax,0fffh |
| jmp verify_end_sector |
| move_4_right: |
| mov cl,4 |
| shr ax,cl |
| shr ax,4 |
| verify_end_sector: |
| cmp ax,0ff8h ; last cluster |
| jae execute_kernel |
| 194,73 → 144,55 |
|---|
| mov ax,0e2eh ; ah=0eh (teletype), al='.' |
| xor bh,bh |
| int 10h |
| ; jc $ ; error |
| pop bx |
| |
| writesec: |
| ; convert cluster number to sector number |
| mov ax,bp ; data cluster to read |
| sub ax,2 |
| xor bx,bx |
| mov bl,byte [BPB_SecPerClus+boot_program] |
| mul bx |
| ;>> add ax,ax ; << only for 2.88M disks! >> |
| add ax,word [data_start+boot_program] |
| pop bx |
| call conv_abs_to_THS ; convert abs sector (AX) to BIOS T:H:S (track:head:sector) |
| |
| writesec: |
| call conv_abs_to_THS ; convert abs sector (AX) to BIOS T:H:S (track:head:sector) |
| patchhere: |
| mov ah,2 ; ah=2 (read) |
| mov al,byte [BPB_SecPerClus+boot_program] ; al=(one cluster) |
| call read_sector |
| retn |
| ;------------------------------------------ |
| mov ax,0x201 ; ah=2 (read) |
| ;>> ; al=1(1.44) or 2(2.88) |
| ; read sector from disk |
| |
| ;------------------------------------------ |
| ; read sector from disk |
| read_sector: |
| push bp |
| mov bp,20 ; try 20 times |
| newread: |
| dec bp |
| jz file_error_message |
| push ax bx cx dx |
| int 13h |
| jc $ ; error: stop here |
| pop dx cx bx ax |
| jc newread |
| pop bp |
| retn |
| |
| ;------------------------------------------ |
| ; convert abs. sector number (AX) to BIOS T:H:S |
| ; sector number = (abs.sector%BPB_SecPerTrk)+1 |
| ; pre.track number = (abs.sector/BPB_SecPerTrk) |
| ; head number = pre.track number%BPB_NumHeads |
| ; track number = pre.track number/BPB_NumHeads |
| ; Return: cl - sector number |
| ; ch - track number |
| ; converts abs. sector number (AX) to BIOS T:H:S |
| ; Returns: {pre.track number = (AX / BPB_SecPerTrk)} |
| ; ch - track number = pre.track number/2 |
| ; cl - sector number = (abs.sector%BPB_SecPerTrk)+1 |
| ; dh - head number = pre.track number%BPB_NumHeads |
| ; dl - drive number (0 = a:) |
| ; dh - head number |
| conv_abs_to_THS: |
| push bx |
| mov bx,word [BPB_SecPerTrk+boot_program] |
| mov cx,word [BPB_SecPerTrk+boot_program] ; << 18 or 36 >> |
| xor dx,dx |
| div bx |
| div cx |
| inc dx |
| mov cl, dl ; cl = sector number |
| mov bx,word [BPB_NumHeads+boot_program] |
| xor dx,dx |
| div bx |
| ; !!!!!!! ax = track number, dx = head number |
| shr ax, 1 |
| rol dx, 1 ; dh = head number |
| mov ch,al ; ch=track number |
| xchg dh,dl ; dh=head number |
| mov dl,0 ; dl=0 (drive 0 (a:)) |
| pop bx |
| retn |
| ;------------------------------------------ |
| |
| loading db cr,lf,'Starting system ',00h |
| error_message db 13,10 |
| kernel_name db 'KERNEL MNT ?',cr,lf,00h |
| FirstRootDirSecNum dw ? |
| RootDirSecs dw ? |
| data_start dw ? |
| ;error_message db 13,10 |
| kernel_name db 'KERNEL MNT',00h |
| FirstRootDirSecNum dw 19 ; 1st sector of the root dir |
| RootDirSecs dw 14 ; << = 14(1.44M) or 15(2.88M) >> |
| data_start dw 33 ; << = 33(1.44M) or 34(2.88M) >> |
| |
| ; <diamond> |
| write1st: |
| 267,7 → 199,7 |
|---|
| push cs |
| pop ds |
| mov byte [patchhere+1+boot_program], 3 ; change ah=2 to ah=3 |
| mov ax,[cluster1st+boot_program] |
| mov bp,[cluster1st+boot_program] |
| push 1000h |
| pop es |
| xor bx,bx |
| 274,7 → 206,8 |
|---|
| call writesec |
| mov byte [patchhere+1+boot_program], 2 ; change back ah=3 to ah=2 |
| retf |
| cluster1st dw ? |
| |
| cluster1st dw ? ; 1st cluster of kernel.mnt |
| loader_block: |
| db 1 |
| dw 0 |