328 lines
11 KiB
PHP
328 lines
11 KiB
PHP
; FAT-specific code for tmpdisk.asm.
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; Formats a disk to FAT16 or FAT32, depending on size.
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; Note: formatting is adjusted for memory-based disks. Although the resulting
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; image is a valid FAT32 volume, it has no "spare" sectors, e.g. second copy
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; of FAT or place for second sector of MS FAT32 bootloader.
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; Some constants
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FAT16_ROOTDIR_SECTORS = 16 ; can be changed, but why not?
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; FAT16:
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; 1 bootsector,
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; min 0xFF5 sectors for data,
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; min (0xFF5*2/512) = 16 sectors per FAT, we use only one copy,
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; FAT16_ROOTDIR_SECTORS for root directory
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MIN_FAT16_SIZE = 1 + 16 + FAT16_ROOTDIR_SECTORS + 0xFF5
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; FAT32:
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; 1 bootsector,
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; 1 sector for fsinfo,
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; min 0xFFF5 sectors for data,
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; min (0xFFF5*4/512) = 512 sectors per FAT, we use only one copy
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MIN_FAT32_SIZE = 1 + 1 + 512 + 0xFFF5
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MAX_SIZE = 1 shl (30 - 9) ; 1G in 512-byte sectors
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; Initializes FATxx structures on the disk.
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; Called with edi = pointer to disk data, esi = size of disk.
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proc format_disk
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; Determine FAT type and jump to the corresponding handler.
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cmp esi, MIN_FAT32_SIZE
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jae format_disk_fat32
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; Fall through to format_disk_fat16.
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endp
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; Structure of FAT16 bootsector. Field names are from MS spec.
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struc FAT16BOOT
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{
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.BS_jmpBoot rb 3
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.BS_OEMName rb 8
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.BPB_BytsPerSec dw ?
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.BPB_SecsPerClus db ?
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.BPB_RsvdSecCnt dw ?
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.BPB_NumFATs db ?
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.BPB_RootEntCnt dw ?
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.BPB_TotSec16 dw ?
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.BPB_Media db ?
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.BPB_FATSz16 dw ?
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.BPB_SecPerTrk dw ?
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.BPB_NumHeads dw ?
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.BPB_HiddSec dd ?
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.BPB_TotSec32 dd ?
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.BS_DrvNum db ?
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.BS_Reserved1 db ?
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.BS_BootSig db ?
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.BS_VolID dd ?
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.BS_VolLab rb 11
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.BS_FilSysType rb 8
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}
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virtual at 0
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FAT16BOOT FAT16BOOT
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end virtual
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; Initializes FAT16 structures on the disk.
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; Called with edi = pointer to disk data, esi = size of disk.
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format_disk_fat16:
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; 1. Calculate number of clusters.
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; 1a. There are fixed-sized areas and there are data+FAT;
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; every cluster uses 512 bytes in data area and 2 bytes in FAT area.
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lea eax, [esi-1-FAT16_ROOTDIR_SECTORS]
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; two following lines are equivalent to edx = floor(eax*512/514)
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mov ecx, 0xFF00FF01
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mul ecx ; edx = number of clusters
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; 1b. Force the number be less than 0xfff5.
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mov eax, 0xFFF4
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cmp edx, eax
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jb @f
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mov edx, eax
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@@:
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; 2. Zero all system areas on the disk.
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lea ecx, [256*(1+FAT16_ROOTDIR_SECTORS)/2+edx+255]
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and ecx, not 255
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shr ecx, 1
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xor eax, eax
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push edi
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rep stosd
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pop edi
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; 3. Generate the bootsector.
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; 3a. Copy static stub.
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push esi edi
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mov esi, fat16bootsector_stub
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mov ecx, fat16bootsector_stub_size
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rep movsb
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pop edi esi
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mov word [edi+510], 0xAA55
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; 3b. Set fields which depend on size.
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cmp esi, 0x10000
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jae .size_is_32bit
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mov [edi+FAT16BOOT.BPB_TotSec16], si
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jmp .size_written
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.size_is_32bit:
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mov [edi+FAT16BOOT.BPB_TotSec32], esi
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.size_written:
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lea eax, [edx+255]
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shr eax, 8
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mov [edi+FAT16BOOT.BPB_FATSz16], ax
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; 3c. Generate volume ID.
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call generate_volume_id
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mov [edi+FAT16BOOT.BS_VolID], eax
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; 4. Initialize FAT.
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mov dword [edi+512], 0xFFFFFFF8
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; 5. Return.
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ret
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; Structure of FAT32 bootsector. Field names are from MS spec.
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struc FAT32BOOT
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{
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.BS_jmpBoot rb 3
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.BS_OEMName rb 8
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.BPB_BytsPerSec dw ?
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.BPB_SecsPerClus db ?
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.BPB_RsvdSecCnt dw ?
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.BPB_NumFATs db ?
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.BPB_RootEntCnt dw ?
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.BPB_TotSec16 dw ?
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.BPB_Media db ?
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.BPB_FATSz16 dw ?
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.BPB_SecPerTrk dw ?
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.BPB_NumHeads dw ?
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.BPB_HiddSec dd ?
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.BPB_TotSec32 dd ?
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.BPB_FATSz32 dd ?
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.BPB_ExtFlags dw ?
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.BPB_FSVer dw ?
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.BPB_RootClus dd ?
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.BPB_FSInfo dw ?
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.BPB_BkBootSec dw ?
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.BPB_Reserved rb 12
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.BS_DrvNum db ?
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.BS_Reserved1 db ?
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.BS_BootSig db ?
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.BS_VolID dd ?
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.BS_VolLab rb 11
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.BS_FilSysType rb 8
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}
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virtual at 0
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FAT32BOOT FAT32BOOT
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end virtual
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; Initializes FAT32 structures on the disk.
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; Called with edi = pointer to disk data, esi = size of disk.
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format_disk_fat32:
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; 1. Calculate number of clusters.
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; 1a. There is fixed-sized area and there are data+FAT;
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; every cluster uses 512 bytes in data area and 4 bytes in FAT area.
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lea eax, [esi-1-1]
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; two following lines are equivalent to edx=floor(eax*512/516) if eax<10000000h
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mov ecx, 0xFE03F810
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mul ecx ; edx = number of clusters
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; 2. Zero all system areas on the disk and first cluster of data,
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; used for root directory.
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lea ecx, [128*(1+1+1)+edx+127]
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and ecx, not 127
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xor eax, eax
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push edi
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rep stosd
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pop edi
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; 3. Generate the bootsector.
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; 3a. Copy static stub.
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push esi edi
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mov esi, fat32bootsector_stub
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mov ecx, fat32bootsector_stub_size
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rep movsb
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pop edi esi
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mov word [edi+510], 0xAA55
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; 3b. Set fields which depend on size.
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mov [edi+FAT32BOOT.BPB_TotSec32], esi
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lea eax, [edx+127]
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shr eax, 7
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mov [edi+FAT32BOOT.BPB_FATSz32], eax
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; 3c. Generate volume ID.
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call generate_volume_id
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mov [edi+FAT32BOOT.BS_VolID], eax
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; 4. Initialize fsinfo sector.
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mov dword [edi+512], 'RRaA'
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mov dword [edi+512+484], 'rrAa'
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dec edx ; one cluster is occupied by root dir
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mov dword [edi+512+488], edx ; free count
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mov byte [edi+512+492], 3 ; first free cluster
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mov word [edi+512+510], 0xAA55
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; 5. Initialize FAT.
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mov dword [edi+512*2], 0x0FFFFFF8
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mov dword [edi+512*2+4], 0x0FFFFFFF
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mov dword [edi+512*2+8], 0x0FFFFFFF
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; 6. Return.
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ret
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; Generate volume serial number, which should try to be unique for each volume.
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; Use CMOS date+time, copy-pasted from fat32.inc.
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generate_volume_id:
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call get_time_for_file
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mov cx, ax
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call get_date_for_file
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shl eax, 16
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mov ax, cx
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ret
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; Three following procedures are copy-pasted from fat32.inc.
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bcd2bin:
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;----------------------------------
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; input : AL=BCD number (eg. 0x11)
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; output : AH=0
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; AL=decimal number (eg. 11)
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;----------------------------------
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xor ah, ah
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shl ax, 4
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shr al, 4
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aad
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ret
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get_date_for_file:
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;-----------------------------------------------------
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; Get date from CMOS and pack day,month,year in AX
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; DATE bits 0..4 : day of month 0..31
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; 5..8 : month of year 1..12
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; 9..15 : count of years from 1980
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;-----------------------------------------------------
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mov al, 0x7 ;day
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out 0x70, al
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in al, 0x71
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call bcd2bin
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ror eax, 5
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mov al, 0x8 ;month
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out 0x70, al
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in al, 0x71
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call bcd2bin
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ror eax, 4
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mov al, 0x9 ;year
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out 0x70, al
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in al, 0x71
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call bcd2bin
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add ax, 20 ;because CMOS return only the two last
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;digit (eg. 2000 -> 00 , 2001 -> 01) and we
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rol eax, 9 ;need the difference with 1980 (eg. 2001-1980)
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ret
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get_time_for_file:
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;-----------------------------------------------------
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; Get time from CMOS and pack hour,minute,second in AX
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; TIME bits 0..4 : second (the low bit is lost)
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; 5..10 : minute 0..59
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; 11..15 : hour 0..23
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;-----------------------------------------------------
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mov al, 0x0 ;second
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out 0x70, al
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in al, 0x71
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call bcd2bin
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ror eax, 6
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mov al, 0x2 ;minute
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out 0x70, al
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in al, 0x71
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call bcd2bin
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ror eax, 6
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mov al, 0x4 ;hour
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out 0x70, al
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in al, 0x71
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call bcd2bin
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rol eax, 11
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ret
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; some data
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fat16bootsector_stub:
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db 0EBh, 3Ch, 90h ; BS_jmpBoot
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db 'KOLIBRI ' ; BS_OEMName
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dw 512 ; BPB_BytsPerSec
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db 1 ; BPB_SecsPerClus
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dw 1 ; BPB_RsvdSecCnt
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db 1 ; BPB_NumFATs
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dw FAT16_ROOTDIR_SECTORS*16 ; BPB_RootEntCnt
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dw 0 ; BPB_TotSec16, filled in format_disk_fat16
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db 0F8h ; BPB_Media
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dw 0 ; BPB_FATSz16, filled in format_disk_fat16
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dw 32 ; BPB_SecPerTrk
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dw 128 ; BPB_NumHeads
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dd 0 ; BPB_HiddSec
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dd 0 ; BPB_TotSec32, filled in format_disk_fat16
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db 80h ; BS_DrvNum
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db 0 ; BS_Reserved1
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db 29h ; BS_BootSig
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dd 0 ; BS_VolID, filled in format_disk_fat16
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db 'NO NAME ' ; BS_VolLab
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db 'FAT16 ' ; BS_FilSysType
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; just in case add some meaningful bytes if someone tries to boot
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db 0CDh, 19h, 0EBh, 0FEh ; int 19h, jmp $
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fat16bootsector_stub_size = $ - fat16bootsector_stub
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fat32bootsector_stub:
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db 0EBh, 58h, 90h ; BS_jmpBoot
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db 'KOLIBRI ' ; BS_OEMName
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dw 512 ; BPB_BytsPerSec
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db 1 ; BPB_SecsPerClus
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dw 1 ; BPB_RsvdSecCnt
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db 1 ; BPB_NumFATs
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dw 0 ; BPB_RootEntCnt
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dw 0 ; BPB_TotSec16
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db 0F8h ; BPB_Media
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dw 0 ; BPB_FATSz16
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dw 32 ; BPB_SecPerTrk
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dw 128 ; BPB_NumHeads
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dd 0 ; BPB_HiddSec
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dd 0 ; BPB_TotSec32, filled in format_disk_fat32
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dd 0 ; BPB_FATSz32, filled in format_disk_fat32
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dw 0 ; BPB_ExtFlags
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dw 0 ; BPB_FSVer
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dd 2 ; BPB_RootClus
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dw 1 ; BPB_FSInfo
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dw 0 ; BPB_BkBootSec
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rb 12 ; BPB_Reserved
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db 80h ; BS_DrvNum
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db 0 ; BS_Reserved1
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db 29h ; BS_BootSig
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dd 0 ; BS_VolID, filled in format_disk_fat32
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db 'NO NAME ' ; BS_VolLab
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db 'FAT32 ' ; BS_FilSysType
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; same bytes as in fat16bootsector_stub
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db 0CDh, 19h, 0EBh, 0FEh ; int 19h, jmp $
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fat32bootsector_stub_size = $ - fat32bootsector_stub
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