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> OS Construction > convert nasm boot cde to fasm |
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mns 20 Apr 2009, 18:14
can some one tell me how to convert this nasm code(boot loder) to fasm? I tried to convert and could get bin file.but when I write it to flopy it didn't load fat12 system.
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20 Apr 2009, 18:14 |
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mns 20 Apr 2009, 18:46
I was doing my internship couldn't find lessure time.
(for 2nd why)sorry it's by mistake  |
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20 Apr 2009, 18:46 |
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LocoDelAssembly 20 Apr 2009, 18:49
Code: ;************************************************************************* ORG 0x7C00 jmp START OEM_ID db "QUASI-OS" BytesPerSector dw 0x0200 SectorsPerCluster db 0x01 ReservedSectors dw 0x0001 TotalFATs db 0x02 MaxRootEntries dw 0x00E0 TotalSectorsSmall dw 0x0B40 MediaDescriptor db 0xF0 SectorsPerFAT dw 0x0009 SectorsPerTrack dw 0x0012 NumHeads dw 0x0002 HiddenSectors dd 0x00000000 TotalSectorsLarge dd 0x00000000 DriveNumber db 0x00 Flags db 0x00 Signature db 0x29 VolumeID dd 0xFFFFFFFF VolumeLabel db "QUASI BOOT" SystemID db "FAT12" START: ; code located at 0000:7C00, adjust segment registers cli xor ax, ax mov ds, ax mov es, ax mov fs, ax mov gs, ax ; create stack mov ss, ax mov sp, 0x7C00 sti ; post message mov si, msgLoading call DisplayMessage LOAD_ROOT: ; compute size of root directory and store in "cx" xor cx, cx xor dx, dx mov ax, 0x0020 ; 32 byte directory entry mul WORD [MaxRootEntries] ; total size of directory div WORD [BytesPerSector] ; sectors used by directory xchg ax, cx ; compute location of root directory and store in "ax" mov al, BYTE [TotalFATs] ; number of FATs mul WORD [SectorsPerFAT] ; sectors used by FATs add ax, WORD [ReservedSectors] ; adjust for bootsector mov WORD [datasector], ax ; base of root directory add WORD [datasector], cx ; read root directory into memory (7C00:0200) mov bx, 0x0200 ; copy root dir above bootcode call ReadSectors ; browse root directory for binary image mov cx, WORD [MaxRootEntries] ; load loop counter mov di, 0x0200 ; locate first root entry .LOOP: push cx mov cx, 0x000B ; eleven character name mov si, ImageName ; image name to find push di rep cmpsb ; test for entry match pop di je LOAD_FAT pop cx add di, 0x0020 ; queuenext directory entry: loop .LOOP jmp FAILURE LOAD_FAT: ; save starting cluster of boot image mov si, msgCRLF call DisplayMessage mov dx, WORD [di + 0x001A] mov WORD [cluster], dx ; file's first cluster ; compute size of FAT and store in "cx" xor ax, ax mov al, BYTE [TotalFATs] ; number of FATs mul WORD [SectorsPerFAT] ; sectors used by FATs mov cx, ax ; compute location of FAT and store in "ax" mov ax, WORD [ReservedSectors] ; adjust for bootsector ; read FAT into memory (7C00:0200) mov bx, 0x0200 ; copy FAT above bootcode call ReadSectors ; read image file into memory (0050:0000) mov si, msgCRLF call DisplayMessage mov ax, 0x0050 mov es, ax ; destination for image mov bx, 0x0000 ; destination for image push bx LOAD_IMAGE: mov ax, WORD [cluster] ; cluster to read pop bx ; buffer to read into call ClusterLBA ; convert cluster to LBA xor cx, cx mov cl, BYTE [SectorsPerCluster] ; sectors to read call ReadSectors push bx ; compute next cluster mov ax, WORD [cluster] ; identify current cluster mov cx, ax ; copy current cluster mov dx, ax ; copy current cluster shr dx, 0x0001 ; divide by two add cx, dx ; sum for (3/2) mov bx, 0x0200 ; location of FAT in memory add bx, cx ; index into FAT mov dx, WORD [bx] ; read two bytes from FAT test ax, 0x0001 jnz .ODD_CLUSTER .EVEN_CLUSTER: and dx, 0000111111111111b ; take low twelve bits jmp .DONE .ODD_CLUSTER: shr dx, 0x0004 ; take high twelve bits .DONE: mov WORD [cluster], dx ; store new cluster cmp dx, 0x0FF0 ; test for end of file jb LOAD_IMAGE DONE: mov si, msgCRLF call DisplayMessage push WORD 0x0050 push WORD 0x0000 retf FAILURE: mov si, msgFailure call DisplayMessage mov ah, 0x00 int 0x16 ; await keypress int 0x19 ; warm boot computer ;************************************************************************* ; PROCEDURE DisplayMessage ; display ASCIIZ string at "ds:si" via BIOS ;************************************************************************* DisplayMessage: lodsb ; load next character or al, al ; test for NUL character jz .DONE mov ah, 0x0E ; BIOS teletype mov bh, 0x00 ; display page 0 mov bl, 0x07 ; text attribute int 0x10 ; invoke BIOS jmp DisplayMessage .DONE: ret ;************************************************************************* ; PROCEDURE ReadSectors ; reads "cx" sectors from disk starting at "ax" into memory location "es:bx" ;************************************************************************* ReadSectors: .MAIN: mov di, 0x0005 ; five retries for error .SECTORLOOP: push ax push bx push cx call LBACHS mov ah, 0x02 ; BIOS read sector mov al, 0x01 ; read one sector mov ch, BYTE [absoluteTrack] ; track mov cl, BYTE [absoluteSector] ; sector mov dh, BYTE [absoluteHead] ; head mov dl, BYTE [DriveNumber] ; drive int 0x13 ; invoke BIOS jnc .SUCCESS ; test for read error xor ax, ax ; BIOS reset disk int 0x13 ; invoke BIOS dec di ; decrement error counter pop cx pop bx pop ax jnz .SECTORLOOP ; attempt to read again int 0x18 .SUCCESS: mov si, msgProgress call DisplayMessage pop cx pop bx pop ax add bx, WORD [BytesPerSector] ; queue next buffer inc ax ; queue next sector loop .MAIN ; read next sector ret ;************************************************************************* ; PROCEDURE ClusterLBA ; convert FAT cluster into LBA addressing scheme ; LBA = (cluster - 2) * sectors per cluster ;************************************************************************* ClusterLBA: sub ax, 0x0002 ; zero base cluster number xor cx, cx mov cl, BYTE [SectorsPerCluster] ; convert byte to word mul cx add ax, WORD [datasector] ; base data sector ret ;************************************************************************* ; PROCEDURE LBACHS ; convert "ax2; LBA addressing scheme to CHS addressing scheme ; absolute sector = (logical sector / sectors per track) + 1 ; absolute head = (logical sector / sectors per track) MOD number of heads ; absolute track = logical sector / (sectors per track * number of heads) ;************************************************************************* LBACHS: xor dx, dx ; prepare dx:ax for operation div WORD [SectorsPerTrack] ; calculate inc dl ; adjust for sector 0 mov BYTE [absoluteSector], dl xor dx, dx ; prepare dx:ax for operation div WORD [NumHeads] ; calculate mov BYTE [absoluteHead], dl mov BYTE [absoluteTrack], al ret absoluteSector db 0x00 absoluteHead db 0x00 absoluteTrack db 0x00 datasector dw 0x0000 cluster dw 0x0000 ImageName db "LOADER BIN" msgLoading db 0x0D, 0x0A, "Loading Boot Image ", 0x0D, 0x0A, 0x00 msgCRLF db 0x0D, 0x0A, 0x00 msgProgress db ".", 0x00 msgFailure db 0x0D, 0x0A, "ERROR : Press Any Key to Reboot", 0x00 ; Padding before boot signature rb 512 - 2 + $$ - $ dw $AA55 ;************************************************************************* BTW, are you sure nasm version was working? The modifications I did will hardly solve the problem you comment. I tried replacing the first sector of a formatted floppy image with the binary and also had the problem of unrecognizable format (Windows asked me if I want to format the disk). |
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20 Apr 2009, 18:49 |
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mns 20 Apr 2009, 18:59
yes nasm one worked well
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20 Apr 2009, 18:59 |
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Coddy41 20 Apr 2009, 19:12
locodelassembly wrote:
that's sorta messed up :/ |
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20 Apr 2009, 19:12 |
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LocoDelAssembly 20 Apr 2009, 19:16
But is it really at the original state? For example, I had to correct some labels that started with dot but missed the double-dot at the end, nasm really compiles that?
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20 Apr 2009, 19:16 |
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Coddy41 20 Apr 2009, 19:22
I geuss http://www.csee.umbc.edu/help/nasm/sample.shtml But not all the time
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20 Apr 2009, 19:22 |
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LocoDelAssembly 20 Apr 2009, 19:34
Coddy41, but I don't see there a line with only ".aLabel" but ".aLabel db ..." which of course ":" is not needed there. The labels I was referring to were those you jump to (like ".SUCCESS:" that was ".SUCCESS").
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20 Apr 2009, 19:34 |
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mns 21 Apr 2009, 13:34
sorry for the delay I'm attaching the BIN file(in rar file) I've got after compiling the code with nasm.it is working very well when it copied to 1st boot sector of a floppy
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21 Apr 2009, 13:34 |
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LocoDelAssembly 21 Apr 2009, 15:50
AAAAHH!!! Now I know what was happening. Add a NOP after the "jmp START" instruction or change it to "jmp near START".
BTW, sorry for still asking but did the original nasm source included "jmp START" or perhaps it had some specifier (like "near" for fasm) to make it 3 bytes long? I find strange that nasm didn't optimized the instruction to use the shortest encoding  |
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21 Apr 2009, 15:50 |
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mns 21 Apr 2009, 17:21
yes, in original nasm source there is "jmp START"and no specifier.(I'm reattaching the original source)
And your solution working just fine  .
many many thanks
by the way, these are 2 sites to a beginner to os development(like me )and from where I'v got that source
www.mohanraj.info/josh.jsp www.geocities.com/mvea/bootstrap.htm
Last edited by mns on 22 Apr 2009, 15:31; edited 3 times in total |
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21 Apr 2009, 17:21 |
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Coddy41 21 Apr 2009, 18:47
I found this great when I wanted to start OS coding, uses asm, C, and fasm I think
 maybe some nasm here and there. http://www.osdever.net/tutorials.php?cat=0 |
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21 Apr 2009, 18:47 |
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mns 22 Apr 2009, 15:20
thanks!
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22 Apr 2009, 15:20 |
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