Programming Forums > Application Development > Assembly

grimpirate · Oct 20th, 2006, 6:12 PM

The menuetOS code doesn't set those up, all the Bochs emulator has is its own emulated BIOS code of which apparently one of them is the interrupt vector 10h. The menuetOS isn't an OS that I'm loading on the system. I'm EXCLUSIVELY using the menuetOS code that is listed here (the TOTAL code actually loaded the OS, I just stripped it down to display a string) and from what I can tell in the code it's not redefining any interrupts and it also makes use of 10h. The major difference is that the menuetOS code segment works. I cannot say more about the emulated BIOS that Bochs is currently using because I don't know enough about it. All I know is that these two code segments when executed individually under the same procedure and environment. One works and one doesn't. Therefore, the answer lies somewhere in the code that I have posted here. I'm hoping that someone can point out what that key difference is.

grimpirate · Oct 20th, 2006, 6:53 PM

Never mind I believe I've discovered the problem and it was in my own code, apparently I need to make a series of declarations regarding the sectors per cluster and other such things immediately after the jmp and nop since apparently these are required by BIOS or DOS or something or other. To see what I mean look here http://www.exegesis.uklinux.net/gand...t/disk.htm#7.3 that information is included in the MenuetOS code which works (I neglected to post it here thinking it was superfluous data).

niteice · Oct 20th, 2006, 8:47 PM

That's only if you're interested in writing anything to do with FAT-formatted disks.

grimpirate · Oct 20th, 2006, 9:43 PM

Yes the majority of that deals with writing to a FAT filesystem. However, it shows the general structure of the boot sector before any file operations. The code for the menuetOS that I posted previously for instance, won't load. However this code:

(Toggle Plain Text)

boot_program	   equ 07c00h ;position for boot code
   
		   jmp start_program
		   nop
   
oemname 	   db 'MENUETOS'
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 'MENUET DISK'
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

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 $

loading   db 13,10,'Starting MenuetOS ',00h


times 0x1fe-$ db 00h

  db 55h,0aah ;boot signature

With the relevant declarations of bytes and words at the beginning does launch successfully. So I'm figuring that snippet of code is what makes all the difference. As the author of the link that I stated he shows that the boot sector can be divided into 6 areas:
Assembly Language Jump to Boot Code
Disk Parameters Needed by DOS
Assembly Language Boot Code
Error Messages
System File Names
DOS Signature
The DOS Signature refers to the 'magic number' 55aah, the Assembly Language Jump to Boot Code is a DOS requirement according to the author along with a NOP after it, precisely as the menuetOS author is doing. The Disk Paramters Needed by DOS are those that the menuetOS author has included on his code, finally the actual boot strapper code is located in Assembly Language Boot Code, the Error Messages and System File Names are also part of that if I'm not mistaken but are this FAT system specific code of the author.

grimpirate · Oct 20th, 2006, 11:17 PM

Ya my idea doesn't seem to work either. Man this is discouraging, Polyphemus was SO right lol. Don't I have access to the BIOS interrupts once the BIOS transfers control to my boot loader?

niteice · Oct 20th, 2006, 11:32 PM

Yes.

I don't see why you would need to declare the FAT header if you're not doing any FAT operations yet.

grimpirate · Oct 21st, 2006, 12:13 AM

I don't know why either, but apparently Bochs requires it 'cause I just got some workng code! :banana:

(Toggle Plain Text)

jmp boot_code
nop

SystemID                db      'ComandOS'
BytesPerSector          dw      512
SectorsPerCluster       db      1
ReservedSector          dw      1
NumOfFATS               db      2
RootDirEntries          dw      224
SectorsOnDisk           dw      2880
FormatID                db      0f0h
SectorsPerFat           dw      9
SectorsPerTrack         dw      18
NumOfHeads              dw      2
HiddenSectors           dd      0
BigSectors              dd      0
DriveNumber             db      0
Reserved                db      0
ExtendedBootSig         db      029h
VolumeSerialNum         dd      0
VolumeLabel             db      'COS DISK   '
FileSystemType          db      'FAT12   '

boot_code:
mov ah, 0eh
mov al, 97
int 10h
@@:
nop
jmp @b

times 0x1fe-$ db 00h
db 55h,0aah

It prints the character 'a' :banana:

faital · Nov 14th, 2006, 7:32 AM

Hi, This post is very informative, however I would like some specific information. If someone can help me then please send me a private message. Best Regards,

Harakim · Dec 5th, 2006, 8:13 PM

When you use 'int 10h', you are telling your BIOS that you want to change the display mode to whatever mode is in register ah.
It is possible your hardware's graphic mode 9 is not the same as it is in Boch's. In this case you may be displaying pixels rather than text or something like that and the pixel may be too dim or small to see. Make sure you are using the right modes with your 10h interrupt. (I do know it works now, though.)

Just a thought.

P.S. Remember, usually in text mode one memory location is the character and right next to it are the color settings. Putting a string into memory on your gfx card won't usually work.

lectricpharaoh · Dec 5th, 2006, 10:01 PM

Quote:

Originally Posted by Harakim

When you use 'int 10h', you are telling your BIOS that you want to change the display mode to whatever mode is in register ah.
It is possible your hardware's graphic mode 9 is not the same as it is in Boch's. In this case you may be displaying pixels rather than text or something like that and the pixel may be too dim or small to see. Make sure you are using the right modes with your 10h interrupt. (I do know it works now, though.)

Just a thought.

P.S. Remember, usually in text mode one memory location is the character and right next to it are the color settings. Putting a string into memory on your gfx card won't usually work.

Two things: INT 10H in the BIOS on most (IBM-compatible) PCs is actually a whole mess of functions, not just mode set. It depends on the register values you pass, though I can't recall which is which (been a long time since I've perused Ralf's list). Second: You certainly can put a string into the memory of your graphics card, at least with most display adapters. The 'text mode' that most are in at system startup is a block of memory with one 16-bit word per character. One byte of each word is the attribute (bit flags for color, basically), and the other is the character itself.

Oct 20th, 2006, 6:12 PM	#11
grimpirate King of Portal Join Date: Sep 2005 Posts: 439 Rep Power: 4	The menuetOS code doesn't set those up, all the Bochs emulator has is its own emulated BIOS code of which apparently one of them is the interrupt vector 10h. The menuetOS isn't an OS that I'm loading on the system. I'm EXCLUSIVELY using the menuetOS code that is listed here (the TOTAL code actually loaded the OS, I just stripped it down to display a string) and from what I can tell in the code it's not redefining any interrupts and it also makes use of 10h. The major difference is that the menuetOS code segment works. I cannot say more about the emulated BIOS that Bochs is currently using because I don't know enough about it. All I know is that these two code segments when executed individually under the same procedure and environment. One works and one doesn't. Therefore, the answer lies somewhere in the code that I have posted here. I'm hoping that someone can point out what that key difference is. __________________ Lo, there do I see my father. 'Lo, there do I see My mother, and my sisters, and my brothers. 'Lo, there do I see The line of my people... Back to the beginning. 'Lo, they do call to me. They bid me take my place among them. In the halls of Valhalla... Where the brave... May live... ...forever.. GrimBB \| Mimesis

Oct 20th, 2006, 6:53 PM	#12
grimpirate King of Portal Join Date: Sep 2005 Posts: 439 Rep Power: 4	Never mind I believe I've discovered the problem and it was in my own code, apparently I need to make a series of declarations regarding the sectors per cluster and other such things immediately after the jmp and nop since apparently these are required by BIOS or DOS or something or other. To see what I mean look here http://www.exegesis.uklinux.net/gand...t/disk.htm#7.3 that information is included in the MenuetOS code which works (I neglected to post it here thinking it was superfluous data). __________________ Lo, there do I see my father. 'Lo, there do I see My mother, and my sisters, and my brothers. 'Lo, there do I see The line of my people... Back to the beginning. 'Lo, they do call to me. They bid me take my place among them. In the halls of Valhalla... Where the brave... May live... ...forever.. GrimBB \| Mimesis

Oct 20th, 2006, 9:43 PM	#14
grimpirate King of Portal Join Date: Sep 2005 Posts: 439 Rep Power: 4	Yes the majority of that deals with writing to a FAT filesystem. However, it shows the general structure of the boot sector before any file operations. The code for the menuetOS that I posted previously for instance, won't load. However this code: (Toggle Plain Text) boot_program equ 07c00h ;position for boot code jmp start_program nop oemname db 'MENUETOS' 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 'MENUET DISK' 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 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 $ loading db 13,10,'Starting MenuetOS ',00h times 0x1fe-$ db 00h db 55h,0aah ;boot signature boot_program equ 07c00h ;position for boot code jmp start_program nop oemname db 'MENUETOS' 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 'MENUET DISK' 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 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 $ loading db 13,10,'Starting MenuetOS ',00h times 0x1fe-$ db 00h db 55h,0aah ;boot signature With the relevant declarations of bytes and words at the beginning does launch successfully. So I'm figuring that snippet of code is what makes all the difference. As the author of the link that I stated he shows that the boot sector can be divided into 6 areas: Assembly Language Jump to Boot Code Disk Parameters Needed by DOS Assembly Language Boot Code Error Messages System File Names DOS Signature The DOS Signature refers to the 'magic number' 55aah, the Assembly Language Jump to Boot Code is a DOS requirement according to the author along with a NOP after it, precisely as the menuetOS author is doing. The Disk Paramters Needed by DOS are those that the menuetOS author has included on his code, finally the actual boot strapper code is located in Assembly Language Boot Code, the Error Messages and System File Names are also part of that if I'm not mistaken but are this FAT system specific code of the author. __________________ Lo, there do I see my father. 'Lo, there do I see My mother, and my sisters, and my brothers. 'Lo, there do I see The line of my people... Back to the beginning. 'Lo, they do call to me. They bid me take my place among them. In the halls of Valhalla... Where the brave... May live... ...forever.. GrimBB \| Mimesis

Oct 20th, 2006, 11:17 PM	#15
grimpirate King of Portal Join Date: Sep 2005 Posts: 439 Rep Power: 4	Ya my idea doesn't seem to work either. Man this is discouraging, Polyphemus was SO right lol. Don't I have access to the BIOS interrupts once the BIOS transfers control to my boot loader? __________________ Lo, there do I see my father. 'Lo, there do I see My mother, and my sisters, and my brothers. 'Lo, there do I see The line of my people... Back to the beginning. 'Lo, they do call to me. They bid me take my place among them. In the halls of Valhalla... Where the brave... May live... ...forever.. GrimBB \| Mimesis

Oct 21st, 2006, 12:13 AM	#17
grimpirate King of Portal Join Date: Sep 2005 Posts: 439 Rep Power: 4	I don't know why either, but apparently Bochs requires it 'cause I just got some workng code! :banana: (Toggle Plain Text) jmp boot_code nop SystemID db 'ComandOS' BytesPerSector dw 512 SectorsPerCluster db 1 ReservedSector dw 1 NumOfFATS db 2 RootDirEntries dw 224 SectorsOnDisk dw 2880 FormatID db 0f0h SectorsPerFat dw 9 SectorsPerTrack dw 18 NumOfHeads dw 2 HiddenSectors dd 0 BigSectors dd 0 DriveNumber db 0 Reserved db 0 ExtendedBootSig db 029h VolumeSerialNum dd 0 VolumeLabel db 'COS DISK ' FileSystemType db 'FAT12 ' boot_code: mov ah, 0eh mov al, 97 int 10h @@: nop jmp @b times 0x1fe-$ db 00h db 55h,0aah jmp boot_code nop SystemID db 'ComandOS' BytesPerSector dw 512 SectorsPerCluster db 1 ReservedSector dw 1 NumOfFATS db 2 RootDirEntries dw 224 SectorsOnDisk dw 2880 FormatID db 0f0h SectorsPerFat dw 9 SectorsPerTrack dw 18 NumOfHeads dw 2 HiddenSectors dd 0 BigSectors dd 0 DriveNumber db 0 Reserved db 0 ExtendedBootSig db 029h VolumeSerialNum dd 0 VolumeLabel db 'COS DISK ' FileSystemType db 'FAT12 ' boot_code: mov ah, 0eh mov al, 97 int 10h @@: nop jmp @b times 0x1fe-$ db 00h db 55h,0aah It prints the character 'a' :banana: __________________ Lo, there do I see my father. 'Lo, there do I see My mother, and my sisters, and my brothers. 'Lo, there do I see The line of my people... Back to the beginning. 'Lo, they do call to me. They bid me take my place among them. In the halls of Valhalla... Where the brave... May live... ...forever.. GrimBB \| Mimesis

Oct 20th, 2006, 8:47 PM	#13
niteice Programmer Join Date: Aug 2005 Posts: 98 Rep Power: 4	That's only if you're interested in writing anything to do with FAT-formatted disks.

Oct 20th, 2006, 11:32 PM	#16
niteice Programmer Join Date: Aug 2005 Posts: 98 Rep Power: 4	Yes. I don't see why you would need to declare the FAT header if you're not doing any FAT operations yet.

Nov 14th, 2006, 7:32 AM	#18
faital Newbie Join Date: Nov 2006 Posts: 1 Rep Power: 0	Hi, This post is very informative, however I would like some specific information. If someone can help me then please send me a private message. Best Regards, __________________ Buy Property \| Dropshipping Directory Canada Wholesale \| UK Wholesale Directory

Dec 5th, 2006, 8:13 PM	#19
Harakim Hobbyist Programmer Join Date: May 2006 Location: West Jordan, Utah, United States Posts: 176 Rep Power: 3	When you use 'int 10h', you are telling your BIOS that you want to change the display mode to whatever mode is in register ah. It is possible your hardware's graphic mode 9 is not the same as it is in Boch's. In this case you may be displaying pixels rather than text or something like that and the pixel may be too dim or small to see. Make sure you are using the right modes with your 10h interrupt. (I do know it works now, though.) Just a thought. P.S. Remember, usually in text mode one memory location is the character and right next to it are the color settings. Putting a string into memory on your gfx card won't usually work.

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Programming Forums > Application Development > Assembly

Why doesn't this work?