Extended read

[bubach]

The cd-rom floppy emulation works like a partition on the cd-rom, which means that when you access it normally you would get 700-1.44 mb free space.
In DOS, this means:
A: would be the floppy "partition" at the cd-rom
D: would be the rest of the cd-rom

It exists other methods of making a bootable cd-rom (hdd emulation etc.), check out this page for more info:
http://utopia.knoware.nl/users/sanny/bootcd.html

If you read the PC Bootable CD-ROM from an already booted OS, such as DOS, Windows 95, Windows NT or OS/2 you'll only see the 'Data' that's on the Disc.
The Boot image (= floppy) is either:

• invisible
• displayed as BOOTCAT.BIN
• displayed as BOOTCAT.BIN and BOOTIMG.BIN

/ Christoffer

[ribas]

i was looking to BOS kernel and i don't understand this

The BOS 32-bit kernel, expects to be loaded at ;
; 1mb, a20 enabled.

use32
org 0x10000 ->??? why not 0x100000

[ribas]

here's what i?ve been trying to do ....

it needs mkisofs. Theorically it should work but i'm really a rookie is this ....

[FlashBurn]

I have a bootsector for cd-rom without emulating! It is not well documented, if you have any questions, ask! There should be enough place if you want to load your kernel at 1MiB! Also you need the newest FASM (beta) for assembling it!

Edit::

I forgot to upload the source code

[bubach]

Oh, I forgot to change that.. It should be: expects to be loaded at 64kb.

[ribas]

thanks FlashBurn great code !!

but now i'm stuck again ....
mov dl,byte[bootdrv] ;move bootdrive into dl for the loader

cli ; no interrupt
push ds

lgdt [gdtr] ; load gdt register

mov eax, cr0 ; switch to pmode by
inc ax ; toggling last bit
mov cr0, eax

mov bx, 0x08 ; select descriptor 1
mov ds, bx ; 8h = 1000b

dec ax ; switch back to real mode
mov cr0, eax ; by toggling bit again

pop ds ; get back old segment
sti



mov esi, 0x1000 ;
mov edi, 0x8000 ;
mov ecx, 0x4 ;
rep movsd


jmp 1000h:0000h ;where is loaded first (works fine!)

;how ho i jump to the other location ???? (the kernel is 16 bit code) just for testing
; jmp 8000h:0000h -> RIP > CS.limit

[ribas]

just forget it ...

a mov edx,edi
.....
call edx solved my problem ... i'm really new to this...

[FlashBurn]

You have to use this code:

Code: Select all

        mov ex,bx

        dec  ax      ; switch back to real mode
        mov  cr0, eax  ; by toggling bit again

        pop ds      ; get back old segment
        sti      

        mov esi,0x10000h
        mov edi,0x80000h
        mov ecx,4 ;are you sure this is enough (16bytes)?
        rep movsd

        jmp 8000h:0000h

[ribas]

It was just for testing ....

i'm still unable to load the kernel at 1 mb a jump to it from protected mode. I've used your code that load my kernel to 1000h:0000 and i'm limited to the 576kb of free space (i took these from bubach code) ... everything else is working fine as long as the kernel is in the imediate lba after the loader. I?m trying to build a generic program to work whith mkisofs in order to make bootable cd's in a really easy and configurable way (my aim is to be able to load any kernel that expects to be loaded at 1 mb) .. for now it just loads at 64kb ... the bootloader is responsable to check memory, video modes, a20, etc ... the kernel should load a new gdt. I started this because my laptop has no floppy drive .. and i was unable to test in the machine ... now i'm trying to make a more generic tool. thank you all

[FlashBurn]

If you want you also can have my code for a bootloader. This bootloader can load a kernel from a cd, from any directory - although I didn?t test it much - and it will load also kernels from fat12/16/32 disks like hdd, floppy, usb and zip!

[ribas]

if someone can post some code that moves 127 kb from 0x1000:0000 in unreal mode to 0x100000 and jumps to it in protected mode ..

jmp 0x08:?????? i can't get it to work ....

[ribas]

i just can make it work loading the kernel in real mode and moving it in pm mode to 1 mb ... so it stays size limited. i can't get the unreal mode move to work

[mystran]

Why not write a second-stage bootloader, which functions totally in protected mode, talking directly to whatever device your loading from? I mean, if you are going to write a protected-mode OS, you are going to need to know how to talk to hardware directly anyway, so you could just as well forget about BIOS in your bootloader too, and if you forget about BIOS, then there's no reason to use realmode at all.

[Brendan]

Hi,

i just can make it work loading the kernel in real mode and moving it in pm mode to 1 mb ... so it stays size limited. i can't get the unreal mode move to work

My floppy boot code is 1024 bytes (it loads it's second half before using it). The boot CD uses floppy emulation, so the code is the same. I use unreal mode to load a variable sized file (currently 480 Kb) to 0x00150000 - it should handle much larger files (depending on how much memory is installed).

The general idea is:

Code: Select all

main() {
   int bytes_left;

   load_second_boot_sector();
   enable_unreal_mode();
   load_first_sector_into_buffer();
   bytes_left = get_size_of_file_from_buffer();
   bytes_left -= size_of_sector;
   copy_buffer_to_final_address();
   while(bytes_left > 0) {
      load_next_sector_into_buffer();
      copy_buffer_to_final_address();
      bytes_left -= size_of_sector;
   }
   // Start the next stage here
}

See http://bcos.hopto.org/src/boot/boot144/index.html for my floppy boot code.


Cheers,

Brendan

[ribas]

FlashBurn can you send me the code that loads a file from any dir on a cd?