CODEWITHSUNDEEP
assemblybootloaderbootable
int3
int3

Reputation: 658

Run C program after bootloader

I'm building a simple kernel for future tests applications, like MEMTEST and others.

So, what I have right now is the bootloader. What i need to do is load another file that I'll compile put in the second sector of the floppy disk and then run.

So, how can I load the rest of the floppy into RAM and then run?

You don't need to be 100% accurate, I just need to know and learn the necessary interrupts and "functions" to do that I need :)

just to share the bootloader:

[BITS 16] ;set 16bit mode
[ORG 0x7C00] ; address location where the program will run

jmp main ;start on main

main:
    mov si,hstr ; put the pointer into si register
    call printstr ;print hstr

    ;call load_kernel
    ;here we gonna load kernel into memory and then we will run it.

    mov si,mstr ; put the pointer into si register
    call printstr ;print mstr
    jmp hold ;idle the CPU


hold:
    hlt ;idle CPU

printstr:
    ;This will write in TTY char that will be loaded into al 8bit register.
    lodsb ;load into al
    cmp al,0 ; set flag if al is 0
    jnz print ; if isnt equal to 0 then jump to print
    ret ;else return to main
print: ;print the char
    mov ah,0x0E ;set the ah before calling the video interrupt
    int 10h ;here we go
    jmp printstr ;jump back
    ;

hstr db "Loading ...",13,10,0 ;define the strings. 13 is ASCII, 10 for new line, 0 is the null terminator
mstr db "CPU is now idle!",13,10,0

times 510 - ($-$$) db 0 ;fill the rest of the sector(less 2 last bytes) with 0's. 510-(here-start)=free space with 0's
dw 0xAA55               ;the last 2 bytes of the sector with AA55 signature. means that is the bootloader.

Upvotes: 4

Views: 1612

Answers (1)

Martin Rosenau
Martin Rosenau

Reputation: 18521

To load data from floppy disk or hard disk interrupt 13 (hexadecimal) is used.

Using the interrupt with floppy disk is more complicated (function AH=2 - that can also be used with hard disks - uses C/H/S-Addressing of sectors) than using hard disks (function AH=0x42 - which is not present in very old BIOSes (before the year 2000) - can only be used together with hard disks and not with floppy disks).

To run C code you need a C compiler generating 16-bit code (maybe the Watcom C compiler is still able to do this) or you have to switch to 32-bit protected mode.

The WIKI at "osdev.org" is a good resource for OS programming where you'll find a lot of information.

Upvotes: 2

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