failed to load file

[McZ]

I can't figure out what I'm doing wrong in my bootsector code, it failes to load the boot loader.. I'm trying to load it through the FAT12 filesystem but it failes to load it


source:
www.hig.se/~hco03phe/bootsctr.asm

[Curufir]

Your code to calculate the size of the root dir is wrong.

The calculation is:

Root_Dir_Size = ( (BPB_DirEntries * 32) / 512) rounded up

You're currently using:

Root_Dir_Size = ( ( (BPB_DirEntries * 32) + 512 - 1) / 512)

This is horribly wrong.

So use something like:

Code: Select all

MOV DX, [BPB_DirEntries]
AND DX, 0xF
JZ .1
ADD DX, 0x10
.1
SHR DX, 0x4

That error pretty much screws anything else you're trying to do.

[bakery2k]

The calculation is:

Root_Dir_Size = ( (BPB_DirEntries * 32) / 512) rounded up

You're currently using:

Root_Dir_Size = ( ( (BPB_DirEntries * 32) + 512 - 1) / 512)

This is horribly wrong.

Err...No. His calculation will produce the same result as yours.

[Curufir]

Yeah you're correct of course (Basic algebra coming back to haunt me ).

Hell, it'd be boring to be right all the time.

Waiter! More coffee.

[Curufir]

In penance I took another look.

This is one of the more amusing bugs I've seen.

Code: Select all

   div word[BPB_SectorsPerTrack]   ; divide AX with SectorsPerTrack (LBA / SPT)    inc dl                          ; increase the remainder of the division

There's no line break before the 'inc dl' instruction.

This means NASM interprets it as part of the comment and it's never assembled.

Which means all the LBAtoCHS conversions are wrong.

Nasty.

[McZ]

In penance I took another look.

This is one of the more amusing bugs I've seen.

Code: Select all

   div word[BPB_SectorsPerTrack]   ; divide AX with SectorsPerTrack (LBA / SPT)    inc dl                          ; increase the remainder of the division

There's no line break before the 'inc dl' instruction.

This means NASM interprets it as part of the comment and it's never assembled.

Which means all the LBAtoCHS conversions are wrong.

Nasty.

oh.. I can't remember there is missing a linebreak but I have to make sure as soon as I get home

but lets say there is a line break there is there anything else that can be wrong then?

[McZ]

so I have been trying to fix the problem with my file loader... but so far no success... altough I have found out that it looks like it doesn't load anything from disk, I used my bPrintHex16 function to print out the stuff in the FAT_BUFF and it writes only 0000 for each value.. wich wont be correct becouse I have one file that is 1kb in size, then it would be fitted into 2 sectors, but how come the 1 entry I should get in the FAT_BUFF is empty or 0000 ? shouldn't it be some other value?