Hello,
I'm making my bootloader and I want to use some filesystem to load my kernel. I chosen FAT12(because I think that's one of the best ways, if I'm wrong, correct me:)). What ways and what things do I have to do, to load a file from Real Mode?
16Bit FAT12
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bluecode
Re:16Bit FAT12
hi,
I would consider writing your own bootloader a bad choice, because there are just thousands of them on the net and imho it doesn't help you learning assembler. It's just plain&simple frustrating.
But back to your question
Quoting from here:
1. The DOS Boot Record (DBR) is read to determine the size of the DBR, FAT, and Root Directory. The location of each on the disk is then determined.
2. The Root Directory is read in to memory.
3. The Root Directory is searched for the file name LOADER.BIN. If found, we can look in the directory entry to find out which is the file?s first cluster (file allocation unit). If not found, we give an error message.
4. The File Allocation Table is read off the disk in to memory.
5. Starting with the file?s first cluster, we use the FAT to locate all the clusters belonging to the file. We read them all off the disk into memory at a specific location.
6. We jump to that location to begin execution of the operating system.
I also think that fat is a bad choice, because it's limitations (8 letter names + 3 extension, only capital letters, ...). On the other hand it's one of the simplest filesystems on earth and it's supported by microsoft and it's specification is freely available. I plan to use ext2/3 or reiserfs as root filesystem.
I would consider writing your own bootloader a bad choice, because there are just thousands of them on the net and imho it doesn't help you learning assembler. It's just plain&simple frustrating.
But back to your question
Quoting from here:
1. The DOS Boot Record (DBR) is read to determine the size of the DBR, FAT, and Root Directory. The location of each on the disk is then determined.
2. The Root Directory is read in to memory.
3. The Root Directory is searched for the file name LOADER.BIN. If found, we can look in the directory entry to find out which is the file?s first cluster (file allocation unit). If not found, we give an error message.
4. The File Allocation Table is read off the disk in to memory.
5. Starting with the file?s first cluster, we use the FAT to locate all the clusters belonging to the file. We read them all off the disk into memory at a specific location.
6. We jump to that location to begin execution of the operating system.
I also think that fat is a bad choice, because it's limitations (8 letter names + 3 extension, only capital letters, ...). On the other hand it's one of the simplest filesystems on earth and it's supported by microsoft and it's specification is freely available. I plan to use ext2/3 or reiserfs as root filesystem.
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Cjmovie
Re:16Bit FAT12
Two things:
First, I agree with bluecode. Although I'd like to add the best of the avaliable ones that could do your job would have to be GRUB:
http://www.osdev.org/osfaq2/index.php/GRUB
Second, Fat12 is not 16bits, it's 12 bits
. 16 bit FAT, however, would be FAT16.
Oh, one other thing. You aren't restrained to capitals or 8.3 filenames, IF you wish to support the LFN extension to FAT.
However, for me, I made a very simple 'root/boot' filesys. If you'd like, I could also provide it, but I would't recommend it....
First, I agree with bluecode. Although I'd like to add the best of the avaliable ones that could do your job would have to be GRUB:
http://www.osdev.org/osfaq2/index.php/GRUB
Second, Fat12 is not 16bits, it's 12 bits
. 16 bit FAT, however, would be FAT16.Oh, one other thing. You aren't restrained to capitals or 8.3 filenames, IF you wish to support the LFN extension to FAT.
However, for me, I made a very simple 'root/boot' filesys. If you'd like, I could also provide it, but I would't recommend it....
Re:16Bit FAT12
Before you start to sense a pattern, FAT32 is 28 bits.Cjmovie wrote: Second, Fat12 is not 16bits, it's 12 bits
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Cjmovie
Re:16Bit FAT12
Yeah, thought It would be a bad idea to include that in my list though, because of thatCandy wrote:Before you start to sense a pattern, FAT32 is 28 bits.Cjmovie wrote: Second, Fat12 is not 16bits, it's 12 bits
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bluecode
Re:16Bit FAT12
who said that FAT12 is 16 bit?
[edit: lol. I'm blind ;D the topic...]
btw. 2 + 2 doesn't equal 5, I think
[edit: lol. I'm blind ;D the topic...]
btw. 2 + 2 doesn't equal 5, I think
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Cjmovie
Re:16Bit FAT12
Really? I could have swore.
http://www.thinkgeek.com/tshirts/generic/60f5/
http://www.thinkgeek.com/tshirts/generic/60f5/
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Vladaz
Re:16Bit FAT12
By saying 16bit i meant Real mode, not the Fat16:) sorry for that:)
Thanks for help, i will try to use maybe GRUB, or I will continue with my own. But if I will want tu use VESA, does the GRUB has the support of it?
Thanks for help, i will try to use maybe GRUB, or I will continue with my own. But if I will want tu use VESA, does the GRUB has the support of it?
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bluecode
Re:16Bit FAT12
hi
yes, the multiboot specification should support switching the video resolution, but personally I never got it working. I don't know why, perhaps someone can explain how to do it.
But if your in real-mode, than you can use BIOS Interrupt 0x10. If you're in protected-mode you could use interrupt 0x10 in virtual-8086-mode or you can use the protected-mode interface of the VBE (=Video BIOS Extension). You should look into the VBE Specification 2.0/3.0 for more information.
perhaps lim(2+2) = 5 for 2 -) 2.5
yes, the multiboot specification should support switching the video resolution, but personally I never got it working. I don't know why, perhaps someone can explain how to do it.
But if your in real-mode, than you can use BIOS Interrupt 0x10. If you're in protected-mode you could use interrupt 0x10 in virtual-8086-mode or you can use the protected-mode interface of the VBE (=Video BIOS Extension). You should look into the VBE Specification 2.0/3.0 for more information.
perhaps lim(2+2) = 5 for 2 -) 2.5