I am new to OS design, and so far have designed one "OS" (Really just a single bootsector), and have decided to try to make a distinct bootloader and "kernel" (still very simple). My question is simple, yet has managed to elude me, through googling, and searching this site (okay, I did find one similar question, but the answer was to vague / advanced for me to be able to use it).
I've looked at int 0x13 AH=02, but that uses tracks, which I don't think CD's use. I saw somewhere that I should use extended read sector (AH=0x42), but I don't see how to use it, because I don't see where I can specify which sector to read, and where the sector should go in RAM.
Here is the question: How do I load sectors from a CD that uses El Torito no emulation. I would appreciate it if you could put the answer in 'simplest form', and try to provide some code, as I am new to this. Thanks in advance!
EDIT:
I don't know if you need it, but I'm using NASM syntax, so if you could give me the answer in NASM, that would be great.
By convention, the BIOS puts the drive number you should use for int 13h into the DL register. Then you can use int 13h, ax=4B01h (get emulation status) to determine the disk info, and int 13x function 42h to read 0x800-sized CD sectors with the sector number in the LBA field. Check the ISOLINUX bootloader for more details. Entrypoint is _start, routine to read sectors is getlinsec_cdrom.
Edit: read the documentation on int 13h extensions about how to use it. Basically, you need to pass a filled structure, with the sector number, count, and address of the buffer where to put the read data.