We debugged this over IRC earlier today, and we found that the crash occurs in the int13 call to read a sector from the disk. All previous operations with int13 (detecting the availability of the "extended read" feature, and reading the drive capacity) work fine, but trying to read a sector from the disc will reboot the machine. Working with other drives in the system which are not attached to the SATA card works fine. So it could be a bug in the card's BIOS, or a problem with the parameters we give to it.
