How It Works

• 32-bit mode from the start: load GDT and enable memory protection

  • execute LGDT instruction and provide a pointer to a table descriptor
  • no problem with having the table in NVRAM - takes about 10 instructions

• Basic chipset initialization

  • assembly code needed to turn DRAM on
  • the rest can be done in C

• Linux assumes hardware is initialized by BIOS. LinuxBIOS cannot assume this

  • e.g. if IDE controller is not initialized then Linux assumes that BIOS disabled it
  • one-line change to make the driver enable IDE by default

• 5 major components:

  • protected mode setup
  • DRAM setup
  • transition to C
  • mainboard fixup
  • Kernel unzip and jump to kernel