Intel ITANIUM ARCHITECTURE - SOFTWARE DEVELOPERS MANUAL VOLUME 1 REV 2.3 Manual page 873

The UEFI Boot Manager displays the list of operating system choices and permits the
user to select the operating system for booting. To support this functionality, the OS
setup program stores the boot paths of the OS loaders and boot options in non-volatile
storage managed by the UEFI firmware. The UEFI reserves the environment variables
Boot#### (#### represents values 0000 to 0xFFFF) for this purpose. The OS setup
program must also store the OS loader binary images within the UEFI System Partition.
The UEFI Boot Manager will also allow the user to add boot options, delete boot options,
launch an UEFI application, and set the auto-boot time out value.
The UEFI System Partition also contains UEFI drivers that may be loaded by the UEFI
firmware prior to transfer of control to an OS loader. The floating-point software assist
(FPSWA) library is included in a UEFI runtime driver. The FPSWA library may be invoked
by the OS during floating-point exception faults and traps. Please see
"Software Assistance Exceptions (Faults and Traps)" on page 2:587
information on the usage of this library.
If the user elects to boot an Itanium architecture-based operating system, the UEFI
loads the appropriate OS loader from the UEFI System Partition and passes control to
it. The OS loader will load other files including the OS kernel from an OS partition using
the UEFI boot services which provides an API interface to the OS loader.
The OS loader can obtain information about the memory map usage of the firmware by
making the UEFI procedure call GetMemoryMap(). This procedure provides information
related to the size and attributes of the memory regions currently used by firmware.
The OS loader will then jump to the OS kernel that takes control of the system. Until
this point, system firmware retained control of key system resources such as the
Interrupt Vector Table and provided the necessary interrupt, trap and fault handlers.
Figure 13-2, "Control Flow of Boot Process in a Multiprocessor Configuration" on page
2:626 depicts the booting steps in a MP configuration.
13.1.2 Operating System Boot Steps
The firmware will initialize the processor(s) and platform to a specific state before
handing off to the operating system boot loader. The boot loader is then responsible for
copying the operating system from some storage medium into memory for running.
Once this is done the operating system will need to initialize some key registers before
entering into a higher level language code such as C. This section will describe code
that an OS will need to execute in order to initialize system registers for preparing an
OS to run in virtual mode and handle interrupts.
the Itanium architecture-based sample assembly code described in this section.
Assuming the specific operating system boot loader hands off to the OS kernel in
physical mode, the operating system should first disable interrupts and interrupt
collection via the PSR. This is done to avoid taking external interrupts from timers, etc
and also prepares for writing specific system registers that require PSR.ic to be 0 when
written.
Volume 2, Part 2: Firmware Overview
Section 8.1.1,
for more
Appendix A, "Code Examples" provides
2:625