Diagnostics and System Management Services 167
6.5.1.1 Identify and Configure System Components
The firmware must, by various means, become aware of every component in
the system and configure or reset those components into a known state.
Components include all bridges and device controllers, but may exclude
devices that are not involved in the boot process.
Firmware is generally written with a hardware platform in mind so that some
components and their configuration data can be hardcoded. Examples of
these components are: number and type of processors, cache
characteristics, and the use of components on the planar. This hardcoding is
not a requirement, only a practical approach to a part of this task.
Certain system information must come from walking the I/O buses. This is a
technique that will yield identification of I/O device controllers and bridges
that reside on modern, well-behaved buses such as PCI.
6.5.1.2 Generate a Device Tree
The firmware will build a device tree. Certain configuration information
(configuration variables) may be stored in non-volatile memory.
6.5.1.3 Initialize/Reset System Components
The AIX operating system requires devices to be in a known state at the time
control is transferred from the firmware. Firmware may gain control of the
hardware in various states depending on what has initiated the boot process.
6.5.1.4 Locate an OS Boot Image
A device and filename can be specified directly from the AIX boot command.
Once the boot image is located, the device path is set in the device tree as
the bootpath property of the chosen node.
If multi-boot (multiple bootable operating systems residing on the same
hardware platform) is supported, a configuration variable instructs the
firmware to display a multi-boot menu from which the OS and bootpath are
selected.
6.5.1.5 Load the Boot Image into Memory
After locating the image, it is loaded into memory at the location given by a
configuration variable or as specified by the OS load image format.
6.5.2 Typical Boot Sequence for RS/6000 43P 7043 Model 150
After the system unit power is turned on, the system firmware tests the
system memory and identifies failing memory cards and memory module
locations. System firmware checks to see what devices are in the system and