Apple iMac - Manual (Page 63)

C H A P T E R 5
Software
NewWorld Boot Process 63
Trampoline Code 5
The Trampoline code is the component of the NewWorld architecture that
handles the transition between Open Firmware and the ToolBox ROM Image. It
retrieves all necessary information about the system from Open Firmware,
instantiates RTAS, decompresses the ToolBox ROM Image, locates the Mac OS
NV-RAM partition, formats the system information into tables and data
structures for Mac OS, terminates Open Firmware, moves information in
memory to safe locations, and transfers control to the ToolBox ROM Image.
ToolBox ROM Image 5
The NewWorld version of the ToolBox ROM Image is similar to the old ToolBox
ROM in that it has a similar layout and contains many of the same components
as it did before.
The ToolBox ROM Image includes code that contains hardware-specific
support, including ADB, VIA, Cuda/Egret, MESH SCSI, Heathrow/CHRP/
UltraDMA ATA AIMs. In the future, they can be moved out of the ToolBox
ROM Image when there is a mechanism to load them from a boot volume at
boot time.
NewWorld Boot Process 5
Following is a high level view of the execution path take when a
NewWorld-based computer boots.
1. The POST code runs (preliminary diagnostics, boot beep, initialization, and
setup), with possible intervention in the Mini Nub.
2. Open Firmware initializes and begins execution, including building the
device tree and the interrupt trees;
3. Open Firmware loads the Toolbox image file, based on defaults and NV-RAM
settings;
4. Open Firmware executes the Forth script in the bootinfo file, which contains
instructions to read both the Trampoline code and the compressed ToolBox
ROM Image and place them into a temporary place in memory;