Technical information

CHAPTER 5

System Software

88 What Is Different

startup include display, keyboard, and mouse devices, and storage devices such

as hard drives and CD-ROM drives.

IMPORTANT

If Open Firmware code is not included in the expansion

card for a startup device, the card will not be usable until

the operating system loads its supporting software from

disk after the startup process has concluded. ▲

For a description of the way startup code in an expansion card’s ROM exports

properties to the Open Firmware device tree, please see Designing PCI Cards and

Drivers for Power Macintosh Computers.

Interrupt Layout 5

The interrupt layout is determined by information in the device tree. An

interrupt tree overlays the other information in the device tree to describe how

the interrupts are conﬁgured. The Trampoline code traverses this device tree

interrupt tree and builds data structures that are used to dispatch interrupts.

The device tree interrupt tree is deﬁned in the Open Firmware Recommended

Practice: Interrupt Mapping. It is not necessary to change any of the interrupt

dispatching code, either 68K or native. All the necessary information is

retrieved from the device tree.

This interrupt dispatch code has drastically reduced latency times as compared

to all previous PCI Macintosh computers.

Machine Identiﬁcation 5

Because the NewWorld architecture uses the same Universal and ProductInfo

tables for all computer models that it runs on, those computers all have the

same Box Flag. All those computers use the same enablers, and no patches are

made to the Mac OS ROM Image, so sharing the same box ﬂag is not an issue

for those areas.

In the past, applications could ﬁnd out which machine they are running on by

using the gestaltMachineType value returned from a call to the Gestalt Manager.

The 1999 PowerBook G3 Series computer and all other computers that use the

NewWorld architecture return the same gestaltMachineType value: 406 ($196 ).