Apple Desktop Computer manual Mac OS ndrv Drivers, Rtas

C H A P T E R 5

Software

Failure to boot in POST causes the error beep, optionally entering the Mini-Nub.

Open Firmware

The Open Firmware component of NewWorld is based on the CHRP version of Open Firmware, also known as Open Firmware 3.0. This is the most robust and full-featured Open Firmware used by Apple to date. This version of Open Firmware contains several notable changes from the Open Firmware found in the first and second generation PCI Macintosh computers:

■Open Firmware is capable of reliably reading files from block devices.

■Open Firmware builds an expanded device tree that holds every facet of hardware information needed by an operating system.

■Open Firmware contains code that mimics the StartSearch code in the ToolBox ROM and provides a Mac-like user interface during startup.

■Open Firmware creates an interrupt tree that is interlaced through the Device Tree to provide a mechanism to describe the interrupt layout of the computer.

If a boot failure occurs in Open Firmware, Open Firmware attempts to provide a Macintosh-like experience.

Mac OS 'ndrv' Drivers

The Boot ROM may also contain Mac OS drivers that are hardware-specific and needed at boot time; they are organized as 'ndrv' drivers. Drivers needed at boot time (video drivers, network drivers, or disk drivers) need to be loaded from the Device Tree.

RTAS

RTAS (Run-Time Abstraction Services) can be thought of as a BIOS. RTAS code handles hardware accesses needed by an OS, making it possible for multiple operating systems to get hardware services without having to know the specifics. RTAS handles hardware-specific services such as NV-RAM (containing parameter RAM), time services (the real time clock), PCI configuration cycles, power management, and the code needed to restart and shutdown.

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