Apple Desktop Computer manual Mac OS ndrv Drivers, Rtas

Page 61

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.

Boot ROM Contents

61

Image 61

Contents Apple iMac Computer Page Contents RAM Expansion Devices and PortsRtas SoftwareRtas NV-RAM Appendix Abbreviations IndexFigures and Tables Page About This Developer Note Contents of This NoteSupplemental Reference Documents PowerPC G3 MicroprocessorMac OS ATA DevicesOpen Firmware USB DevicesE F a C E Introduction Features Shows a front view of the computer Case and External FeaturesFront view 2Side view showing I/O bay System Software Compatibility IssuesVideo RAM Expansion Modules Main RAM Expansion ModulesUSB Ports and Devices Page Architecture Architecture G3 Microprocessor Processor moduleBackside Cache Memory Controller and PCI Bridge Main Logic BoardController IC Video Display Subsystem USB ControllerBuilt-in Modem Infrared Link Module Devices and Ports USB Ports USB ConnectorsGND Transfer Types SupportedADB Compatibility USB Compatibility IssuesMacintosh-To-Macintosh Connections Serial Port CompatibilityUSB Storage Devices USB ControllerKeyboard Layout KeyboardKeyboard and USB MouseVideo Display Hard Disk DriveSound System Infrared Communication LinkSound Outputs Sound InputsBuilt-in Microphone External Sound InputExternal Sound Output Sound SpeciﬁcationsHeadphone Jacks Total harmonic distortion Internal Modem Ethernet PortPage RAM Expansion Expansion Slots Removing the Logic Board AssemblyPlacing the Computer Face Down Unfastening the Cables Removing the bottom coverRAM Expansion Removing the Retaining Screws 3Logic board assembly handle and retaining screwsRemoving the EMI Shield Removing the Logic Board AssemblyLocations of the Expansion Slots 6Locations of the RAM expansion slots Main RAM ExpansionElectrical Design of RAM SO-DIMMs Mechanical Design of RAM SO-DIMMsSdram Devices Conﬁguration of RAM SO-DIMMs Address Multiplexing RAM SO-DIMM Electrical LimitsVideo RAM Expansion Page Software Why Make This Change? What Has Changed Features of the New Approach RAM Footprint PerformanceUser Experience Data Structures and FilesBoot ROM Contents Rtas Mac OS ndrv DriversToolbox Image File Contents Trampoline Code NewWorld Boot ProcessToolBox ROM Image Interrupt Handling What Is DifferentRAM Footprint Outmoded ResourcesStartup Disk Control Panel NanoKernelInterrupt Layout Open Firmware and the Device TreeMachine Identiﬁcation Software Abbreviations Chrp NMI Page Index Nvram X, Y, Z Allen Watson