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Overview to eMac Developer Note

This chapter lists the features of the eMac computer and provides information about a few software issues of interest to developers.

In this section:

New Features
All Features
External Features
System Software


New Features

The features that have changed are listed here with links to the sections that describe them.

All Features

Here is a complete list of the features of the eMac computer. Each feature is described in more detail in a later section.

External Features

The eMac computer is housed in a polycarbonate plastic enclosure that includes the display. The separate keyboard and mouse are also designed in polycarbonate plastic.

The front of the enclosure is dominated by the 17 inch flat display. The front also includes, below the display, the following features:

The right side of the enclosure, as viewed from the front, contains the I/O panel. The I/O panel contains the following features:

The receptacle for the power cord is located on the back. The back panel also includes the following features:

The back portion of the bottom of the enclosure has a door that can be opened for access to the expansion RAM. For more information, see “RAM Expansion Slots.”

System Software

The Combo drive and CD-ROM configurations of the eMac computer come with both Mac OS X (originally, version 10.2.4) and Mac OS 9.2.2 installed and bootable. Mac OS X is the default system. The SuperDrive configuration of the eMac computer comes with Mac OS X (originally, version 10.2.4). Customers can run Mac OS 9 applications in Classic.

Note: The AirPort Extreme Card requires Mac OS X drivers and will not work on CD-ROM and Combo drive systems when booted into Mac OS 9.

For more information about Mac OS X, see the reference listed in “Mac OS X.” For the latest information about Mac OS 9.2.2, see the reference listed in “Mac OS 9.2.2.”

Computer Identification

Rather than reading the box flag or the model string and then making assumptions about the computer’s features, applications that need to find out the features of the computer should use IORegistry calls to test for the features they require. IORegistry calls are part of the I/O Kit API. For more information, see the references listed at “I/O Kit.”

Asset management software that reports the kind of computer it is run on can obtain the value of the model property from the IOService plane of the IORegistry. For the eMac, the value of the string in the compatible property is PowerMac4,4.

NMI without Programmer’s Switch

Current Macintosh computers do not have a programmer’s switch, which allowed users to generate a non-maskable interrupt (NMI). The paragraphs below describe how to generate an NMI from a remote session for systems that do not have a physical programmer's switch.

Starting with Mac OS X 10.1.2, the OS will promote and recognize the DB_NMI bit in the “bootargs” property of the “chosen” node from Open Firmware. When the DB_NMI bit is set, the user can generate a non-maskable interrupt (NMI) by pressing the system's power button. This replaces the power button’s sleep or wake response. The system reads the state of the bit at boot time from the boot-args configuration variable. For more information about the debug flags, please see Inside Mac OS X: Kernel Programming.

To set the DB_NMI bit, enter the following command at the Terminal to display the current debug flag settings.

% nvram boot-args

Add the parameter debug=0x4, as follows.

% sudo nvram boot-args="<current settings> debug=0x4"

Press the power button for approximately 3 seconds to reboot and generate an NMI.

Note: If the power button is pressed for more than five seconds, the system will immediately power off.

The power button will retain this functionality until Mac OS X is restarted without the DB_NMI bit set. To clear this bit, issue the nvram command omitting debug=0x4 parameter,, as follows.

% sudo nvram boot-args=""

Note: The debug flags bit will be cleared if you use System Preferences to change the startup disk. It may also be cleared if you perform an installation that requires a restart.

Velocity Engine Acceleration

The Velocity Engine (an implementation of AltiVec) is the vector processing unit in the PowerPC G4 microprocessor. Some system software has been modified to take advantage of the accelerated processing that the Velocity Engine makes possible. System software has also been modified to support low-level operations using the Velocity Engine.

For complete information on the Velocity Engine, refer to the following Apple websites:

http://developer.apple.com/hardwaredrivers/ve/index.html

and

http://developer.apple.com/documentation/Performance/Conceptual/vDSP/vDSP_Library.pdf



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© 2003 Apple Computer, Inc. All Rights Reserved. (Last updated: 2003-06-09)


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