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Architecture

This chapter describes the architecture of the PowerBook G4 17-inch computer. It includes information about the major components on the main logic board: the microprocessor, the other main ICs, and the buses that connect them to each other and to the I/O interfaces.

In this section:

Block Diagram and Buses
Microprocessor and Caches
Intrepid Controller and Buses
I/O Controller

Block Diagram and Buses

This section is an overview of the major ICs and buses on the computer’s main logic board.

Block Diagram

Figure 2-1 is a simplified block diagram of the main logic board. The diagram shows the input and output connectors, the main ICs, and the buses that connect them together.

Main ICs and Buses

The architecture of the PowerBook G4 17-inch computer is designed around the PowerPC G4 microprocessor and Intrepid IC that contains the memory controller and I/O device controller.

The PowerPC G4 microprocessor is connected to the Intrepid IC by a MaxBus bus. The bus clock speed is 167 MHz. Other buses that connect with the Intrepid IC are summarized in Table 2-1, which is in the section “Intrepid Controller and Buses.”

The Intrepid I/O controller has a 32-bit PCI bus with a bus clock speed of 33 MHz. That bus also connects to the Boot ROM and the CardBus controller. The Intrepid IC has other buses that connect with the hard disk drive and the optical drive, the power controller IC, the sound IC, the internal modem module, and the wireless LAN module.

Each of the components listed here is described in one of the following sections.

Microprocessor and Caches

The microprocessor communicates with the rest of the system by way of a 64-bit MaxBus bus to the Intrepid IC. The microprocessor has a separate bus to its internal second-level cache.

PowerPC G4 Microprocessor

The PowerPC G4 microprocessor used in the PowerBook G4 17-inch computer has many powerful features, including an efficient pipelined system bus called MaxBus.

Features of the PowerPC G4 include

• 32-bit PowerPC implementation

• superscalar PowerPC core

• Velocity Engine (AltiVec technology): 128-bit-wide vector execution unit

• dual 32 KB instruction and data caches

• an on-chip level 2 (L2) cache consisting of 256 KB with a clock speed ratio of 1:1

• high bandwidth MaxBus (also compatible with 60x bus)

• fully symmetric multiprocessing capability

The PowerPC G4 microprocessor in the PowerBook G4 17-inch computer runs at a clock speed of 1 GHz.

Level 2 Cache

The data storage for the L2 cache consists of 256 KB of fast static RAM that is built into the microprocessor chip along with the cache controller and tag storage. The built-in L2 cache runs at the same clock speed as the microprocessor.

Level 3 Cache

The data storage for the L3 cache is 1 MB of DDR SRAM running at a clock speed ratio of 5:1. The tag storage for the L3 cache is built into the microprocessor.

Intrepid Controller and Buses

The Intrepid IC provides cost and performance benefits by combining several functions into a single IC. It contains the memory controller, the PCI bus bridge, the Ethernet and FireWire interfaces, and the AGP interface.

Each of the separate communication channels in the Intrepid IC can operate at its full capacity without degrading the performance of the other channels.

In addition to the buses listed in Table 2-1, the Intrepid IC also has separate interfaces to the physical layer (PHY) ICs for Ethernet and FireWire, and an IIC (inter-IC control bus) interface that is used for configuring the memory subsystem.

The microprocessor and the I/O controller IC are described in their own sections. The following sections describe the other subsystems that are connected to the Intrepid IC.

System RAM

The memory subsystem in the PowerBook G4 17-inch computer supports two slots for 333 MHz DDR (PC2700) SO-DIMMs (small-outline dual inline memory modules). The data bus to the RAM and DIMM is 64 bits wide, and the memory interface is synchronized to the MaxBus bus interface at 167 MHz. See “RAM Expansion Slots.”

Boot ROM

The boot ROM is connected to the Intrepid IC by way of the high byte of the PCI bus plus three additional control signals: chip select, write enable, and output enable. The boot ROM is a 1 MB by 8 bit device.

FireWire Controllers

The Intrepid IC FireWire controller supports IEEE 1394a for a maximum data rate of 400 Mbps (50 MBps) and IEEE 1394b for a maximum data rate of 800 Mbps (100 MBps). The Intrepid IC provides DMA (direct memory access) support for the FireWire interface.

The controller in the Intrepid IC implements the FireWire link layer. A physical layer IC, called a PHY, implements the electrical signaling protocol of the FireWire interface and provides the electrical signals to the port. For more information, see “FireWire 400 Connector” and “FireWire 800 Connector.”

Ethernet Controller

The Intrepid IC includes an Ethernet media access controller (MAC) that implements the link layer. The Intrepid IC provides DB-DMA support for the Ethernet interface.

The Ethernet controller in the Intrepid IC is connected to a PHY interface IC that provides the electrical signals to the port. The PHY is capable of operating in either 10Base-T, 100Base-T, or 1000Base-T mode: The actual speed of the link is automatically negotiated by the PHY and the bridge or router to which it is connected. For more information, see “Ethernet Port.”

The PHY supports Auto-MDIX, which allows the use of straight-through cables in crossover situations (and conversely). For more information, see “Ethernet Port.”

Video Display Subsystem

The video display subsystem contains the graphics controller IC along with 64 MB of DDR SDRAM memory. The graphics IC, an nVidia GeForce4 440 Go, contains 2D and 3D acceleration engines, front-end and back-end scalers, a CRT controller, and an AGP4x bus interface with bus master capability.

The features of the nVidia GeForce4 440 Go include

• graphics processor clock speed of 189 MHz

• memory clock speed of 202.5 MHz

• support for 64 MB of DDR video memory with 128-bit interface

• 2D and 3D graphics acceleration

• transform acceleration

• lighting acceleration

• video acceleration

• support for MPEG decoding

• support for video mirror mode

• support for dual-display mode

• S-video output for a TV monitor

The interface between the graphics IC and the rest of the system is an AGP4x (accelerated graphics port, quadruple speed) bus on the Intrepid IC. The AGP bus has 32 data lines, a clock speed of 66 MHz, and supports deeply pipelined read and write operations.

The graphics IC uses a graphics address remapping table (GART) to translate AGP logical addresses into physical addresses. The graphics driver software can allocate memory in both the graphics SDRAM and the main memory.

The graphics IC supports the internal flat-panel display and an external monitor. The external monitor can either mirror the built-in display or show additional desktop space (dual-display mode). For information about the displays and supported resolutions, see “Flat-Panel Display” and “External Monitors.”

I/O Controller

The I/O controller IC in the PowerBook G4 17-inch computer is a custom IC called Intrepid. It provides the interface and control signals for the devices and functions described in the following sections.

DMA Support

The Intrepid IC provides DB-DMA (descriptor-based direct memory access) support for the following I/O channels:

• Ultra DMA ATA interface to the the internal hard drive

• modem slot interface to the built-in modem

• IIS channel to the sound IC

The DB-DMA system provides a scatter-gather process based on memory resident data structures that describe the data transfers. The DMA engine is enhanced to allow bursting of data files for improved performance.

Interrupt Support

The Intrepid IC has an interrupt controller (MPIC) that handles interrupts generated within the IC as well as external interrupts, such as those from the Ethernet and FireWire controllers.

USB Interface

The Intrepid IC implements three independent USB controllers (root hubs), two of which are each connected to one of the ports on the side of the computer. The use of independent controllers allows both USB ports to support high data rate devices at the same time with no degradation of their performance. If a user connects a high-speed (12 Mbps) device to one port and another high-speed device to the other, both devices can operate at their full data rates.

The third independent USB controller supports the internal modem and Bluetooth modules.

The two external USB connectors support USB devices with data transfer rates of 1.5 MBps (12 Mbps). For more information about the connectors, see “USB Connectors.”

USB devices connected to the PowerBook G4 17-inch computer are required to support USB-suspend mode as defined in the USB specification. Information about the operation of USB-suspend mode on Macintosh computers is included in the Mac OS USB DDK API Reference. To obtain it, see the reference at “USB Interface.”

The USB ports on the PowerBook G4 17-inch computer comply with the Universal Serial Bus Specification 1.1 Final Draft Revision. The USB controllers comply with the Open Host Controller Interface (OHCI) specification.

Ultra ATA-100 Interface

The Intrepid IC provides an Ultra ATA-100 channel that is connected to the internal hard disk drive. The Intrepid IC provides DB-DMA (descriptor-based direct memory access) support for the ATA-100 interface.

The internal hard disk drive is connected as device 0 (master) in an ATA Device 0/1 configuration. For more information, see “Hard Disk Drive.”

ATA-33 Interface

The Intrepid IC provides an ATA bus that supports the SuperDrive (DVD-R/CD-RW) drive and the wireless LAN module. The SuperDrive is an ATAPI drive and is device-selected as master in an ATA device configuration.

Modem Support

The internal modem is connected to an internal USB port. The Intrepid IC provides DB-DMA support for the modem interface. The modem provides digital call progress signals to the sound circuitry.

The internal modem is a separate module that contains the data pump IC and the interface to the telephone line (DAA). For more information about the modem, see “Internal Modem.”

Sound Circuitry

The sound circuitry, called Snapper, is connected to the Intrepid IC by a standard IIS (inter-IC sound) bus. The Intrepid IC provides DB-DMA (descriptor-based direct memory access) support for the IIS port.

The Snapper circuitry includes a signal processing IC that handles the equalization and volume control functions, a codec IC that performs A-to-D and D-to-A conversion, and a power amplifier that drives the headphone jack.

All audio is handled digitally inside the computer. The Snapper circuitry performs digital-to-analog conversion for the audio signals to the internal speakers and the headphone jack.

For a description of the features of the sound system, see “Sound System.”

Power Controller

The PowerBook G4 17-inch computer can operate from a 15 volt power outlet on an airline, but for safety reasons, the computer will not allow battery charging. In order for the computer to detect the connection to airline power, the airline power cable should have a sense resistor of 24.3 K ohms +/-1% connected between the power plug's shell and ground.

The PowerBook G4 17-inch computer has a variable speed fan control circuit and a thermal circuit that will force the unit into reduce-processor mode at 72 degrees Celsius and into sleep mode if the processor temperature exceeds 79 degrees Celsius.

The power management controller in the PowerBook G4 17-inch computer is a custom IC called the PMU99. It supports several power-saving modes of operation, including idle, doze, and sleep.

A device’s ID voltage limits determines how the PMU identifies the power adapter. The PowerBook G4 17-inch computer is designed to use the 65-Watt Apple Portable Power Adapter which ships with it. Although you can use a 45-Watt Apple portable power adapter with a 17-inch PowerBook G4 computer, it may not provide sufficient power during some activities and power may be drawn temporarily from the battery. Should the battery become discharged, you may need to plug in the 65-Watt Apple Portable Power Adapter that came with the computer in order to start it up.

AirPort Extreme Interface

AirPort Extreme contains a media access controller (MAC), a digital signal processor (DSP), and a radio-frequency (RF) section.

Two antennas are built into the computer’s case. To improve reception, a diversity module between the antennas and the card measures the signal strength from both antennas and selects the stronger signal for AirPort Extreme.

AirPort Extreme is based on the IEEE draft specification of the 802.11g standard. The card transmits and receives data at up to 54 Mbps and is compatible with 802.11b-standard 11 Mbps systems and older 802.11b-standard systems. For information about its operation, see “AirPort Extreme.”

CardBus Controller IC

The interface to the PC Card slot is connected to the PCI bus. The CardBus controller IC is a PCI1510A device made by Texas Instruments. It supports both 16-bit PC Cards and 32-bit CardBus Cards.

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