Specifications

Sound System Overview

The sound circuitry is connected to the K2 IC by a standard I2S (inter-IC sound) bus. The K2 IC provides DB-DMA

(descriptor-based direct memory access) support for the I2S port.

The Power Mac G5 circuitry consists of two main components: an analog audio CODEC IC and a digital audio

CODEC IC. The analog audio CODEC IC includes an A/D converter, a D/A converter, and digital audio processing

functions. The digital audio processing functions include output equalization, dynamic range compression,

and volume control. The equalization and dynamic range control functions are set to fixed values to equalize

the internal speaker. Those functions are bypassed for signals sent to the audio output jacks.

Stereo signals from the audio input jack are routed to an analog line input buffer that drives the internal A/D

converter in the analog CODEC. The output of the A/D converter is routed to the K2 IC over the I2S bus.

Digital audio data from the K2 IC is routed to the D/A converter on the analog audio CODEC over the I2S bus.

The analog audio output from the D/A converter is routed to separate amplifiers that drive the line output,

headphone output, and internal speaker.

The digital audio CODEC IC includes an S/PDIF (Sony/Phillips Digital Interface) digital audio receiver, a sample

rate converter (SRC), a phase-locked loop (PLL), and an S/PDIF digital audio transmitter.

The S/PDIF input can operate in synchronous and asynchronous modes. In synchronous mode, the PLL in the

digital audio CODEC locks on to the incoming S/PDIF data rate and drives the audio system clocks in the Power

Mac G5, allowing bit-accurate data processing of the S/PDIF input data. In asynchronous mode, the incoming

S/PDIF data passes through the SRC, where it is converted to the output sample rate of the Power Mac G5,

allowing the Power Mac G5 to play audio at a fixed output sample rate while accepting S/PDIF input data over

a wide frequency range. The audio data from the S/PDIF receiver is routed to the K2 IC over the I2S bus.

Digital audio data from the K2 chip is routed to the S/PDIF output transmitter in the digital audio CODEC over

the I2S bus. The Power Mac G5 sends and receives S/PDIF audio data over TOSLink optical connectors.

Analog audio I/O is not independent of digital audio I/O on the Power Mac G5. Audio input can come from

either the line input or the S/PDIF input, but not both at the same time. Audio output can be played

simultaneously on the line out, headphones output, and S/PDIF output. However, these audio streams are not

independent.

The speaker output is mutually exclusive from the line out, headphones out and S/PDIF outputs. If the speaker

output is selected, the line output, the headphones output and the S/PDIF output are disabled. If any of the

line output, the headphones output, or the S/PDIF output are selected, the speaker output is disabled.

When the speaker output is active, the digital audio processing functions in the analog CODEC are used to

implement output equalization for the internal speaker, resulting in improved sound quality from the internal

speaker.

Architecture

K2 I/O Controller