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Intel® PXA255 Processor Developer’s Manual 13-1
AC’97 Controller Unit 13
13.1 Overview
The AC’97 Controller Unit (ACUNIT) of the PXA255 processor supports the AC’97 revision 2.0
features listed in Section 13.2. The ACUNIT also supports audio controller link (AC-link). AC-
link is a serial interface for transferring digital audio, modem, mic-in, CODEC register control, and
status information.
The AC’97 CODEC sends the digitized audio samples that the ACUNIT stores in memory. For
playback or synthesized audio production, the processor retrieves stored audio samples and sends
them to the CODEC through the AC-link. The external digital-to-analog converter (DAC) in the
CODEC then converts the audio samples to an analog audio waveform.
This chapter describes the programming model for the ACUNIT. The information in this chapter
requires an understanding of the AC’97 revision 2.0 specification.
Note: The ACUNIT and the I
2
S Controller cannot be used at the same time.
13.2 Feature List
The processor ACUNIT supports the following AC’97 features:
• Independent channels for stereo Pulse Code Modulated (PCM) In, Stereo PCM Out,
modem-out, modem-in and mono mic-in
All of the above channels support only 16-bit samples in hardware. Samples less than 16 bits
are supported through software.
• Multiple sample rate AC’97 2.0 CODECs (48 kHz and below). The ACUNIT depends on the
CODEC to control the varying rate.
• Read/write access to AC’97 registers
• Secondary CODEC support
• Three Receive FIFOs (32-bit, 16 entries)
• Two Transmit FIFOs (32-bit, 16 entries)
The processor ACUNIT does not support these optional AC’97 features:
• Double-rate sampling (n+1 sample for PCM L, R & C)
• 18- and 20-bit sample lengths