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AC ’97 Programmer’s Reference Manual 39
4 Surround Audio Support
The AC ’97 Component Specification allows for up to six channels of audio supported in the AC-
link. The audio device driver must determine the number of audio channels available in the
codec(s) and properly enable the ICH5 AC ’97 controller to support those channels in the link.
4.1 Determine Codec’s Audio Channels
Upon determination of the link topology, system software must proceed to resolve the total
number of audio channels available in the codec(s). Appendix A of the AC ’97 Component
Specification, Revision 2.1 defines codec register index 28h to indicate the presence of surround,
center and LFE channels as follows: Extended Audio ID Register (Index 28h).
Table 18. Extended Audio ID Register
Bit D6: CDAC=1 indicates optional PCM Center DAC is supported
Bit D7: SDAC=1 indicates optional PCM Surround L and R DACs are supported
Bit D8: LDAC=1 indicates optional PCM LFE DAC is supported
Bit D9: AMAP=1 indicates optional slot/DAC mappings based on Codec ID (Refer to the AC ’97
Component Specification, Revision 2.1, Appendix D for description)
Bit D15-D14: ID1, ID0 is a 2-bit field which indicates the Codec configuration: Primary is 00;
Secondary is 01, 10, or 11 (Refer to the AC ’97 Component Specification, Revision 2.1
Appendix C for details)
The AC ’97 Component Specification, Revision 2.3, Section 5.8.2, provides detailed information
on the usage model for multiple audio channels. This specification assumes the proper use of the
AMAP bit describes the partition of the channels exposing critical functionality. If AMAP bit is
not set to “1” a generic driver will not be able to determine the proper codec to slot distribution for
a split audio codec configuration.
Based on Table 32 of the AC ’97 Component Specification, Revision 2.3, the following table
describes the available codec topology to audio channel distribution for ICH5 AC ’97 controller.
Table 19. Single Codec Audio Channel Distribution
Single Audio Codec Configuration
Primary Total Audio Channels
L/R 2
L/R; S-L/R 4
L/R; S-L/R; C/LFE 6