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AC ’97 Programmer’s Reference Manual 39 

 

 

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. 

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). 

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. 

L/R 2 

L/R; S-L/R 

4 

L/R; S-L/R; C/LFE 

6