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Chapter 5 Input/Output Interfaces
5.8.5 AUDIO PROGRAMMING
Audio subsystem programming consists configuration, typically accomplished during POST, and
control, which occurs during runtime.
5.8.5.1 Audio Configuration
The audio subsystem is configured according to PCI protocol through the AC’97 audio controller
function of the 82801 ICH2. Table 5-21 lists the PCI configuration registers of the audio
subsystem.
Table 5–21. AC’97 Audio Controller PCI Configuration Registers
Table 5-21.
AC’97 Audio Controller
PCI Configuration Registers (82801 Device 31/Function 5)
PCI
Conf.
Addr.
Register
Value
on
Reset
PCI
Conf.
Addr.
Register
Value
on
Reset
00-01h Vender ID 8086h 14-17h Native Audio Bus Mstr. Addr. 1
02-03h Device ID 2445h 18-1Bh Reserved 1h
04-05h PCI Command 0000h 1C-2Bh Reserved 1h
06-07h PCI Status 0280h 2C-2Dh Subsystem Vender ID 0000h
08h Revision ID XXh 2E-2Fh Subsystem ID 0000h
09h Programming 00h 30-3Bh Reserved --
0Ah Sub-Class 01h 3Ch Interrupt Line 00h
0Bh Base Class Code 04h 3Dh Interrupt Pin 02h
0Eh Header Type 00h 3E-FFh Reserved 0’s
10-13h Native Audio Mixer Base Addr. 1 -- -- --
5.8.5.2 Audio Control
The audio subsystem is controlled through a set of indexed registers that physically reside in the
audio codec . The register addresses are decoded by the audio controller and forwarded to the
audio codec over the AC97 Link Bus previously described. The audio codec’s control registers
(Table 5-22) are mapped into 64 kilobytes of variable I/O space.
Table 5–22. AC’97 Audio Codec Control Registers
Table 5-22.
AC’97 Audio Codec Control Registers
Offset
Addr. / Register
Value
On
Reset
Offset
Addr. / Register
Value
On
Reset
Offset
Addr. / Register
Value
On
Reset
00h Reset 0100h 14h Video Vol. 8808h 28h Ext. Audio ID. 0001h
02h Master Vol. 8000h 16h Aux Vol. 8808h 2Ah Ext. Audio Ctrl/Sts 0000h
04h Reserved -- 18h PCM Out Vol. 8808h 2Ch PCM DAC SRate BB80h
06h Mono Mstr. Vol. 8000h 1Ah Record Sel. 0000h 32h PCM ADC SRate BB80h
08h Reserved -- 1Ch Record Gain 8000h 34h Reserved --
0Ah PC Beep Vol. 8000h 1Eh Reserved -- 72h Reserved --
0Ch Phone In Vol. 8008h 20h Gen. Purpose 0000h 74h Serial Config. 7x0xh
0Eh Mic Vol. 8008h 22h 3D Control 0000h 76h Misc. Control Bits 0404h
10h Line In Vol. 8808h 24h Reserved -- 7Ch Vender ID1 4144h
12h CD Vol. 8808h 26h Pwr Mgnt. 000xh 7Eh Vender ID2 5340h
5-30 Compaq Evo and Workstation Personal Computers
Featuring the Intel Pentium 4 Processor
Second Edition – January 2003