Audio Codec '97

AC ‘97 Component Specification Revision 2.3 Rev 1.0
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purpose. Recommended bit definitions are provided for maximum interoperability, and should be followed
wherever possible.
The suggested use for the International Bits 1-3 is to implement LINE12_AC, LINE12_DC, and LINE12_RS,
which, when set to one, adjust the DAA AC impedance, DC impedance, and Ring Detect sensitivity to alternate
values more suitable for some non-North American countries. These outputs have effect on both Line 1 and Line 2
(it is assumed that both DAAs reside in the same country).
Outputs LINE1_PULSE and LINE2_PULSE control pulse dial relays, separate from the Off Hook relays, used in
DAAs for some non-North American DAAs.
GPIO_INT has been added to build upon the logic that has already been implemented within the Codec to detect a
change in GPIO input state and trigger a wake-up event. When the Codec is NOT in power-down mode any input
GPIO change can be enabled by the wake-up mask to generate GPIO_INT=1, to indicate to the controller or driver
that the GPIO state has changed and should be updated in memory. The controller acknowledges and clears a wake-
up event or GPIO_INT by writing a 0 to the corresponding bit in Register 54h. This supports shadowing of Codec
registers in memory by potentially eliminating polling.
6.4 Modem Codec Cost Reduction Options
6.4.1 Elimination of the On-board Modem Speaker
Modem subsystems currently rely on an on-board speaker for call progress monitoring. Routing call signals through
the system speakers enables cost reduction via elimination of the redundant speaker. There is a hardware-dependent
analog solution and a hardware-independent digital solution (which supports analog or USB speakers).
• Analog solution: The system designer can route an analog mix of the modem Tx and Rx signals through
PHONE input of the AC '97 analog mixer. This requires that the modem control task have access to AC ‘97
audio driver interface PHONE volume and mute controls, and introduces a dependency on the user’s
preferred master audio volume and mute settings
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(which the modem driver should not attempt to access).
• Digital solution: The modem driver designer can route digital copies of the modem Rx (ADC) and Tx
(DAC) streams (or perhaps just the digitized pre-echo-canceled modem Rx stream from the ADC) into the
system-wide software audio mixer. As with the analog solution, this introduces a dependency on the user’s
preferred master audio volume and mute settings. For this technique to be cost-effective a soft modem
implementation is probably required.
For soft modem implementations AC ‘97 2.2 recommends the digital call progress monitoring solution
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.
6.4.2 Internal PHONE and MONO_OUT Connections (AMC ‘97 )
The AC ‘97 PHONE input was designed to support monitoring of analog telephony signals, such as speakerphone or
call progress, through the audio subsystem and speakers. The AC ‘97 MONO_OUT was designed to support
routing of analog system audio signals (PHONE and PC_BEEP excluded) to the modem subsystem.
Prior to controller-less modems and low latency digital audio, support for voice required:
1.
controller functionality to encode and decode digital voice data
2. a dedicated voice Codec
3.
analog connections between the modem and audio subsystems
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Depending on the OS driver model, access to the analog mixer topology may be supported via standard interface
calls. These calls allow access to mixer mute/volume controls and eliminate the need for a proprietary audio driver
interface. Refer to the appropriate OS Audio Device Class Reference Specifications.
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The digital solution isolates the final call progress rendering hardware. The analog solutions do not lend
themselves easily to audio upgrades or the use of USB speaker solutions. Refer to the appropriate OS Audio Device
Class Reference Specifications