Audio Codec '97 Revision 2.1

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AC ‘97 Component Specification Revision 2.1 11. AC ’97 2.0 Extensions AC ’97 2.1 Appendix D also includes additions or clarifications for audio, modem, and multiple Codec implementations. 11.1 Introduction In response to requests from audio and modem IHVs as well as PC OEMs, Intel invited Audio Codec ’97 licensees to participate in a Working Group to extend the AC '97 Component Specification to include interoperable definitions for the following functionality: Appendix A: AC ’97 2.0 Variable Sample Rate Extension Appendix B: AC ’97 2.0 Modem AFE Extension Appendix C: AC ’97 2.0 Multiple Codec Extension All of the extensions are defined as optional Appendices to the current AC '97 Component Specification, and are intended to enable future generations of interoperable AC-link-based audio and modem Codecs and Controllers. As with AC '97, the intention is to define a common interoperable high-level feature set, yet provide flexibility for actual implementation. An Extended AC ’97 2.0 Register Summary is provided at the end of the introduction section. The AC ’97 extensions are designed to allow one commonly defined Digital Controller (also referred to as DC ’97) to target a variety of AC-link functionality implemented as • audio only with existing AC ’97 Codec • audio only with extended AC ’97 Codec (also referred to as AC ’97 2.0) • a combo audio modem Codec (also referred to as AMC ’97) • separate Codecs for audio (AC ’97 2.0) and modem (also referred to as MC ’97) • dual Codecs for mobile (AC ’97, AC ’97 2.0, or AMC ’97) and dock (AC ’97 or AC ’97 2.0) • multiple Codecs (one primary and up to three secondary) In addition, the 2-channel extended AC ’97 2.0 audio functionality has been defined to be backward-compatible with current AC ’97 Controllers. 11.2 Overview of Extended AC ’97 2.0 Functionality SYNC SDATA_OUT SDATA_IN Slot # 0 1 2 3 4 5 6 7 8 9 10 11 12 TAG Codec ID TAG CMD ADDR STATUS ADDR SLOTREQ 3-12 CMD DATA STATUS DATA PCM L PCM L PCM R PCM R LINE 1 DAC LINE 1 ADC 56 PCM CENTER MIC ADC PCM L SURR RSRVD PCM R SURR Figure 26. Extended AC ’97 2.0 Slot Definitions PCM LFE RSRVD RSRVD LINE 2 DAC PCM L ( n+1) LINE 2 ADC HSET DAC PCM R (n+1) HSET ADC IO CTRL PCM C (n+1) IO STATUS 11.2.1 AC ’97 2.0 Audio Optional multi-channel audio (CENTER, L and R SURROUND, LFE) assignments for AC-link output slots 6-9 were introduced last year in the AC ’97 FAQ paper, and are included here. Note that the market for 6-channel analog output may be limited to the PC Theater segment and special purpose add-in cards. The majority of PCs with May 22, 1998
AC ‘97 Component Specification Revision 2.1 DVD drives are expected to offer matrix-encoded stereo analog output as well as digital multi-channel output via S/P-DIF, USB, or IEEE 1394. Optional variable sample rate audio extends the AC ’97 architecture to address host-based solutions, similar to those appearing on USB, by minimizing the sample rate conversion (SRC) burden (at least for the initial audio stream). High quality digital SRC and mixing support for both 44.1 and 48 kHz content remain key requirements for supporting multiple audio sources, regardless of Controller architecture (host-based or hardware-accelerated Controllers). Variable sample rate operation is supported via newly-defined sample rate control registers for audio DAC and ADC groups and dedicated SLOTREQ bits in the previously unused LSBs (trailing bits) of input slot 1. If variable sample rate output is supported, the AC ’97 2.0 Codec examines its audio sample rate control registers, the state of its FIFOs, and the incoming SDATA_OUT tag bits at the beginning of each audio output frame to determine which SLOTREQ bits to set active. SLOTREQ bits asserted during the current audio input frame indicate which output slots require data from the AC ’97 Digital Controller in the next audio output frame. For fixed 48 kHz sample rate operation the SLOTREQ bits are always set active and a sample is transferred each frame. If variable sample rate input is supported, the tag bit for each input slot indicates whether valid data is present or not. Optional double-rate audio output. Support is defined for optional 88.2 or 96 kHz DAC operation, but implementation is not recommended at this time. Current DVD implementations for CE and PCs allow 96 kHz audio to be down-sampled to 48 kHz for high quality rendering. However, should higher sample rate audio become a requirement for DVD compatibility, output slots 10-12 have been assigned as optional n+1 sample carriers in order to enable double-rate operation on front (L, C, and R) DAC channels with up to 20-bits (120 dB dynamic range) at 88.2 or 96 kHz. True line level out. It is recommended that new AC ’97 Codecs support a true consumer equipment-compatible (10 K Ohm) line level output that does not change with master volume settings. Built-in (as opposed to external) 32- Ohm headphone drive for the optional HP_OUT has not been widely implemented due to power dissipation limitations of the 48-pin and 64-pin packages selected for AC ’97. It is therefore recommended that headphone drive (if required) be kept external to the Codec, and driven from the same master output that drives the speakers. By redefining HP_OUT as LNLVL_OUT and using the independent volume controls in register 04h, LNLVL_OUT can be set once to provide a fixed 1V RMS (2.8 V peak-to-peak) output level for a 0 dB gain PCM output stream. The optional HP_OUT Common pin is no longer needed, and may be used as a cap or ground pin. Also, 5 V analog (AVdd) operation is preferred to 3.3V, because of the potential impact 3.3 V operation will have on line output levels and SNR. A 2-channel AC ’97 2.0 Codec configured to default to fixed 48 kHz operation should be backward-compatible with current AC ’97 Digital Controllers. The 48-pin package and pin out for the AC ’97 Codec has been widely accepted, and continues to be a recommendation for AC ’97 2.0 audio. 11.2.2 AMC ’97 2.0 Combined Audio and Modem AFE Defined support for modem AFE now includes output and input slot assignments for two lines, a handset, up to 16 GPIO control bits, variable sample rate operation, and wake-up event signaling protocols. Similar to the AC ’97 2.0 audio case, but required for modem, variable sample rate operation is supported via a newly-defined modem sample rate control register for each modem DAC/ADC pair and dedicated SLOTREQ bits in the previously unused LSBs (trailing bits) of input slot 1. For variable sample rate output, the AMC ’97 Codec examines its audio and modem sample rate control registers, the state of its FIFOs, and the incoming SDATA_OUT tag bits at the beginning of each audio output frame to determine which SLOTREQ bits to set active. SLOTREQ bits asserted during the current audio input frame signal which output slots require data from the AC ’97 Digital Controller in the next audio output frame. For variable sample rate input, the tag bit for each input slot indicates whether valid data is present or not. 57 May 22, 1998
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Audio Codec '97 Revision 2.1

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