Audio Codec '97

AC ‘97 Component Specification Revision 2.3 Rev 1.0

while transmitting 48 kHz independent S/PDIF source output, and are compatible with integrated multichannel

audio Controllers.

5.10.1.3 Secondary Codec supports simultaneous DAC playback of a 2-ch 48 kHz PCM stream and S/PDIF

transmission of an independent 48 kHz PCM or encoded multichannel stream

2-ch S/PDIF capable Secondary Codec must accept 48 kHz PCM data on AC-link slots 7&8 for DA conversion and

independent 48 kHz PCM or encoded multichannel data on AC-link slots 6&9 for concurrent S/PDIF transmission.

SPCV must indicate valid configuration when programmed as follows:

• Register 2Ch controlling AC-link slots 7&8 DAC sample rates set to “BB80h” (48kHz)

• Register 3Ah, field SPSR[1,0] controlling S/PDIF sample rate set to “10” (48kHz)

• Register 2Ah, field SPSA[1,0] controlling S/PDIF AC-link slot assignment set to “10” (slots 6&9)

This requirement ensures that dual Codec (2-ch + 2-ch w/ SPDIF) configurations can support 4-ch OS mixer 48 kHz

PCM output while transmitting 48 kHz independent S/PDIF source output.

5.10.1.4 Primary or Secondary codec supports independent S/PDIF transmission of PCM or encoded stream

on slots 10&11

Any Primary or Secondary Codec which supports S/PDIF must accept 48kHz PCM or encoded multichannel data on

AC-Link slots 10&11 for concurrent S/PDIF transmission. SPCV must indicate valid configuration when

programmed as follows:

• Register 3Ah, field SPSR[1,0] controlling S/PDIF sample rate set to “10” (48kHz)

• Register 2Ah, field SPSA[1,0] controlling S/PDIF AC-link slot assignment set to “11” (slots 10&11)

This requirement ensures that codecs supporting S/PDIF will always be able to support an independent S/PDIF

stream transmitted on slots 10&11, without regard to the bit depth, sample rate, or number of channels being

transmitted on the PCM stream which may occupy any of slots 3&4, 7&8, and 6&9.

5.10.2 Optional support for rates other than 48 kHz

The following section describes support for two optional features for non 48 kHz AC-link data: upsampling

capability and “bit exact” transmission. Support for these options requires unambiguous specification of all sample

rates involved:

1. the mixed PCM data rate on slots 3&4 — controlled by the DAC sample rate Register 2Ch

the pass-thru data rate on slots 7&8, 6&9, or 10&11 — restricted to rates that match the SPSR setting

the S/PDIF transmission rate — controlled by the SPSR field

In the following optional non 48 kHz scenarios the SPCV bit becomes essential to identifying the capability.

5.10.2.1 Simultaneous DAC playback and S/PDIF transmission of a single 2-ch non 48 kHz PCM stream

S/PDIF capable Codec provides SRC capability to accept non 48 kHz PCM data on AC-link slots 3&4 and up-

sample to 48 kHz for concurrent DA conversion at 48 kHz and S/PDIF transmission at 48kHz. If supported, SPCV

should indicate valid configuration when programmed as follows:

• VRA mode enabled

• Register 2Ch controlling AC-link slots 3&4 DAC sample rates set to “xxxxh” (8-48kHz)

• Register 3Ah, field SPSR[1,0] controlling S/PDIF sample rate set to “10” (48kHz)

• Register 2Ah, field SPSA[1,0] controlling S/PDIF slot assignment set to “00” (slots 3&4)

This option extends the basic support for OS mixer to 8-48 kHz PCM output to DAC and S/PDIF transmitter.

5.10.2.2 Simultaneous DAC playback and S/PDIF transmission of “bit exact” 32, 44.1, or 48 kHz PCM

streams

S/PDIF capable Codec provides an output S/PDIF rate which tracks the sample rate for Fs = 32, 44.1 or 48.0 kHz.

The S/PDIF transmitter output symbol rate will be 64*Fs as defined by IEC958. In this scenario the S/PDIF

transmitter will be running at the same rate as the incoming PCM stream requiring no SRC in the Codec. This

allows the Codec to simply pass the PCM data from the source to the destination without sample rate conversion,