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ALC892

7.1+2 CHANNEL HD AUDIO CODEC WITH CONTENT PROTECTION

Realtek Semiconductor 

ALC892

Datasheet

7.2.4. Inbound Frame – Multiple SDIs

A codec can deliver data to the controller on multiple SDIs to achieve higher bandwidth. If an inbound

stream exceeds the data transfer limits of a single SDI, the codec can divide the data into separate SDI

signals, each of which operate independently, with different stream numbers at the same frame time. This

is similar to having multiple codecs connected to the controller. The controller samples the divided stream

into separate memory with multiple DMA descriptors, then software re-combines the divided data into a

meaningful stream.

SYNC

SDI0

Frame SYNC

Response Stream

Stream 'A'

Tag A Data A

Stream 'X'

Stream 'Y'

Stream 'B'

SDI1

Response Stream Tag B Data B

0s

0s

Codec drives SDI0 and SDI1

Stream A, B, X, and Y are independent and have separate IDs

Figure 12. Codec Transmits Data Over Multiple SDIs

7.2.5. Variable Sample Rates

The HDA link is designed for sample rates of 48kHz. Variable rates of sample are delivered in multiple or

sub-multiple rates of 48kHz. Two sample blocks per frame result in a 96kHz delivery rate, one sample

block over two frames results in a 24kHz delivery rate. The HDA specification states that the sample rate

of the outbound stream be synchronized by the controller, not by the codec. Each stream has its own

sample rate, independent of any other stream.

The HDA controller supports 48kHz and 44.1kHz base rates. Table 4, page 17, shows the recommended

sample rates based on multiples or sub-multiples of one of the two base rates.

Rates in sub-multiples (1/n) of 48kHz are interleaving n frames containing no sample blocks. Rates in

multiples (n) of 48kHz contain n sample blocks in a frame. Table 5, page 17, shows the delivery cadence

of variable rates based on 48kHz.

The HDA link is defined to operate at a fixed 48kHz frame rate. To deliver samples in (sub) multiple

rates of 44.1kHz, an appropriate ratio between 44.1kHz and 48kHz must be maintained to avoid

frequency drift. The appropriate ratio between 44.1kHz and 48kHz is 147/160. Meaning 147 sample

blocks are transmitted every 160 frames.

7.1+2 Channel HD Audio Codec with Content Protection 16

Track ID: JATR-2265-11 Rev. 1.3

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