alc885-gr Realtek Semiconductor Corporation, alc885-gr Datasheet - Page 23

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alc885-gr

Manufacturer Part Number
alc885-gr
Description
7.1+2 Channel High-performance Hda Codec With Content Protection
Manufacturer
Realtek Semiconductor Corporation
Datasheet

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7.2.4.
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.
7.2.5.
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 7, page 16, 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 8, page 16, 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. The cadence
“12-11-11-12-11-11-12-11-11-12-11-11-11- (repeat)”
interleaves 13 frames containing no sample blocks in every 160 frames. It provides a low long-term
frequency drift for 44.1kHz of delivery rate. Rates in sub-multiples (1/n) of 44.1kHz also follow this
cadence AND interleave n empty frames. Rates in multiples (n) of 44.1kHz applying this cadence contain
7.1+2 Channel High-Performance HDA Codec
With Content Protection
SYNC
SDI
SDI
Codec drives SDI
0
1
Frame SYNC
Inbound Frame – Multiple SDIs
Variable Sample Rates
Response Stream
Response Stream
0
and SDI
1
Figure 12. Codec Transmits Data Over Multiple SDIs
Tag B
Tag A
Stream A, B, X, and Y are independent and have separate IDs
Stream 'A'
Stream 'B'
Data B
Data A
15
Stream 'X'
0s
Stream 'Y'
ALC885 Series
0s
Datasheet
Rev. 1.1