alc268 Realtek Semiconductor Corporation, alc268 Datasheet - Page 25

• Manufacturer Part Number: alc268
• Description: 2+2 Channel High Definition Audio Codec
• Manufacturer: Realtek Semiconductor Corporation

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 onto 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 18, 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 18, 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.
2+2 Channel High Definition Audio Codec
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 13. 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
17
Stream 'X'
0s
Track ID: JATR-1076-21
Stream 'Y'
ALC268 Series
0s
Datasheet
Rev. 1.3