1==================================
2ASoC Digital Audio Interface (DAI)
3==================================
4
5ASoC currently supports the three main Digital Audio Interfaces (DAI) found on
6SoC controllers and portable audio CODECs today, namely AC97, I2S and PCM.
7
8
9AC97
10====
11
12AC97 is a five wire interface commonly found on many PC sound cards. It is
13now also popular in many portable devices. This DAI has a reset line and time
14multiplexes its data on its SDATA_OUT (playback) and SDATA_IN (capture) lines.
15The bit clock (BCLK) is always driven by the CODEC (usually 12.288MHz) and the
16frame (FRAME) (usually 48kHz) is always driven by the controller. Each AC97
17frame is 21uS long and is divided into 13 time slots.
18
19The AC97 specification can be found at :
20https://www.intel.com/p/en_US/business/design
21
22
23I2S
24===
25
26I2S is a common 4 wire DAI used in HiFi, STB and portable devices. The Tx and
27Rx lines are used for audio transmission, while the bit clock (BCLK) and
28left/right clock (LRC) synchronise the link. I2S is flexible in that either the
29controller or CODEC can drive (master) the BCLK and LRC clock lines. Bit clock
30usually varies depending on the sample rate and the master system clock
31(SYSCLK). LRCLK is the same as the sample rate. A few devices support separate
32ADC and DAC LRCLKs, this allows for simultaneous capture and playback at
33different sample rates.
34
35I2S has several different operating modes:-
36
37I2S
38  MSB is transmitted on the falling edge of the first BCLK after LRC
39  transition.
40
41Left Justified
42  MSB is transmitted on transition of LRC.
43
44Right Justified
45  MSB is transmitted sample size BCLKs before LRC transition.
46
47PCM
48===
49
50PCM is another 4 wire interface, very similar to I2S, which can support a more
51flexible protocol. It has bit clock (BCLK) and sync (SYNC) lines that are used
52to synchronise the link while the Tx and Rx lines are used to transmit and
53receive the audio data. Bit clock usually varies depending on sample rate
54while sync runs at the sample rate. PCM also supports Time Division
55Multiplexing (TDM) in that several devices can use the bus simultaneously (this
56is sometimes referred to as network mode).
57
58Common PCM operating modes:-
59
60Mode A
61  MSB is transmitted on falling edge of first BCLK after FRAME/SYNC.
62
63Mode B
64  MSB is transmitted on rising edge of FRAME/SYNC.
65