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