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