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 : 20http://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