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-ASoC currently supports the three main Digital Audio Interfaces (DAI) found on
-SoC controllers and portable audio CODECs today, namely AC97, I2S and PCM.
- AC97 is a five wire interface commonly found on many PC sound cards. It is
-now also popular in many portable devices. This DAI has a reset line and time
-multiplexes its data on its SDATA_OUT (playback) and SDATA_IN (capture) lines.
-The bit clock (BCLK) is always driven by the CODEC (usually 12.288MHz) and the
-frame (FRAME) (usually 48kHz) is always driven by the controller. Each AC97
-frame is 21uS long and is divided into 13 time slots.
-The AC97 specification can be found at :-
- I2S is a common 4 wire DAI used in HiFi, STB and portable devices. The Tx and
-Rx lines are used for audio transmission, whilst the bit clock (BCLK) and
-left/right clock (LRC) synchronise the link. I2S is flexible in that either the
-controller or CODEC can drive (master) the BCLK and LRC clock lines. Bit clock
-usually varies depending on the sample rate and the master system clock
-(SYSCLK). LRCLK is the same as the sample rate. A few devices support separate
-ADC and DAC LRCLKs, this allows for simultaneous capture and playback at
-different sample rates.
-I2S has several different operating modes:-
- o I2S - MSB is transmitted on the falling edge of the first BCLK after LRC
- transition.
- o Left Justified - MSB is transmitted on transition of LRC.
- o Right Justified - MSB is transmitted sample size BCLKs before LRC
- transition.
-PCM is another 4 wire interface, very similar to I2S, which can support a more
-flexible protocol. It has bit clock (BCLK) and sync (SYNC) lines that are used
-to synchronise the link whilst the Tx and Rx lines are used to transmit and
-receive the audio data. Bit clock usually varies depending on sample rate
-whilst sync runs at the sample rate. PCM also supports Time Division
-Multiplexing (TDM) in that several devices can use the bus simultaneously (this
-is sometimes referred to as network mode).
-Common PCM operating modes:-
- o Mode A - MSB is transmitted on falling edge of first BCLK after FRAME/SYNC.
- o Mode B - MSB is transmitted on rising edge of FRAME/SYNC.