Based on kernel version 3.19. Page generated on 2015-02-13 21:22 EST.
1 ASoC currently supports the three main Digital Audio Interfaces (DAI) found on 2 SoC controllers and portable audio CODECs today, namely AC97, I2S and PCM. 3 4 5 AC97 6 ==== 7 8 AC97 is a five wire interface commonly found on many PC sound cards. It is 9 now also popular in many portable devices. This DAI has a reset line and time 10 multiplexes its data on its SDATA_OUT (playback) and SDATA_IN (capture) lines. 11 The bit clock (BCLK) is always driven by the CODEC (usually 12.288MHz) and the 12 frame (FRAME) (usually 48kHz) is always driven by the controller. Each AC97 13 frame is 21uS long and is divided into 13 time slots. 14 15 The AC97 specification can be found at :- 16 http://www.intel.com/p/en_US/business/design 17 18 19 I2S 20 === 21 22 I2S is a common 4 wire DAI used in HiFi, STB and portable devices. The Tx and 23 Rx lines are used for audio transmission, whilst the bit clock (BCLK) and 24 left/right clock (LRC) synchronise the link. I2S is flexible in that either the 25 controller or CODEC can drive (master) the BCLK and LRC clock lines. Bit clock 26 usually 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 28 ADC and DAC LRCLKs, this allows for simultaneous capture and playback at 29 different sample rates. 30 31 I2S 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 41 PCM 42 === 43 44 PCM is another 4 wire interface, very similar to I2S, which can support a more 45 flexible protocol. It has bit clock (BCLK) and sync (SYNC) lines that are used 46 to synchronise the link whilst the Tx and Rx lines are used to transmit and 47 receive the audio data. Bit clock usually varies depending on sample rate 48 whilst sync runs at the sample rate. PCM also supports Time Division 49 Multiplexing (TDM) in that several devices can use the bus simultaneously (this 50 is sometimes referred to as network mode). 51 52 Common 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.