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dai.rst

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  1. ==================================
    2. 

  2. ASoC Digital Audio Interface (DAI)
    3. 

  3. ==================================
    4. 

  4. 

  5. ASoC currently supports the three main Digital Audio Interfaces (DAI) found on
    6. 

  6. SoC controllers and portable audio CODECs today, namely AC97, I2S and PCM.
    7. 

  7. 

  8. 

  9. AC97
    10. 

  10. ====
    11. 

  11. 

  12. AC97 is a five wire interface commonly found on many PC sound cards. It is
    13. 

  13. now also popular in many portable devices. This DAI has a RESET line and time
    14. 

  14. multiplexes its data on its SDATA_OUT (playback) and SDATA_IN (capture) lines.
    15. 

  15. The bit clock (BCLK) is always driven by the CODEC (usually 12.288MHz) and the
    16. 

  16. frame (FRAME) (usually 48kHz) is always driven by the controller. Each AC97
    17. 

  17. frame is 21uS long and is divided into 13 time slots.
    18. 

  18. 

  19. The AC97 specification can be found at :
    20. 

  20. https://www.intel.com/p/en_US/business/design
    21. 

  21. 

  22. 

  23. I2S
    24. 

  24. ===
    25. 

  25. 

  26. I2S is a common 4 wire DAI used in HiFi, STB and portable devices. The Tx and
    27. 

  27. Rx lines are used for audio transmission, while the bit clock (BCLK) and
    28. 

  28. left/right clock (LRC) synchronise the link. I2S is flexible in that either the
    29. 

  29. controller or CODEC can drive (master) the BCLK and LRC clock lines. Bit clock
    30. 

  30. usually varies depending on the sample rate and the master system clock
    31. 

  31. (SYSCLK). LRCLK is the same as the sample rate. A few devices support separate
    32. 

  32. ADC and DAC LRCLKs, this allows for simultaneous capture and playback at
    33. 

  33. different sample rates.
    34. 

  34. 

  35. I2S has several different operating modes:-
    36. 

  36. 

  37. I2S
    38. 

  38.   MSB is transmitted on the falling edge of the first BCLK after LRC
    39. 

  39.   transition.
    40. 

  40. 

  41. Left Justified
    42. 

  42.   MSB is transmitted on transition of LRC.
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  43. 

  44. Right Justified
    45. 

  45.   MSB is transmitted sample size BCLKs before LRC transition.
    46. 

  46. 

  47. PCM
    48. 

  48. ===
    49. 

  49. 

  50. PCM is another 4 wire interface, very similar to I2S, which can support a more
    51. 

  51. flexible protocol. It has bit clock (BCLK) and sync (SYNC) lines that are used
    52. 

  52. to synchronise the link while the Tx and Rx lines are used to transmit and
    53. 

  53. receive the audio data. Bit clock usually varies depending on sample rate
    54. 

  54. while sync runs at the sample rate. PCM also supports Time Division
    55. 

  55. Multiplexing (TDM) in that several devices can use the bus simultaneously (this
    56. 

  56. is sometimes referred to as network mode).
    57. 

  57. 

  58. Common PCM operating modes:-
    59. 

  59. 

  60. Mode A
    61. 

  61.   MSB is transmitted on falling edge of first BCLK after FRAME/SYNC.
    62. 

  62. 

  63. Mode B
    64. 

  64.   MSB is transmitted on rising edge of FRAME/SYNC.
    65.