[mirror_ubuntu-bionic-kernel.git] / Documentation / sound / soc / dai.rst

==================================
ASoC Digital Audio Interface (DAI)
==================================

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
====

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 :
http://www.intel.com/p/en_US/business/design


I2S
===

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:-

I2S
  MSB is transmitted on the falling edge of the first BCLK after LRC
  transition.

Left Justified
  MSB is transmitted on transition of LRC.

Right Justified
  MSB is transmitted sample size BCLKs before LRC transition.

PCM
===

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:-

Mode A
  MSB is transmitted on falling edge of first BCLK after FRAME/SYNC.

Mode B
  MSB is transmitted on rising edge of FRAME/SYNC.
Commit	Line	Data
e732d1bc TI	1	==================================
	2	ASoC Digital Audio Interface (DAI)
	3	==================================
	4
eb1a6af3	5	ASoC currently supports the three main Digital Audio Interfaces (DAI) found on
7c4dbbd8	6	SoC controllers and portable audio CODECs today, namely AC97, I2S and PCM.
eb1a6af3 LG	7
	8
	9	AC97
	10	====
	11
e732d1bc	12	AC97 is a five wire interface commonly found on many PC sound cards. It is
eb1a6af3 LG	13	now also popular in many portable devices. This DAI has a reset line and time
	14	multiplexes its data on its SDATA_OUT (playback) and SDATA_IN (capture) lines.
	15	The bit clock (BCLK) is always driven by the CODEC (usually 12.288MHz) and the
	16	frame (FRAME) (usually 48kHz) is always driven by the controller. Each AC97
	17	frame is 21uS long and is divided into 13 time slots.
	18
e732d1bc	19	The AC97 specification can be found at :
0ea6e611	20	http://www.intel.com/p/en_US/business/design
eb1a6af3 LG	21
	22
	23	I2S
	24	===
	25
e732d1bc	26	I2S is a common 4 wire DAI used in HiFi, STB and portable devices. The Tx and
01dd2fbf	27	Rx lines are used for audio transmission, whilst the bit clock (BCLK) and
eb1a6af3 LG	28	left/right clock (LRC) synchronise the link. I2S is flexible in that either the
	29	controller or CODEC can drive (master) the BCLK and LRC clock lines. Bit clock
	30	usually 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
7c4dbbd8	32	ADC and DAC LRCLKs, this allows for simultaneous capture and playback at
eb1a6af3 LG	33	different sample rates.
	34
	35	I2S has several different operating modes:-
	36
e732d1bc TI	37	I2S
	38	MSB is transmitted on the falling edge of the first BCLK after LRC
	39	transition.
eb1a6af3	40
e732d1bc TI	41	Left Justified
e732d1bc TI	42	MSB is transmitted on transition of LRC.
eb1a6af3	43
e732d1bc TI	44	Right Justified
e732d1bc TI	45	MSB is transmitted sample size BCLKs before LRC transition.
eb1a6af3 LG	46
	47	PCM
	48	===
	49
01dd2fbf	50	PCM is another 4 wire interface, very similar to I2S, which can support a more
eb1a6af3 LG	51	flexible protocol. It has bit clock (BCLK) and sync (SYNC) lines that are used
	52	to synchronise the link whilst the Tx and Rx lines are used to transmit and
	53	receive the audio data. Bit clock usually varies depending on sample rate
	54	whilst sync runs at the sample rate. PCM also supports Time Division
01dd2fbf	55	Multiplexing (TDM) in that several devices can use the bus simultaneously (this
eb1a6af3 LG	56	is sometimes referred to as network mode).
	57
	58	Common PCM operating modes:-
	59
e732d1bc TI	60	Mode A
e732d1bc TI	61	MSB is transmitted on falling edge of first BCLK after FRAME/SYNC.
eb1a6af3	62
e732d1bc TI	63	Mode B
e732d1bc TI	64	MSB is transmitted on rising edge of FRAME/SYNC.