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linux音訊子系統 - DAPM

阿新 • • 發佈：2018-11-03

Dynamic Audio Power Management for Portable Devices
移動裝置的動態電源管理(DAPM)

1. Description

DAPM使得使用音訊子系統的移動linux裝置，在任何時候，都能夠獲得最小功耗。DAPM獨立於
kernel中其他PM系統，能夠和其他PM系統和諧共存。

DAPM對於使用者層是透明的，電源切換在asoc-driver層完成。使用者層的程式碼不需要改變重編。
DAPM做出電源切換的決定基於音訊流的活動狀態和mixer裝置的配置狀態。

DAPM橫跨整個machine，它覆蓋整個音訊子系統的電源控制，包括codec電源塊和machine層的電源系統。

DAPM有四個主要的電源域:

  • 1.codec電源域 - VREF,VMID(core codec和audio power)
    此域通常由probe/remove和suspend/resume來控制。
  • 2.platform/machine域 - 輸入輸出物理連線
    這部分是platform/machine和使用者自定義來配置
  • 3.path域 - audio子系統訊號路徑
    使用者層改變mixer和mux配置時自動設定
  • 4.stream域 - DAC和ADC
    當播放和錄音開始結束時，使能和關閉

所有DAPM的電源控制由整個machine的音訊鏈路(routing map)來決定，整個鏈路對於每個machine來說都是特定的，
它由每個音訊單元的連線組成，所有影響功耗的音訊單元我們稱為widget(小部件)。

2. DAPM小部件

所有DAPM widget不外乎下面幾種型別：

o Mixer - Mixes several analog signals into a single analog signal.
o Mux - An analog switch that outputs only one of many inputs.
o PGA - A programmable gain amplifier or attenuation widget.
o ADC - Analog to Digital Converter
o DAC - Digital to Analog Converter
o Switch - An analog switch
o Input - A codec input pin
o Output - A codec output pin
o Headphone - Headphone (and optional Jack)
o Mic - Mic (and optional Jack)
o Line - Line Input/Output (and optional Jack)
o Speaker - Speaker
o Supply - Power or clock supply widget used by other widgets.
o Pre - Special PRE widget (exec before all others)
o Post - Special POST widget (exec after all others)

(Widgets are defined in include/sound/soc-dapm.h)

widget通常在codec和machine驅動中增加，在檔案soc-dapm.h檔案中有許多巨集定義可以方便快速的定義
codec widget 和 machine DAPM widget。

大部分widget有name, register, shift and invert欄位，還有的widget有額外的元素，包括
stream name和kcontrol。

2.1 stream域的部件

stream的部件和stream電源域相關，只包含ADC和DAC兩種部件

Stream widgets have the following format:-

SND_SOC_DAPM_DAC(name, stream name, reg, shift, invert),

NOTE: stream name必須匹配snd_soc_codec_dai的name

e.g. stream widgets for HiFi playback and capture

SND_SOC_DAPM_DAC("HiFi DAC", "HiFi Playback", REG, 3, 1),
SND_SOC_DAPM_ADC("HiFi ADC", "HiFi Capture", REG, 2, 1),

2.2 path域的部件

path域的部件主要是控制和影響audio子系統中的audio signal或者audio path，它們用下面的形式來表示：

SND_SOC_DAPM_PGA(name, reg, shift, invert, controls, num_controls)

任何部件的kcontrol裝置可以由controls和num_controls成員來設定

e.g. Mixer widget (the kcontrols are declared first)

/* Output Mixer */
static const snd_kcontrol_new_t wm8731_output_mixer_controls[] = {
SOC_DAPM_SINGLE("Line Bypass Switch", WM8731_APANA, 3, 1, 0),
SOC_DAPM_SINGLE("Mic Sidetone Switch", WM8731_APANA, 5, 1, 0),
SOC_DAPM_SINGLE("HiFi Playback Switch", WM8731_APANA, 4, 1, 0),
};

SND_SOC_DAPM_MIXER("Output Mixer", WM8731_PWR, 4, 1, wm8731_output_mixer_controls,
    ARRAY_SIZE(wm8731_output_mixer_controls)),

如果你不想在mixer元素前面加上mixer部件的字首，那麼可以使用SND_SOC_DAPM_MIXER_NAMED_CTL來替代，
這個定義和SND_SOC_DAPM_MIXER是一樣的

2.3 platform/machine域部件

machine部件和codec部件不一樣，它們沒有相關的codec暫存器，一個machine部件就是一個audio單元，
可以獨立供電，比如下面的器件:

o Speaker Amp
o Microphone Bias
o Jack connectors

一個machine部件有一個可選的呼叫函式

舉例：當麥克風插入時，外部的麥克風介面部件需要使能偏壓：
static int spitz_mic_bias(struct snd_soc_dapm_widget* w, int event)
{
    gpio_set_value(SPITZ_GPIO_MIC_BIAS, SND_SOC_DAPM_EVENT_ON(event));
    return 0;
}

SND_SOC_DAPM_MIC("Mic Jack", spitz_mic_bias),

2.4 codec域

codec電源域沒有部件，它由codec DAPM event來操作.event的操作發生在codec電源狀態改變的時候，
或者通過kernel PM事件來觸發

2.5 虛擬部件

有時codec和machine中的部件沒有相關電源控制的操作，對於此種情況，就需要建立一個虛擬的部件，如下

SND_SOC_DAPM_MIXER("AC97 Mixer", SND_SOC_DAPM_NOPM, 0, 0, NULL, 0),

這個可以在軟體層面單獨和入到一個訊號路徑上

所有的部件都定義好後，它們就可以加入到DAPM子系統中，通過介面snd_soc_dapm_new_control分別呼叫

3. codec部件相互連線

codec和machine的widget通過audio path來建立相互連線，每個連線必須按順序通過
建立部件之間的path對映來定義

這個很容易建立一個codec的圖表，它需要把經過audio signal路徑的部件一起加入進來

以wm8731輸出混合器為例：

The WM8731 output mixer has 3 inputs (sources)

  1. Line Bypass Input
  2. DAC (HiFi playback)
  3. Mic Sidetone Input

Each input in this example has a kcontrol associated with it (defined in example
above) and is connected to the output mixer via its kcontrol name. We can now
connect the destination widget (wrt audio signal) with its source widgets.

/* output mixer */
{"Output Mixer", "Line Bypass Switch", "Line Input"},
{"Output Mixer", "HiFi Playback Switch", "DAC"},
{"Output Mixer", "Mic Sidetone Switch", "Mic Bias"},

So we have :-

Destination Widget  <=== Path Name <=== Source Widget

Or:-

Sink, Path, Source

Or :-

"Output Mixer" is connected to the "DAC" via the "HiFi Playback Switch".

當相互連線的部件沒有path name時，我們用NULL來表示

連線的建立通過呼叫下面的函式：

snd_soc_dapm_connect_input(codec, sink, path, source);

最終，在所有的部件和連線都註冊到系統後，snd_soc_dapm_new_widgets(codec)必須被呼叫，這樣會導致
系統去掃描codec和machine，以便DAPM狀態可以匹配到machine的物理狀態

3.1 machine部件連線

machine部件的連線建立過程和codec一樣，直接連線codec到machine層部件

舉例：連線speaker輸出codec引腳到內部的speaker

/* ext speaker connected to codec pins LOUT2, ROUT2  */
{"Ext Spk", NULL , "ROUT2"},
{"Ext Spk", NULL , "LOUT2"},

這樣會允許DAPM對有連線的引腳和未使用的引腳來上下電

4. 端點部件

一個端點是machine包括codec音訊訊號的開始或者結束，包括以下幾個:

  • o Headphone Jack
  • o Internal Speaker
  • o Internal Mic
  • o Mic Jack
  • o Codec Pins

當一個codec的引腳是NC時，它可以被標誌為未使用，可以用下面函式來設定

snd_soc_dapm_set_endpoint(codec, "Widget Name", 0);

最後的引數0代表未活動狀態，1代表活動狀態，通過這種方式可以讓某些部件永遠不會上電，從而節省功耗

這個也適用於machine部件，比如，一個耳機連線到一個插孔，那麼這個插孔需要被標誌為活動的，如果一個
耳機被拔出，那麼這個耳機插孔需要被標誌為未活動的

5. DAPM部件事件機制

一些部件可以註冊它們感興趣的到系統的PM事件中，比如，一個帶了放大器的揚聲器註冊為一個部件，
那麼這個放大器部件只會在揚聲器使用的時候上電

/* turn speaker amplifier on/off depending on use */
static int corgi_amp_event(struct snd_soc_dapm_widget *w, int event)
{
    gpio_set_value(CORGI_GPIO_APM_ON, SND_SOC_DAPM_EVENT_ON(event));
    return 0;
}

/* corgi machine dapm widgets */
static const struct snd_soc_dapm_widget wm8731_dapm_widgets =
    SND_SOC_DAPM_SPK("Ext Spk", corgi_amp_event);

對於所有支援事件的部件請看檔案soc-dapm.h

5.1 事件型別

部件支援下面幾種事件型別
/* dapm event types */
#define SND_SOC_DAPM_PRE_PMU 0x1 /* before widget power up */
#define SND_SOC_DAPM_POST_PMU 0x2 /* after widget power up */
#define SND_SOC_DAPM_PRE_PMD 0x4 /* before widget power down */
#define SND_SOC_DAPM_POST_PMD 0x8 /* after widget power down */
#define SND_SOC_DAPM_PRE_REG 0x10 /* before audio path setup */
#define SND_SOC_DAPM_POST_REG 0x20 /* after audio path setup */

附錄

Dynamic Audio Power Management for Portable Devices

1. Description

Dynamic Audio Power Management (DAPM) is designed to allow portable
Linux devices to use the minimum amount of power within the audio
subsystem at all times. It is independent of other kernel PM and as
such, can easily co-exist with the other PM systems.

DAPM is also completely transparent to all user space applications as
all power switching is done within the ASoC core. No code changes or
recompiling are required for user space applications. DAPM makes power
switching decisions based upon any audio stream (capture/playback)
activity and audio mixer settings within the device.

DAPM spans the whole machine. It covers power control within the entire
audio subsystem, this includes internal codec power blocks and machine
level power systems.

There are 4 power domains within DAPM

  1. Codec domain - VREF, VMID (core codec and audio power)
    Usually controlled at codec probe/remove and suspend/resume, although
    can be set at stream time if power is not needed for sidetone, etc.

  2. Platform/Machine domain - physically connected inputs and outputs
    Is platform/machine and user action specific, is configured by the
    machine driver and responds to asynchronous events e.g when HP
    are inserted

  3. Path domain - audio susbsystem signal paths
    Automatically set when mixer and mux settings are changed by the user.
    e.g. alsamixer, amixer.

  4. Stream domain - DACs and ADCs.
    Enabled and disabled when stream playback/capture is started and
    stopped respectively. e.g. aplay, arecord.

All DAPM power switching decisions are made automatically by consulting an audio
routing map of the whole machine. This map is specific to each machine and
consists of the interconnections between every audio component (including
internal codec components). All audio components that effect power are called
widgets hereafter.

2. DAPM Widgets

Audio DAPM widgets fall into a number of types:-

o Mixer - Mixes several analog signals into a single analog signal.
o Mux - An analog switch that outputs only one of many inputs.
o PGA - A programmable gain amplifier or attenuation widget.
o ADC - Analog to Digital Converter
o DAC - Digital to Analog Converter
o Switch - An analog switch
o Input - A codec input pin
o Output - A codec output pin
o Headphone - Headphone (and optional Jack)
o Mic - Mic (and optional Jack)
o Line - Line Input/Output (and optional Jack)
o Speaker - Speaker
o Supply - Power or clock supply widget used by other widgets.
o Pre - Special PRE widget (exec before all others)
o Post - Special POST widget (exec after all others)

(Widgets are defined in include/sound/soc-dapm.h)

Widgets are usually added in the codec driver and the machine driver. There are
convenience macros defined in soc-dapm.h that can be used to quickly build a
list of widgets of the codecs and machines DAPM widgets.

Most widgets have a name, register, shift and invert. Some widgets have extra
parameters for stream name and kcontrols.

2.1 Stream Domain Widgets

Stream Widgets relate to the stream power domain and only consist of ADCs
(analog to digital converters) and DACs (digital to analog converters).

Stream widgets have the following format:-

SND_SOC_DAPM_DAC(name, stream name, reg, shift, invert),

NOTE: the stream name must match the corresponding stream name in your codec
snd_soc_codec_dai.

e.g. stream widgets for HiFi playback and capture

SND_SOC_DAPM_DAC(“HiFi DAC”, “HiFi Playback”, REG, 3, 1),
SND_SOC_DAPM_ADC(“HiFi ADC”, “HiFi Capture”, REG, 2, 1),

2.2 Path Domain Widgets

Path domain widgets have a ability to control or affect the audio signal or
audio paths within the audio subsystem. They have the following form:-

SND_SOC_DAPM_PGA(name, reg, shift, invert, controls, num_controls)

Any widget kcontrols can be set using the controls and num_controls members.

e.g. Mixer widget (the kcontrols are declared first)

/* Output Mixer */
static const snd_kcontrol_new_t wm8731_output_mixer_controls[] = {
SOC_DAPM_SINGLE(“Line Bypass Switch”, WM8731_APANA, 3, 1, 0),
SOC_DAPM_SINGLE(“Mic Sidetone Switch”, WM8731_APANA, 5, 1, 0),
SOC_DAPM_SINGLE(“HiFi Playback Switch”, WM8731_APANA, 4, 1, 0),
};

SND_SOC_DAPM_MIXER(“Output Mixer”, WM8731_PWR, 4, 1, wm8731_output_mixer_controls,
ARRAY_SIZE(wm8731_output_mixer_controls)),

If you dont want the mixer elements prefixed with the name of the mixer widget,
you can use SND_SOC_DAPM_MIXER_NAMED_CTL instead. the parameters are the same
as for SND_SOC_DAPM_MIXER.

2.3 Platform/Machine domain Widgets

Machine widgets are different from codec widgets in that they don’t have a
codec register bit associated with them. A machine widget is assigned to each
machine audio component (non codec) that can be independently powered. e.g.

o Speaker Amp
o Microphone Bias
o Jack connectors

A machine widget can have an optional call back.

e.g. Jack connector widget for an external Mic that enables Mic Bias
when the Mic is inserted:-

static int spitz_mic_bias(struct snd_soc_dapm_widget* w, int event)
{
gpio_set_value(SPITZ_GPIO_MIC_BIAS, SND_SOC_DAPM_EVENT_ON(event));
return 0;
}

SND_SOC_DAPM_MIC(“Mic Jack”, spitz_mic_bias),

2.4 Codec Domain

The codec power domain has no widgets and is handled by the codecs DAPM event
handler. This handler is called when the codec powerstate is changed wrt to any
stream event or by kernel PM events.

2.5 Virtual Widgets

Sometimes widgets exist in the codec or machine audio map that don’t have any
corresponding soft power control. In this case it is necessary to create
a virtual widget - a widget with no control bits e.g.

SND_SOC_DAPM_MIXER(“AC97 Mixer”, SND_SOC_DAPM_NOPM, 0, 0, NULL, 0),

This can be used to merge to signal paths together in software.

After all the widgets have been defined, they can then be added to the DAPM
subsystem individually with a call to snd_soc_dapm_new_control().

3. Codec Widget Interconnections

Widgets are connected to each other within the codec and machine by audio paths
(called interconnections). Each interconnection must be defined in order to
create a map of all audio paths between widgets.

This is easiest with a diagram of the codec (and schematic of the machine audio
system), as it requires joining widgets together via their audio signal paths.

e.g., from the WM8731 output mixer (wm8731.c)

The WM8731 output mixer has 3 inputs (sources)

  1. Line Bypass Input
  2. DAC (HiFi playback)
  3. Mic Sidetone Input

Each input in this example has a kcontrol associated with it (defined in example
above) and is connected to the output mixer via its kcontrol name. We can now
connect the destination widget (wrt audio signal) with its source widgets.

/* output mixer */
{"Output Mixer", "Line Bypass Switch", "Line Input"},
{"Output Mixer", "HiFi Playback Switch", "DAC"},
{"Output Mixer", "Mic Sidetone Switch", "Mic Bias"},

So we have :-

Destination Widget  <=== Path Name <=== Source Widget

Or:-

Sink, Path, Source

Or :-

"Output Mixer" is connected to the "DAC" via the "HiFi Playback Switch".

When there is no path name connecting widgets (e.g. a direct connection) we
pass NULL for the path name.

Interconnections are created with a call to:-

snd_soc_dapm_connect_input(codec, sink, path, source);

Finally, snd_soc_dapm_new_widgets(codec) must be called after all widgets and
interconnections have been registered with the core. This causes the core to
scan the codec and machine so that the internal DAPM state matches the
physical state of the machine.

3.1 Machine Widget Interconnections

Machine widget interconnections are created in the same way as codec ones and
directly connect the codec pins to machine level widgets.

e.g. connects the speaker out codec pins to the internal speaker.

/* ext speaker connected to codec pins LOUT2, ROUT2  */
{"Ext Spk", NULL , "ROUT2"},
{"Ext Spk", NULL , "LOUT2"},

This allows the DAPM to power on and off pins that are connected (and in use)
and pins that are NC respectively.

4 Endpoint Widgets

An endpoint is a start or end point (widget) of an audio signal within the
machine and includes the codec. e.g.

o Headphone Jack
o Internal Speaker
o Internal Mic
o Mic Jack
o Codec Pins

When a codec pin is NC it can be marked as not used with a call to

snd_soc_dapm_set_endpoint(codec, “Widget Name”, 0);

The last argument is 0 for inactive and 1 for active. This way the pin and its
input widget will never be powered up and consume power.

This also applies to machine widgets. e.g. if a headphone is connected to a
jack then the jack can be marked active. If the headphone is removed, then
the headphone jack can be marked inactive.

5 DAPM Widget Events

Some widgets can register their interest with the DAPM core in PM events.
e.g. A Speaker with an amplifier registers a widget so the amplifier can be
powered only when the spk is in use.

/* turn speaker amplifier on/off depending on use */
static int corgi_amp_event(struct snd_soc_dapm_widget *w, int event)
{
gpio_set_value(CORGI_GPIO_APM_ON, SND_SOC_DAPM_EVENT_ON(event));
return 0;
}

/* corgi machine dapm widgets */
static const struct snd_soc_dapm_widget wm8731_dapm_widgets =
SND_SOC_DAPM_SPK(“Ext Spk”, corgi_amp_event);

Please see soc-dapm.h for all other widgets that support events.

5.1 Event types

The following event types are supported by event widgets.

/* dapm event types */
#define SND_SOC_DAPM_PRE_PMU 0x1 /* before widget power up */
#define SND_SOC_DAPM_POST_PMU 0x2 /* after widget power up */
#define SND_SOC_DAPM_PRE_PMD 0x4 /* before widget power down */
#define SND_SOC_DAPM_POST_PMD 0x8 /* after widget power down */
#define SND_SOC_DAPM_PRE_REG 0x10 /* before audio path setup */
#define SND_SOC_DAPM_POST_REG 0x20 /* after audio path setup */

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