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The audio class provides several structures that can be used to build an audio function topology. These structures relate to units, terminals and streams. They will be declared and initialized in usbd_audio_dev_cfg.h and usbd_audio_dev_cfg.c files. Table - User Configurable Structures for Creating Audio Function Topology presents all configurable structures and the associated function that will use the structure. Functions are described in Class Instance Configuration section.

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title	Table - User Configurable Structures for Creating Audio Function Topology

Structure	Description	Associated Function
`USBD_AUDIO_IT_CFG`	Configures an Input terminal.	`USBD_Audio_IT_Add()`
`USBD_AUDIO_OT_CFG`	Configures an Output terminal.	`USBD_Audio_OT_Add()`
`USBD_AUDIO_FU_CFG`	Configures a Feature Unit.	`USBD_Audio_FU_Add()`
`USBD_AUDIO_MU_CFG`	Configures a Mixer Unit.	`USBD_Audio_MU_Add()`
`USBD_AUDIO_SU_CFG`	Configures a Selector Unit.	`USBD_Audio_SU_Add()`
`USBD_AUDIO_AS_ALT_CFG`	Configures an operational AudioStreaming interface.	`USBD_Audio_AS_IF_Cfg()`
`USBD_AUDIO_AS_IF_CFG`	Gathers information about all alternate settings configuration for a given AudioStreaming interface.	`USBD_Audio_AS_IF_Add() USBD_Audio_AS_IF_Cfg()`
`USBD_AUDIO_STREAM_CFG`	Configures stream in terms of buffers and built-in stream correction.	`USBD_Audio_AS_IF_Cfg()`

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Two Inputs terminals
Two Ouput terminals
Two Feature units
Two AudioStreaming interfaces

Figure - usbd_audio_dev_cfg.c - Typical Topologies Example gives a visual representation of the possible topologies that can be built with the 6 terminals and units.

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Info
All terminals must have a unique ID within a given audio function. The terminals ID assignment is handled by the audio class using the functions `USBD_Audio_IT_Assoc` and `USBD_Audio_OT_Assoc` .

Input Terminal

Table - USBD_AUDIO_IT_CFG Structure Fields Description presents the Input terminal structure. Refer to audio 1.0 specification, section "4.3.2.1 Input Terminal Descriptor" for more details about certain fields.

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title	Table - USBD_AUDIO_IT_CFG Structure Fields Description

Field	Description	Example of value	Available Predefined Value
`TerminalType`	Terminal type.	`USBD_AUDIO_TERMINAL_TYPE_MIC`	There are many terminal type defined by Audio 1.0 Terminal Types specification. Thus, there are many predefined values available in `usbd_audio.h`. Some of them typical for IT are: `USBD_AUDIO_TERMINAL_TYPE_USB_STREAMING USBD_AUDIO_TERMINAL_TYPE_IT_UNDEFINED USBD_AUDIO_TERMINAL_TYPE_MIC USBD_AUDIO_TERMINAL_TYPE_DESKTOP_MIC USBD_AUDIO_TERMINAL_TYPE_OMNI_DIR_MIC USBD_AUDIO_TERMINAL_TYPE_PERSONAL_MIC USBD_AUDIO_TERMINAL_TYPE_MIC_ARRAY USBD_AUDIO_TERMINAL_TYPE_PROC_MIC_ARRAY` Refer to `usbd_audio.h` for the complete list.
`LogChNbr`	Number of logical output channels in the terminal output.	`USBD_AUDIO_MONO`	`USBD_AUDIO_MONO` `USBD_AUDIO_STEREO` `USBD_AUDIO_5_1` `USBD_AUDIO_7_1`
`LogChCfg`	Spatial location of logical channel.	`USBD_AUDIO_SPATIAL_LOCATION_LEFT_FRONT`	A `OR` combination of: `USBD_AUDIO_SPATIAL_LOCATION_LEFT_FRONT` `USBD_AUDIO_SPATIAL_LOCATION_RIGHT_FRONT` `USBD_AUDIO_SPATIAL_LOCATION_CENTER_FRONT` `USBD_AUDIO_SPATIAL_LOCATION_LFE` `USBD_AUDIO_SPATIAL_LOCATION_LEFT_SURROUND` `USBD_AUDIO_SPATIAL_LOCATION_RIGHT_SURROUND` `USBD_AUDIO_SPATIAL_LOCATION_LEFT_CENTER` `USBD_AUDIO_SPATIAL_LOCATION_RIGHT_CENTER` `USBD_AUDIO_SPATIAL_LOCATION_SURROUND` `USBD_AUDIO_SPATIAL_LOCATION_SIDE_LEFT` `USBD_AUDIO_SPATIAL_LOCATION_SIDE_RIGHT` `USBD_AUDIO_SPATIAL_LOCATION_TOP`
`CopyProtEn`	Enables or disables Copy Protection.	`DEF_DISABLED`	`DEF_DISABLED` `DEF_ENABLED`
`CopyProtLevel`	Copy Protection Level.	`USBD_AUDIO_CPL_NONE`	`USBD_AUDIO_CPL_NONE` `USBD_AUDIO_CPL0` `USBD_AUDIO_CPL1` `USBD_AUDIO_CPL2`
`StrPtr`	Pointer to a string describing the Input Terminal.	"IT Microphone"	-

Output Terminal

Table - USBD_AUDIO_OT_CFG Structure Fields Description presents the Output terminal structure. Refer to audio 1.0 specification, section "4.3.2.2 Output Terminal Descriptor" for more details about certain fields.

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Info
All units must have a unique ID within a given audio function. The units ID assignment is handled by the audio class using the functions `USBD_Audio_FU_Assoc` , USBD_Audio_MU_Assoc() and USBD_Audio_SU_Assoc.

Feature Unit

Table - USBD_AUDIO_FU_CFG Structure Fields Description presents the Feature Unit structure. Refer to audio 1.0 specification, section "4.3.2.5 Feature Unit Descriptor" for more details about certain fields.

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Info
A Mixer Unit can have programmable and non-programmable mixing controls. If you need to set some programmable mixing controls, you need to use the function `USBD_Audio_MU_MixingCtrlSet` during the audio function initialization.

Selector Unit

Table - USBD_AUDIO_SU_CFG Structure Fields Description 106037317 presents the Selector Unit structure. Refer to audio 1.0 specification, section "4.3.2.4 Selector Unit Descriptor" for more details about certain fields.

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General Stream Configuration

Table - USBD_AUDIO_STREAM_CFG Structure Fields Description presents the general stream configuration structure.

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title	Table - USBD_AUDIO_STREAM_CFG Structure Fields Description

Field	Description	Example of value	Available Predefined Value
`MaxBufNbr`	Maximum number of buffers allocated for the given stream.	40	`USBD_AUDIO_STREAM_NBR_BUF_6 USBD_AUDIO_STREAM_NBR_BUF_12 USBD_AUDIO_STREAM_NBR_BUF_18 USBD_AUDIO_STREAM_NBR_BUF_24 USBD_AUDIO_STREAM_NBR_BUF_30 USBD_AUDIO_STREAM_NBR_BUF_36 USBD_AUDIO_STREAM_NBR_BUF_42`
`CorrPeriodMs`	Period at which the built-in stream correction must be possibly applied. Expressed in milliseconds. For this field and the two followings, refer to section Stream Correction for more details about the built-in correction for playback and record streams.	2	-

AudioStreaming Interface

Table - USBD_AUDIO_AS_ALT_CFG Structure Fields Description 106037317 presents the AudioStreaming interface configuration structure. Each AudioStreaming interface has one unique associated isochronous endpoint. Hence, there is a one-to-one relation between an AudioStreaming interface and its associated endpoint.

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Code Block

language	cpp
linenumbers	true

CPU_INT32U  AS_SamFreqTbl[] = {
    USBD_AUDIO_FMT_TYPE_I_SAMFREQ_44_1KHZ,
    USBD_AUDIO_FMT_TYPE_I_SAMFREQ_48KHZ
};

Table - USBD_AUDIO_AS_IF_CFG Structure Fields Description 106037317 presents the structure used to gather information about all alternate settings configuration for a given AudioStreaming interface.

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title	Table - USBD_AUDIO_AS_IF_CFG Structure Fields Description

Field	Description	Example of value
`AS_CfgPtrTbl`	Table of pointers to USBD_AUDIO_AS_ALT_CFG structure. Refer to Table - USBD_AUDIO_AS_ALT_CFG Structure Fields Description 106037317 for more details about USBD_AUDIO_AS_ALT_CFG structure.	`&USBD_AS_IF1_Alt_SpeakerCfgTbl[0u],`
`AS_CfgAltSettingNbr`	Nbr of alternate settings for given AS IF	3

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Versions Compared

Old Version 4

New Version Current

Key

Input Terminal

Output Terminal

Feature Unit

Selector Unit

General Stream Configuration

AudioStreaming Interface