USBAudioConfig Struct Reference

Configuration for USB Audio (inherits sample_rate / channels / bits_per_sample from AudioInfo). More...

#include <USBAudioConfig.h>

Inheritance diagram for USBAudioConfig:

Public Member Functions
virtual void	clear ()
void	copyFrom (AudioInfo info)
	Same as set.
bool	equals (AudioInfo alt)
	Returns true if alt values are the same like the current values.
bool	equalsExSampleRate (AudioInfo alt)
	Checks if only the sample rate is different.
virtual void	logInfo (const char *source="")
	operator bool ()
	Returns true if all components are defined (no component is 0)
bool	operator!= (AudioInfo alt)
	Returns true if alt values are the different from the current values.
bool	operator!= (const USBAudioConfig &other)
bool	operator== (AudioInfo alt)
	Returns true if alt values are the same like the current values.
bool	operator== (const USBAudioConfig &other)
void	set (AudioInfo info)
	Copies the values from info.
void	setAudioInfo (AudioInfo info)
	Same as set.

Public Attributes
bool	begin_usb = false
uint8_t	bits_per_sample = DEFAULT_BITS_PER_SAMPLE
	Number of bits per sample (int16_t = 16 bits)
uint16_t	channels = DEFAULT_CHANNELS
	Number of channels: 2=stereo, 1=mono.
bool	enable_ep_in = true
	device → host (capture / microphone)
bool	enable_ep_in_flow_control = true
bool	enable_ep_out = true
	host → device (playback / speaker)
bool	enable_feedback_ep = true
	Enable isochronous feedback endpoint so the host can adjust its clock.
bool	enable_interrupt_ep = false
bool	enable_multi_sample_rate = false
int16_t	ep_fb = 0x86
	ISO IN (explicit feedback, RX-only mode)
int16_t	ep_in = 0x85
	ISO IN (device → host, capture/microphone)
int16_t	ep_int = 0x87
	INT IN (AC status/change notifications)
int16_t	ep_out = 0x05
	ISO OUT (host → device, playback/speaker)
uint8_t	fifo_packets = 32
uint8_t	itf_num_ac = 0
const char *	manufacturer = "Audio Tools"
uint8_t	max_power_ma = 100
uint16_t	pid = 0x4002
const char *	product = "USB Audio"
sample_rate_t	sample_rate = DEFAULT_SAMPLE_RATE
	Sample Rate: e.g 44100.
bool	self_powered = true
const char *	serial = "000001"
std::vector< uint32_t >	supported_sample_rates
uint8_t	terminal_id = 1
uint16_t	vid = 0xCafe
bool	volume_active = false

Detailed Description

Configuration for USB Audio (inherits sample_rate / channels / bits_per_sample from AudioInfo).

Member Function Documentation

clear()

virtual void clear ( )

inlinevirtualinherited

copyFrom()

void copyFrom ( AudioInfo  info )

inlineinherited

Same as set.

equals()

bool equals ( AudioInfo  alt )

inlineinherited

Returns true if alt values are the same like the current values.

equalsExSampleRate()

bool equalsExSampleRate ( AudioInfo  alt )

inlineinherited

Checks if only the sample rate is different.

logInfo()

virtual void logInfo ( const char *  source = "" )

inlinevirtualinherited

Reimplemented in I2SConfigESP32, I2SConfigESP32V1, I2SConfigStd, and I2SConfigZephyr.

operator bool()

operator bool ( )

inlineinherited

Returns true if all components are defined (no component is 0)

operator!=() [1/2]

bool operator!= ( AudioInfo  alt )

inlineinherited

Returns true if alt values are the different from the current values.

operator!=() [2/2]

bool operator!= ( const USBAudioConfig &  other )

inline

operator==() [1/2]

bool operator== ( AudioInfo  alt )

inlineinherited

Returns true if alt values are the same like the current values.

operator==() [2/2]

bool operator== ( const USBAudioConfig &  other )

inline

set()

void set ( AudioInfo  info )

inlineinherited

Copies the values from info.

setAudioInfo()

void setAudioInfo ( AudioInfo  info )

inlineinherited

Same as set.

Member Data Documentation

begin_usb

bool begin_usb = false

When true (default), beginUSB() calls USB.begin() automatically. Set to false for composite USB (e.g. Audio + CDC): register all interfaces first, then call USB.begin() yourself.

bits_per_sample

uint8_t bits_per_sample = DEFAULT_BITS_PER_SAMPLE

inherited

Number of bits per sample (int16_t = 16 bits)

channels

uint16_t channels = DEFAULT_CHANNELS

inherited

Number of channels: 2=stereo, 1=mono.

enable_ep_in

bool enable_ep_in = true

device → host (capture / microphone)

enable_ep_in_flow_control

bool enable_ep_in_flow_control = true

Enable UAC2 IN-endpoint flow control: vary the per-frame isochronous packet size so non-integer sample-per-frame rates are delivered at the exact average rate. Without it the device sends a fixed (rounded-up) packet every frame, which makes e.g. 44100 Hz run at 45000 Hz effective (45 samples/ms instead of the required 44.1 average).

enable_ep_out

bool enable_ep_out = true

host → device (playback / speaker)

enable_feedback_ep

bool enable_feedback_ep = true

Enable isochronous feedback endpoint so the host can adjust its clock.

enable_interrupt_ep

bool enable_interrupt_ep = false

Enable the AC interrupt IN endpoint for device-initiated volume, mute, and sample-rate change notifications. Without it the host must poll via GET_CUR; the controls might still work, just without push updates.

enable_multi_sample_rate

bool enable_multi_sample_rate = false

When false (default): the clock source is fixed at sample_rate. The descriptor reports an internal fixed clock, and GET_RANGE returns only the configured rate. This avoids complex host negotiation. When true: the clock source is programmable and GET_RANGE returns the discrete rates listed in supported_sample_rates below. The host can change the rate via SET_CUR, and the descriptor wMaxPacketSize covers the highest rate in that list.

ep_fb

int16_t ep_fb = 0x86

ISO IN (explicit feedback, RX-only mode)

ep_in

int16_t ep_in = 0x85

ISO IN (device → host, capture/microphone)

Addresses must not conflict with other USB interfaces. On most platforms the -1 default (see USB_AUDIO_EP_* at the top of this file) lets the platform subclass allocate a free endpoint dynamically, which avoids conflicts automatically – including with CDC. Signed so a negative value (the -1 default on platforms without a fixed hardware endpoint) can be told apart from a real address: the platform subclass treats < 0 as "allocate dynamically" and any value you set >= 0 as a pinned address.

ep_int

int16_t ep_int = 0x87

INT IN (AC status/change notifications)

ep_out

int16_t ep_out = 0x05

ISO OUT (host → device, playback/speaker)

fifo_packets

uint8_t fifo_packets = 32

Depth of the audio FIFO expressed as a number of 1 ms packets. Larger values reduce the risk of underrun/overrun at the cost of latency. 32 packets (~32 ms at 44.1 kHz stereo 16-bit, ~6 kB RAM) is the minimum reliable value for RP2040 at 133 MHz: the I2S DMA write can block for 2-3 ms, and 16 packets leave no margin for those stalls.

itf_num_ac

uint8_t itf_num_ac = 0

Interface number of the Audio Control interface. Increment when other USB functions (CDC, HID …) occupy lower numbers.

manufacturer

const char* manufacturer = "Audio Tools"

max_power_ma

uint8_t max_power_ma = 100

pid

uint16_t pid = 0x4002

product

const char* product = "USB Audio"

sample_rate

sample_rate_t sample_rate = DEFAULT_SAMPLE_RATE

inherited

Sample Rate: e.g 44100.

self_powered

bool self_powered = true

serial

const char* serial = "000001"

supported_sample_rates

std::vector<uint32_t> supported_sample_rates

Initial value:

= {8000,  11025, 16000, 22050,
                                                   24000, 32000, 44100, 48000}

Discrete sample rates advertised in the Clock Source GET_RANGE response when enable_multi_sample_rate is true (ignored otherwise). Isochronous packet/buffer sizing for multi-rate mode is based on the LAST entry, so keep this sorted ascending – the host will never actually select a rate the GET_RANGE response didn't offer, so sizing for anything past the last entry would just waste buffer/FIFO space (and on MCUs with small USB FIFO RAM, such as ESP32-S2/S3's DWC2 peripheral, packets sized for an unreachably high rate can exceed the endpoint's available FIFO capacity entirely, silently breaking isochronous reception even though endpoint allocation and transfer arming both report success). Override before begin() to advertise a different set, e.g. just {44100, 48000}.

terminal_id

uint8_t terminal_id = 1

Terminal ID reported to Zephyr usbd_uac2 callbacks (ignored on TinyUSB). TX_MODE: Output Terminal ID (device → host, ISO IN). RX_MODE: Input Terminal ID (host → device, ISO OUT). Must match the UAC2 node topology in the board device tree.

vid

uint16_t vid = 0xCafe

volume_active

bool volume_active = false

When true we will process the volume and mute settings in the audio stream. When false we will not process the volume and mute settings but just provide the data for external processing.

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The documentation for this struct was generated from the following file:

• src/AudioTools/Communication/USB/USBAudioConfig.h