1 files changed, 778 insertions, 0 deletions

diff --git a/embassy-usb/src/class/uac1/speaker.rs b/embassy-usb/src/class/uac1/speaker.rs
new file mode 100644
index 000000000..96456d94a
--- /dev/null
+++ b/embassy-usb/src/class/uac1/speaker.rs
@@ -0,0 +1,778 @@
+//! USB Audio Class 1.0 - Speaker device
+//!
+//! Provides a class with a single audio streaming interface (host to device),
+//! that advertises itself as a speaker. Includes explicit sample rate feedback.
+//!
+//! Various aspects of the audio stream can be configured, for example:
+//! - sample rate
+//! - sample resolution
+//! - audio channel count and assignment
+//!
+//! The class provides volume and mute controls for each channel.
+
+use core::cell::{Cell, RefCell};
+use core::future::poll_fn;
+use core::marker::PhantomData;
+use core::sync::atomic::{AtomicBool, AtomicU32, Ordering};
+use core::task::Poll;
+
+use embassy_sync::blocking_mutex::CriticalSectionMutex;
+use embassy_sync::waitqueue::WakerRegistration;
+use heapless::Vec;
+
+use super::class_codes::*;
+use super::terminal_type::TerminalType;
+use super::{Channel, ChannelConfig, FeedbackRefresh, SampleWidth, MAX_AUDIO_CHANNEL_COUNT, MAX_AUDIO_CHANNEL_INDEX};
+use crate::control::{self, InResponse, OutResponse, Recipient, Request, RequestType};
+use crate::descriptor::{SynchronizationType, UsageType};
+use crate::driver::{Driver, Endpoint, EndpointError, EndpointIn, EndpointOut, EndpointType};
+use crate::types::InterfaceNumber;
+use crate::{Builder, Handler};
+
+/// Maximum allowed sampling rate (3 bytes) in Hz.
+const MAX_SAMPLE_RATE_HZ: u32 = 0x7FFFFF;
+
+/// Arbitrary unique identifier for the input unit.
+const INPUT_UNIT_ID: u8 = 0x01;
+
+/// Arbitrary unique identifier for the feature unit.
+const FEATURE_UNIT_ID: u8 = 0x02;
+
+/// Arbitrary unique identifier for the output unit.
+const OUTPUT_UNIT_ID: u8 = 0x03;
+
+// Volume settings go from -25600 to 0, in steps of 256.
+// Therefore, the volume settings are 8q8 values in units of dB.
+const VOLUME_STEPS_PER_DB: i16 = 256;
+const MIN_VOLUME_DB: i16 = -100;
+const MAX_VOLUME_DB: i16 = 0;
+
+// Maximum number of supported discrete sample rates.
+const MAX_SAMPLE_RATE_COUNT: usize = 10;
+
+/// The volume of an audio channel.
+#[derive(Debug, Clone, Copy)]
+#[cfg_attr(feature = "defmt", derive(defmt::Format))]
+pub enum Volume {
+    /// The channel is muted.
+    Muted,
+    /// The channel volume in dB. Ranges from `MIN_VOLUME_DB` (quietest) to `MAX_VOLUME_DB` (loudest).
+    DeciBel(f32),
+}
+
+/// Internal state for the USB Audio Class.
+pub struct State<'d> {
+    control: Option<Control<'d>>,
+    shared: SharedControl<'d>,
+}
+
+impl<'d> Default for State<'d> {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl<'d> State<'d> {
+    /// Create a new `State`.
+    pub fn new() -> Self {
+        Self {
+            control: None,
+            shared: SharedControl::default(),
+        }
+    }
+}
+
+/// Implementation of the USB audio class 1.0.
+pub struct Speaker<'d, D: Driver<'d>> {
+    phantom: PhantomData<&'d D>,
+}
+
+impl<'d, D: Driver<'d>> Speaker<'d, D> {
+    /// Creates a new [`Speaker`] device, split into a stream, feedback, and a control change notifier.
+    ///
+    /// The packet size should be chosen, based on the expected transfer size of samples per (micro)frame.
+    /// For example, a stereo stream at 32 bit resolution and 48 kHz sample rate yields packets of 384 byte for
+    /// full-speed USB (1 ms frame interval) or 48 byte for high-speed USB (125 us microframe interval).
+    /// When using feedback, the packet size varies and thus, the `max_packet_size` should be increased (e.g. to double).
+    ///
+    /// # Arguments
+    ///
+    /// * `builder` - The builder for the class.
+    /// * `state` - The internal state of the class.
+    /// * `max_packet_size` - The maximum packet size per (micro)frame.
+    /// * `resolution` - The audio sample resolution.
+    /// * `sample_rates_hz` - The supported sample rates in Hz.
+    /// * `channels` - The advertised audio channels (up to 12). Entries must be unique, or this function panics.
+    /// * `feedback_refresh_period` - The refresh period for the feedback value.
+    pub fn new(
+        builder: &mut Builder<'d, D>,
+        state: &'d mut State<'d>,
+        max_packet_size: u16,
+        resolution: SampleWidth,
+        sample_rates_hz: &[u32],
+        channels: &'d [Channel],
+        feedback_refresh_period: FeedbackRefresh,
+    ) -> (Stream<'d, D>, Feedback<'d, D>, ControlMonitor<'d>) {
+        // The class and subclass fields of the IAD aren't required to match the class and subclass fields of
+        // the interfaces in the interface collection that the IAD describes. Microsoft recommends that
+        // the first interface of the collection has class and subclass fields that match the class and
+        // subclass fields of the IAD.
+        let mut func = builder.function(USB_AUDIO_CLASS, USB_AUDIOCONTROL_SUBCLASS, PROTOCOL_NONE);
+
+        // Audio control interface (mandatory) [UAC 4.3.1]
+        let mut interface = func.interface();
+        let control_interface = interface.interface_number().into();
+        let streaming_interface = u8::from(control_interface) + 1;
+        let mut alt = interface.alt_setting(USB_AUDIO_CLASS, USB_AUDIOCONTROL_SUBCLASS, PROTOCOL_NONE, None);
+
+        // Terminal topology:
+        // Input terminal (receives audio stream) -> Feature Unit (mute and volume) -> Output terminal (e.g. towards speaker)
+
+        // =======================================
+        // Input Terminal Descriptor [UAC 3.3.2.1]
+        // Audio input
+        let terminal_type: u16 = TerminalType::UsbStreaming.into();
+
+        // Assemble channel configuration field
+        let mut channel_config: u16 = ChannelConfig::None.into();
+        for channel in channels {
+            let channel: u16 = channel.get_channel_config().into();
+
+            if channel_config & channel != 0 {
+                panic!("Invalid channel config, duplicate channel {}.", channel);
+            }
+            channel_config |= channel;
+        }
+
+        let input_terminal_descriptor = [
+            INPUT_TERMINAL, // bDescriptorSubtype
+            INPUT_UNIT_ID,  // bTerminalID
+            terminal_type as u8,
+            (terminal_type >> 8) as u8, // wTerminalType
+            0x00,                       // bAssocTerminal (none)
+            channels.len() as u8,       // bNrChannels
+            channel_config as u8,
+            (channel_config >> 8) as u8, // wChannelConfig
+            0x00,                        // iChannelNames (none)
+            0x00,                        // iTerminal (none)
+        ];
+
+        // ========================================
+        // Output Terminal Descriptor [UAC 4.3.2.2]
+        // Speaker output
+        let terminal_type: u16 = TerminalType::OutSpeaker.into();
+        let output_terminal_descriptor = [
+            OUTPUT_TERMINAL, // bDescriptorSubtype
+            OUTPUT_UNIT_ID,  // bTerminalID
+            terminal_type as u8,
+            (terminal_type >> 8) as u8, // wTerminalType
+            0x00,                       // bAssocTerminal (none)
+            FEATURE_UNIT_ID,            // bSourceID (the feature unit)
+            0x00,                       // iTerminal (none)
+        ];
+
+        // =====================================
+        // Feature Unit Descriptor [UAC 4.3.2.5]
+        // Mute and volume control
+        let controls = MUTE_CONTROL | VOLUME_CONTROL;
+
+        const FEATURE_UNIT_DESCRIPTOR_SIZE: usize = 5;
+        let mut feature_unit_descriptor: Vec<u8, { FEATURE_UNIT_DESCRIPTOR_SIZE + MAX_AUDIO_CHANNEL_COUNT + 1 }> =
+            Vec::from_slice(&[
+                FEATURE_UNIT,         // bDescriptorSubtype (Feature Unit)
+                FEATURE_UNIT_ID,      // bUnitID
+                INPUT_UNIT_ID,        // bSourceID
+                1,                    // bControlSize (one byte per control)
+                FU_CONTROL_UNDEFINED, // Master controls (disabled, use only per-channel control)
+            ])
+            .unwrap();
+
+        // Add per-channel controls
+        for _channel in channels {
+            feature_unit_descriptor.push(controls).unwrap();
+        }
+        feature_unit_descriptor.push(0x00).unwrap(); // iFeature (none)
+
+        // ===============================================
+        // Format desciptor [UAC 4.5.3]
+        // Used later, for operational streaming interface
+        let mut format_descriptor: Vec<u8, { 6 + 3 * MAX_SAMPLE_RATE_COUNT }> = Vec::from_slice(&[
+            FORMAT_TYPE,               // bDescriptorSubtype
+            FORMAT_TYPE_I,             // bFormatType
+            channels.len() as u8,      // bNrChannels
+            resolution as u8,          // bSubframeSize
+            resolution.in_bit() as u8, // bBitResolution
+        ])
+        .unwrap();
+
+        format_descriptor.push(sample_rates_hz.len() as u8).unwrap();
+
+        for sample_rate_hz in sample_rates_hz {
+            assert!(*sample_rate_hz <= MAX_SAMPLE_RATE_HZ);
+            format_descriptor.push((sample_rate_hz & 0xFF) as u8).unwrap();
+            format_descriptor.push(((sample_rate_hz >> 8) & 0xFF) as u8).unwrap();
+            format_descriptor.push(((sample_rate_hz >> 16) & 0xFF) as u8).unwrap();
+        }
+
+        // ==================================================
+        // Class-specific AC Interface Descriptor [UAC 4.3.2]
+        const DESCRIPTOR_HEADER_SIZE: usize = 2;
+        const INTERFACE_DESCRIPTOR_SIZE: usize = 7;
+
+        let mut total_descriptor_length = 0;
+
+        for size in [
+            INTERFACE_DESCRIPTOR_SIZE,
+            input_terminal_descriptor.len(),
+            feature_unit_descriptor.len(),
+            output_terminal_descriptor.len(),
+        ] {
+            total_descriptor_length += size + DESCRIPTOR_HEADER_SIZE;
+        }
+
+        let interface_descriptor: [u8; INTERFACE_DESCRIPTOR_SIZE] = [
+            HEADER_SUBTYPE, // bDescriptorSubtype (Header)
+            ADC_VERSION as u8,
+            (ADC_VERSION >> 8) as u8, // bcdADC
+            total_descriptor_length as u8,
+            (total_descriptor_length >> 8) as u8, // wTotalLength
+            0x01,                                 // bInCollection (1 streaming interface)
+            streaming_interface,                  // baInterfaceNr
+        ];
+
+        alt.descriptor(CS_INTERFACE, &interface_descriptor);
+        alt.descriptor(CS_INTERFACE, &input_terminal_descriptor);
+        alt.descriptor(CS_INTERFACE, &feature_unit_descriptor);
+        alt.descriptor(CS_INTERFACE, &output_terminal_descriptor);
+
+        // =====================================================
+        // Audio streaming interface, zero-bandwidth [UAC 4.5.1]
+        let mut interface = func.interface();
+        let alt = interface.alt_setting(USB_AUDIO_CLASS, USB_AUDIOSTREAMING_SUBCLASS, PROTOCOL_NONE, None);
+        drop(alt);
+
+        // ==================================================
+        // Audio streaming interface, operational [UAC 4.5.1]
+        let mut alt = interface.alt_setting(USB_AUDIO_CLASS, USB_AUDIOSTREAMING_SUBCLASS, PROTOCOL_NONE, None);
+
+        alt.descriptor(
+            CS_INTERFACE,
+            &[
+                AS_GENERAL,    // bDescriptorSubtype
+                INPUT_UNIT_ID, // bTerminalLink
+                0x00,          // bDelay (none)
+                PCM as u8,
+                (PCM >> 8) as u8, // wFormatTag (PCM format)
+            ],
+        );
+
+        alt.descriptor(CS_INTERFACE, &format_descriptor);
+
+        let streaming_endpoint = alt.alloc_endpoint_out(EndpointType::Isochronous, max_packet_size, 1);
+        let feedback_endpoint = alt.alloc_endpoint_in(
+            EndpointType::Isochronous,
+            4, // Feedback packets are 24 bit (10.14 format).
+            1,
+        );
+
+        // Write the descriptor for the streaming endpoint, after knowing the address of the feedback endpoint.
+        alt.endpoint_descriptor(
+            streaming_endpoint.info(),
+            SynchronizationType::Asynchronous,
+            UsageType::DataEndpoint,
+            &[
+                0x00,                                 // bRefresh (0)
+                feedback_endpoint.info().addr.into(), // bSynchAddress (the feedback endpoint)
+            ],
+        );
+
+        alt.descriptor(
+            CS_ENDPOINT,
+            &[
+                AS_GENERAL,            // bDescriptorSubtype (General)
+                SAMPLING_FREQ_CONTROL, // bmAttributes (support sampling frequency control)
+                0x02,                  // bLockDelayUnits (PCM)
+                0x0000 as u8,
+                (0x0000 >> 8) as u8, // wLockDelay (0)
+            ],
+        );
+
+        // Write the feedback endpoint descriptor after the streaming endpoint descriptor
+        // This is demanded by the USB audio class specification.
+        alt.endpoint_descriptor(
+            feedback_endpoint.info(),
+            SynchronizationType::NoSynchronization,
+            UsageType::FeedbackEndpoint,
+            &[
+                feedback_refresh_period as u8, // bRefresh
+                0x00,                          // bSynchAddress (none)
+            ],
+        );
+
+        // Free up the builder.
+        drop(func);
+
+        // Store channel information
+        state.shared.channels = channels;
+
+        state.control = Some(Control {
+            shared: &state.shared,
+            streaming_endpoint_address: streaming_endpoint.info().addr.into(),
+            control_interface_number: control_interface,
+        });
+
+        builder.handler(state.control.as_mut().unwrap());
+
+        let control = &state.shared;
+
+        (
+            Stream { streaming_endpoint },
+            Feedback { feedback_endpoint },
+            ControlMonitor { shared: control },
+        )
+    }
+}
+
+/// Audio settings for the feature unit.
+///
+/// Contains volume and mute control.
+#[derive(Clone, Copy, Debug)]
+#[cfg_attr(feature = "defmt", derive(defmt::Format))]
+pub struct AudioSettings {
+    /// Channel mute states.
+    muted: [bool; MAX_AUDIO_CHANNEL_COUNT],
+    /// Channel volume levels in 8.8 format (in dB).
+    volume_8q8_db: [i16; MAX_AUDIO_CHANNEL_COUNT],
+}
+
+impl Default for AudioSettings {
+    fn default() -> Self {
+        AudioSettings {
+            muted: [true; MAX_AUDIO_CHANNEL_COUNT],
+            volume_8q8_db: [MAX_VOLUME_DB * VOLUME_STEPS_PER_DB; MAX_AUDIO_CHANNEL_COUNT],
+        }
+    }
+}
+
+struct Control<'d> {
+    control_interface_number: InterfaceNumber,
+    streaming_endpoint_address: u8,
+    shared: &'d SharedControl<'d>,
+}
+
+/// Shared data between [`Control`] and the [`Speaker`] class.
+struct SharedControl<'d> {
+    /// The collection of audio settings (volumes, mute states).
+    audio_settings: CriticalSectionMutex<Cell<AudioSettings>>,
+
+    /// Channel assignments.
+    channels: &'d [Channel],
+
+    /// The audio sample rate in Hz.
+    sample_rate_hz: AtomicU32,
+
+    // Notification mechanism.
+    waker: RefCell<WakerRegistration>,
+    changed: AtomicBool,
+}
+
+impl<'d> Default for SharedControl<'d> {
+    fn default() -> Self {
+        SharedControl {
+            audio_settings: CriticalSectionMutex::new(Cell::new(AudioSettings::default())),
+            channels: &[],
+            sample_rate_hz: AtomicU32::new(0),
+            waker: RefCell::new(WakerRegistration::new()),
+            changed: AtomicBool::new(false),
+        }
+    }
+}
+
+impl<'d> SharedControl<'d> {
+    async fn changed(&self) {
+        poll_fn(|context| {
+            if self.changed.load(Ordering::Relaxed) {
+                self.changed.store(false, Ordering::Relaxed);
+                Poll::Ready(())
+            } else {
+                self.waker.borrow_mut().register(context.waker());
+                Poll::Pending
+            }
+        })
+        .await;
+    }
+}
+
+/// Used for reading audio frames.
+pub struct Stream<'d, D: Driver<'d>> {
+    streaming_endpoint: D::EndpointOut,
+}
+
+impl<'d, D: Driver<'d>> Stream<'d, D> {
+    /// Reads a single packet from the OUT endpoint
+    pub async fn read_packet(&mut self, data: &mut [u8]) -> Result<usize, EndpointError> {
+        self.streaming_endpoint.read(data).await
+    }
+
+    /// Waits for the USB host to enable this interface
+    pub async fn wait_connection(&mut self) {
+        self.streaming_endpoint.wait_enabled().await;
+    }
+}
+
+/// Used for writing sample rate information over the feedback endpoint.
+pub struct Feedback<'d, D: Driver<'d>> {
+    feedback_endpoint: D::EndpointIn,
+}
+
+impl<'d, D: Driver<'d>> Feedback<'d, D> {
+    /// Writes a single packet into the IN endpoint.
+    pub async fn write_packet(&mut self, data: &[u8]) -> Result<(), EndpointError> {
+        self.feedback_endpoint.write(data).await
+    }
+
+    /// Waits for the USB host to enable this interface.
+    pub async fn wait_connection(&mut self) {
+        self.feedback_endpoint.wait_enabled().await;
+    }
+}
+
+/// Control status change monitor
+///
+/// Await [`ControlMonitor::changed`] for being notified of configuration changes. Afterwards, the updated
+/// configuration settings can be read with [`ControlMonitor::volume`] and [`ControlMonitor::sample_rate_hz`].
+pub struct ControlMonitor<'d> {
+    shared: &'d SharedControl<'d>,
+}
+
+impl<'d> ControlMonitor<'d> {
+    fn audio_settings(&self) -> AudioSettings {
+        let audio_settings = self.shared.audio_settings.lock(|x| x.get());
+
+        audio_settings
+    }
+
+    fn get_logical_channel(&self, search_channel: Channel) -> Option<usize> {
+        let index = self.shared.channels.iter().position(|&c| c == search_channel)?;
+
+        // The logical channels start at one (zero is the master channel).
+        Some(index + 1)
+    }
+
+    /// Get the volume of a selected channel.
+    pub fn volume(&self, channel: Channel) -> Option<Volume> {
+        let channel_index = self.get_logical_channel(channel)?;
+
+        if self.audio_settings().muted[channel_index] {
+            return Some(Volume::Muted);
+        }
+
+        Some(Volume::DeciBel(
+            (self.audio_settings().volume_8q8_db[channel_index] as f32) / 256.0f32,
+        ))
+    }
+
+    /// Get the streaming endpoint's sample rate in Hz.
+    pub fn sample_rate_hz(&self) -> u32 {
+        self.shared.sample_rate_hz.load(Ordering::Relaxed)
+    }
+
+    /// Return a future for when the control settings change.
+    pub async fn changed(&self) {
+        self.shared.changed().await;
+    }
+}
+
+impl<'d> Control<'d> {
+    fn changed(&mut self) {
+        self.shared.changed.store(true, Ordering::Relaxed);
+        self.shared.waker.borrow_mut().wake();
+    }
+
+    fn interface_set_mute_state(
+        &mut self,
+        audio_settings: &mut AudioSettings,
+        channel_index: u8,
+        data: &[u8],
+    ) -> OutResponse {
+        let mute_state = data[0] != 0;
+
+        match channel_index as usize {
+            ..=MAX_AUDIO_CHANNEL_INDEX => {
+                audio_settings.muted[channel_index as usize] = mute_state;
+            }
+            _ => {
+                debug!("Failed to set channel {} mute state: {}", channel_index, mute_state);
+                return OutResponse::Rejected;
+            }
+        }
+
+        debug!("Set channel {} mute state: {}", channel_index, mute_state);
+        OutResponse::Accepted
+    }
+
+    fn interface_set_volume(
+        &mut self,
+        audio_settings: &mut AudioSettings,
+        channel_index: u8,
+        data: &[u8],
+    ) -> OutResponse {
+        let volume = i16::from_ne_bytes(data[..2].try_into().expect("Failed to read volume."));
+
+        match channel_index as usize {
+            ..=MAX_AUDIO_CHANNEL_INDEX => {
+                audio_settings.volume_8q8_db[channel_index as usize] = volume;
+            }
+            _ => {
+                debug!("Failed to set channel {} volume: {}", channel_index, volume);
+                return OutResponse::Rejected;
+            }
+        }
+
+        debug!("Set channel {} volume: {}", channel_index, volume);
+        OutResponse::Accepted
+    }
+
+    fn interface_set_request(&mut self, req: control::Request, data: &[u8]) -> Option<OutResponse> {
+        let interface_number = req.index as u8;
+        let entity_index = (req.index >> 8) as u8;
+        let channel_index = req.value as u8;
+        let control_unit = (req.value >> 8) as u8;
+
+        if interface_number != self.control_interface_number.into() {
+            debug!("Unhandled interface set request for interface {}", interface_number);
+            return None;
+        }
+
+        if entity_index != FEATURE_UNIT_ID {
+            debug!("Unsupported interface set request for entity {}", entity_index);
+            return Some(OutResponse::Rejected);
+        }
+
+        if req.request != SET_CUR {
+            debug!("Unsupported interface set request type {}", req.request);
+            return Some(OutResponse::Rejected);
+        }
+
+        let mut audio_settings = self.shared.audio_settings.lock(|x| x.get());
+        let response = match control_unit {
+            MUTE_CONTROL => self.interface_set_mute_state(&mut audio_settings, channel_index, data),
+            VOLUME_CONTROL => self.interface_set_volume(&mut audio_settings, channel_index, data),
+            _ => OutResponse::Rejected,
+        };
+
+        if response == OutResponse::Rejected {
+            return Some(response);
+        }
+
+        // Store updated settings
+        self.shared.audio_settings.lock(|x| x.set(audio_settings));
+
+        self.changed();
+
+        Some(OutResponse::Accepted)
+    }
+
+    fn endpoint_set_request(&mut self, req: control::Request, data: &[u8]) -> Option<OutResponse> {
+        let control_selector = (req.value >> 8) as u8;
+        let endpoint_address = req.index as u8;
+
+        if endpoint_address != self.streaming_endpoint_address {
+            debug!(
+                "Unhandled endpoint set request for endpoint {} and control {} with data {}",
+                endpoint_address, control_selector, data
+            );
+            return None;
+        }
+
+        if control_selector != SAMPLING_FREQ_CONTROL {
+            debug!(
+                "Unsupported endpoint set request for control selector {}",
+                control_selector
+            );
+            return Some(OutResponse::Rejected);
+        }
+
+        let sample_rate_hz: u32 = (data[0] as u32) | (data[1] as u32) << 8 | (data[2] as u32) << 16;
+        self.shared.sample_rate_hz.store(sample_rate_hz, Ordering::Relaxed);
+
+        debug!("Set endpoint {} sample rate to {} Hz", endpoint_address, sample_rate_hz);
+
+        self.changed();
+
+        Some(OutResponse::Accepted)
+    }
+
+    fn interface_get_request<'r>(&'r mut self, req: Request, buf: &'r mut [u8]) -> Option<InResponse<'r>> {
+        let interface_number = req.index as u8;
+        let entity_index = (req.index >> 8) as u8;
+        let channel_index = req.value as u8;
+        let control_unit = (req.value >> 8) as u8;
+
+        if interface_number != self.control_interface_number.into() {
+            debug!("Unhandled interface get request for interface {}.", interface_number);
+            return None;
+        }
+
+        if entity_index != FEATURE_UNIT_ID {
+            // Only this function unit can be handled at the moment.
+            debug!("Unsupported interface get request for entity {}.", entity_index);
+            return Some(InResponse::Rejected);
+        }
+
+        let audio_settings = self.shared.audio_settings.lock(|x| x.get());
+
+        match req.request {
+            GET_CUR => match control_unit {
+                VOLUME_CONTROL => {
+                    let volume: i16;
+
+                    match channel_index as usize {
+                        ..=MAX_AUDIO_CHANNEL_INDEX => volume = audio_settings.volume_8q8_db[channel_index as usize],
+                        _ => return Some(InResponse::Rejected),
+                    }
+
+                    buf[0] = volume as u8;
+                    buf[1] = (volume >> 8) as u8;
+
+                    debug!("Got channel {} volume: {}.", channel_index, volume);
+                    return Some(InResponse::Accepted(&buf[..2]));
+                }
+                MUTE_CONTROL => {
+                    let mute_state: bool;
+
+                    match channel_index as usize {
+                        ..=MAX_AUDIO_CHANNEL_INDEX => mute_state = audio_settings.muted[channel_index as usize],
+                        _ => return Some(InResponse::Rejected),
+                    }
+
+                    buf[0] = mute_state.into();
+                    debug!("Got channel {} mute state: {}.", channel_index, mute_state);
+                    return Some(InResponse::Accepted(&buf[..1]));
+                }
+                _ => return Some(InResponse::Rejected),
+            },
+            GET_MIN => match control_unit {
+                VOLUME_CONTROL => {
+                    let min_volume = MIN_VOLUME_DB * VOLUME_STEPS_PER_DB;
+                    buf[0] = min_volume as u8;
+                    buf[1] = (min_volume >> 8) as u8;
+                    return Some(InResponse::Accepted(&buf[..2]));
+                }
+                _ => return Some(InResponse::Rejected),
+            },
+            GET_MAX => match control_unit {
+                VOLUME_CONTROL => {
+                    let max_volume = MAX_VOLUME_DB * VOLUME_STEPS_PER_DB;
+                    buf[0] = max_volume as u8;
+                    buf[1] = (max_volume >> 8) as u8;
+                    return Some(InResponse::Accepted(&buf[..2]));
+                }
+                _ => return Some(InResponse::Rejected),
+            },
+            GET_RES => match control_unit {
+                VOLUME_CONTROL => {
+                    buf[0] = VOLUME_STEPS_PER_DB as u8;
+                    buf[1] = (VOLUME_STEPS_PER_DB >> 8) as u8;
+                    return Some(InResponse::Accepted(&buf[..2]));
+                }
+                _ => return Some(InResponse::Rejected),
+            },
+            _ => return Some(InResponse::Rejected),
+        }
+    }
+
+    fn endpoint_get_request<'r>(&'r mut self, req: Request, buf: &'r mut [u8]) -> Option<InResponse<'r>> {
+        let control_selector = (req.value >> 8) as u8;
+        let endpoint_address = req.index as u8;
+
+        if endpoint_address != self.streaming_endpoint_address {
+            debug!("Unhandled endpoint get request for endpoint {}.", endpoint_address);
+            return None;
+        }
+
+        if control_selector != SAMPLING_FREQ_CONTROL as u8 {
+            debug!(
+                "Unsupported endpoint get request for control selector {}.",
+                control_selector
+            );
+            return Some(InResponse::Rejected);
+        }
+
+        let sample_rate_hz = self.shared.sample_rate_hz.load(Ordering::Relaxed);
+
+        buf[0] = (sample_rate_hz & 0xFF) as u8;
+        buf[1] = ((sample_rate_hz >> 8) & 0xFF) as u8;
+        buf[2] = ((sample_rate_hz >> 16) & 0xFF) as u8;
+
+        Some(InResponse::Accepted(&buf[..3]))
+    }
+}
+
+impl<'d> Handler for Control<'d> {
+    /// Called when the USB device has been enabled or disabled.
+    fn enabled(&mut self, enabled: bool) {
+        debug!("USB device enabled: {}", enabled);
+    }
+
+    /// Called when the host has set the address of the device to `addr`.
+    fn addressed(&mut self, addr: u8) {
+        debug!("Host set address to: {}", addr);
+    }
+
+    /// Called when the host has enabled or disabled the configuration of the device.
+    fn configured(&mut self, configured: bool) {
+        debug!("USB device configured: {}", configured);
+    }
+
+    /// Called when remote wakeup feature is enabled or disabled.
+    fn remote_wakeup_enabled(&mut self, enabled: bool) {
+        debug!("USB remote wakeup enabled: {}", enabled);
+    }
+
+    /// Called when a "set alternate setting" control request is done on the interface.
+    fn set_alternate_setting(&mut self, iface: InterfaceNumber, alternate_setting: u8) {
+        debug!(
+            "USB set interface number {} to alt setting {}.",
+            iface, alternate_setting
+        );
+    }
+
+    /// Called after a USB reset after the bus reset sequence is complete.
+    fn reset(&mut self) {
+        let shared = self.shared;
+        shared.audio_settings.lock(|x| x.set(AudioSettings::default()));
+
+        shared.changed.store(true, Ordering::Relaxed);
+        shared.waker.borrow_mut().wake();
+    }
+
+    /// Called when the bus has entered or exited the suspend state.
+    fn suspended(&mut self, suspended: bool) {
+        debug!("USB device suspended: {}", suspended);
+    }
+
+    // Handle control set requests.
+    fn control_out(&mut self, req: control::Request, data: &[u8]) -> Option<OutResponse> {
+        match req.request_type {
+            RequestType::Class => match req.recipient {
+                Recipient::Interface => self.interface_set_request(req, data),
+                Recipient::Endpoint => self.endpoint_set_request(req, data),
+                _ => Some(OutResponse::Rejected),
+            },
+            _ => None,
+        }
+    }
+
+    // Handle control get requests.
+    fn control_in<'a>(&'a mut self, req: Request, buf: &'a mut [u8]) -> Option<InResponse<'a>> {
+        match req.request_type {
+            RequestType::Class => match req.recipient {
+                Recipient::Interface => self.interface_get_request(req, buf),
+                Recipient::Endpoint => self.endpoint_get_request(req, buf),
+                _ => None,
+            },
+            _ => None,
+        }
+    }
+}