Crate embassy_usb

embassy-usb

Async USB device stack for embedded devices in Rust.

Features

• Native async.
• Fully lock-free: endpoints are separate objects that can be used independently without needing a central mutex. If the driver supports it, they can even be used from different priority levels.
• Suspend/resume, remote wakeup.
• USB composite devices.
• Ergonomic descriptor builder.
• Ready-to-use implementations for a few USB classes (note you can still implement any class yourself outside the crate).
  • Serial ports (CDC ACM)
  • Ethernet (CDC NCM)
  • Human Interface Devices (HID)
  • MIDI

Adding support for new hardware

To add embassy-usb support for new hardware (i.e. a new MCU chip), you have to write a driver that implements the embassy-usb-driver traits.

Driver crates should depend only on embassy-usb-driver, not on the main embassy-usb crate. This allows existing drivers to continue working for newer embassy-usb major versions, without needing an update, if the driver trait has not had breaking changes.

Configuration

embassy-usb has some configuration settings that are set at compile time, affecting sizes and counts of buffers.

They can be set in two ways:

• Via Cargo features: enable a feature like <name>-<value>. name must be in lowercase and use dashes instead of underscores. For example. max-interface-count-3. Only a selection of values is available, check Cargo.toml for the list.
• Via environment variables at build time: set the variable named EMBASSY_USB_<value>. For example EMBASSY_USB_MAX_INTERFACE_COUNT=3 cargo build. You can also set them in the [env] section of .cargo/config.toml. Any value can be set, unlike with Cargo features.

Environment variables take precedence over Cargo features. If two Cargo features are enabled for the same setting with different values, compilation fails.

MAX_INTERFACE_COUNT

Max amount of interfaces that can be created in one device. Default: 4.

Interoperability

This crate can run on any executor.

Re-exports

• pub use embassy_usb_driver as driver;

Modules

• class
  Implementations of well-known USB classes.
• control
  USB control data types.
• descriptor
  Utilities for writing USB descriptors.
• msos
  Microsoft OS Descriptors
• types
  USB types.

Structs

• Builder
  UsbDevice builder.
• Config
  Configuration used when creating UsbDevice.
• FunctionBuilder
  Function builder.
• InterfaceAltBuilder
  Interface alternate setting builder.
• InterfaceBuilder
  Interface builder.
• UsbBufferReport
  A report of the used size of the runtime allocated buffers
• UsbDevice
  Main struct for the USB device stack.

Enums

• RemoteWakeupError
  Error returned by UsbDevice::remote_wakeup.
• UsbDeviceState
  The global state of the USB device.
• UsbVersion
  Allows Configuring the Bcd USB version below 2.1

Constants

• CONFIGURATION_NONE
  The bConfiguration value for the not configured state.
• CONFIGURATION_VALUE
  The bConfiguration value for the single configuration supported by this device.

Traits

• Handler
  Handler for device events and control requests.