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# 3.2.4 Library Interface

This section describes the Application Programming Interface (API) functions of the USB Host Layer Library. Refer to each section for a detailed description.

## Functions

Name | Description
USB_HOST_Deinitialize | Deinitializes the specified instance of the USB Host Layer.
USB_HOST_Status | Gets the current status of the USB Host Layer.
USB_HOST_Tasks | Maintains the USB Host Layer state machine.
USB_HOST_BusEnable | Starts host operations.
USB_HOST_BusIsEnabled | Checks if the bus is enabled.
USB_HOST_BusIsSuspended | Returns the suspend status of the bus.
USB_HOST_BusResume | Resumes the bus.
USB_HOST_BusSuspend | Suspends the bus.
USB_HOST_DeviceGetFirst | Returns information about the first attached device on the bus.
USB_HOST_DeviceGetNext | Returns information about the next device on the bus.
USB_HOST_DeviceIsSuspended | Returns the suspend state of the device is suspended.
USB_HOST_DeviceResume | Resumes the selected device.
USB_HOST_DeviceSpeedGet | Returns the speed at which this device is operating.
USB_HOST_DeviceStringDescriptorGet | Retrieves specified string descriptor from the device.
USB_HOST_DeviceSuspend | Suspends the specified device.
USB_HOST_EventHandlerSet | USB Host Layer Event Handler Callback Function set function.
USB_HOST_Initialize | Initializes the USB Host layer instance specified by the index.

## Data Types and Constants

Name | Description
USB_HOST_INIT | Defines the data required to initialize a USB Host Layer instance.
USB_HOST_EVENT_RESPONSE | Host Layer Events Handler Function Response Type.
TPL_INTERFACE_CLASS_SUBCLASS_PROTOCOL | Attach client driver to interface based on Class, Subclass and Protocol.
TPL_INTERFACE_CLASS_SUBCLASS | Attach client driver based on Class and Subclass only.
TPL_INTERFACE_CLASS | Attach client driver based on Class only.
TPL_INTERFACE_ANY | Attach client driver to all interfaces.
TPL_DEVICE_VID_PID | Attach client driver to interface based on VID and PID.
TPL_DEVICE_VID_PID_MASKED | Attach client driver to interface based on VID and a masked PID.
TPL_DEVICE_ANY | Attach client driver to all devices.
USB_HOST_BUS | Defines a USB Bus Data Type.
USB_HOST_DEVICE_INFO | Defines the data type that is used by the USB_HOST_DeviceGetFirst() and USB_HOST_DeviceGetNext() functions.
USB_HOST_DEVICE_OBJ_HANDLE | Handle to an attached USB Device.
USB_HOST_DEVICE_STRING | Defines a defines types of strings that can be request through the USB_HOST_DeviceStringDescriptorGet() function.
USB_HOST_EVENT | Defines the different events that the USB Host Layer can generate.
USB_HOST_EVENT_HANDLER | USB Host Layer Event Handler Function Pointer Type.
USB_HOST_HCD | Defines the USB Host HCD Information object that is provided to the host layer.
USB_HOST_REQUEST_HANDLE | USB Host Request Handle Type.
USB_HOST_RESULT | USB Host Results.
USB_HOST_STRING_REQUEST_COMPLETE_CALLBACK | USB Host Device String Descriptor Request Complete Callback Function Type.
USB_HOST_BUS_ALL | USB Host Bus All.
USB_HOST_DEVICE_OBJ_HANDLE_INVALID | Defines an invalid USB Device Object Handle.
USB_HOST_DEVICE_STRING_LANG_ID_DEFAULT | Defines the default Lang ID to be used while obtaining the string.
USB_HOST_REQUEST_HANDLE_INVALID | USB Host Request Invalid Handle.
USB_HOST_RESULT_MIN | USB Host Result Minimum Constant.