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Configure USB endpoints in a USB host controller driver

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UCX manages the creation of endpoint objects, and notifies the host controller to program or deprogram endpoints into the USB host controller.

While an endpoint is programmed, it is also managed by UCX. The state of an endpoint changes as devices are connected to and disconnect from the bus, experience power events such as suspend and reset, and undergo new endpoint creation such as alternate setting changes.

Endpoint configuration

UCX invokes callback functions implemented by the host controller driver to notify the driver when endpoints must programmed into the USB host controller, or released. When EVT_UCX_USBDEVICE_ENABLE is called, the driver prepares the controller for performing transfers to the device's default endpoint. Preparing the controller includes programming the default endpoint. When EVT_UCX_USBDEVICE_DISABLE is called, the driver deprograms the default endpoint and frees other controller resources associated with the device. When EVT_UCX_USBDEVICE_ENDPOINTS_CONFIGURE is called, the driver is given a list of non-default endpoints to program into the controller, and given another list of non-default endpoints to remove from the controller. The host controller driver then programs the specified non-default endpoints into the controller, and also removes the non-default endpoints (specified in the other list) from the controller.

Queue state management

UCX invokes callback functions implemented by the host controller driver to perform changes to the endpoint queue state. The driver then takes the corresponding action on the endpoint queue given to UCX, and on any second level queues maintained within the driver. Endpoint queues are aborted or purged in these scenarios:

  • The USB device client driver sends an URB_FUNCTION_ABORT_PIPE request.
  • During suspend.
  • When the hub that a device is attached to, detects a device disconnection.
  • During a select-interface setting request.

To notify the host controller driver about a queue abort or purge, UCX calls EVT_UCX_ENDPOINT_ABORT or EVT_UCX_ENDPOINT_PURGE. If at some later point the endpoint queue is needed by UCX, then UCX invokes the EVT_UCX_ENDPOINT_START callback to notify the driver to start the queue.

Transfer cancellation

For any controller for which the host controller driver declares GUID_USB_CAPABILITY_CLEAR_TT_BUFFER_ON_ASYNC_TRANSFER_CANCEL, the driver must call UcxEndpointNeedToCancelTransfers and implement EVT_UCX_ENDPOINT_OK_TO_CANCEL_TRANSFERS for canceling asynchronous (Bulk or Control) USB transfers to a USB full or low speed device that is behind a Transaction Translator (TT) hub. In all other cases, the driver can optionally call UcxEndpointNeedToCancelTransfers to get a EVT_UCX_ENDPOINT_OK_TO_CANCEL_TRANSFERS notification that indicates that cancelling transfers is allowed on this endpoint and the driver can proceed to cancel the transfers. Alternatively, the driver can cancel transfers directly without calling UcxEndpointNeedToCancelTransfers.

If the host controller driver always fails the request for this GUID, it can ignore these two function calls entirely.

If the driver never calls UcxEndpointNeedToCancelTransfers, the driver's EVT_UCX_ENDPOINT_OK_TO_CANCEL_TRANSFERS callback is not called and can be NULL during callback registration.

If the driver intends to use UcxEndpointNeedToCancelTransfers, the driver must call the method when a transfer has been programmed into the controller and then canceled, and then waits for EVT_UCX_ENDPOINT_OK_TO_CANCEL_TRANSFERS before completing it.