Periodic Interrupt-IN Transfers

Periodic or polled interrupt-IN transfers execute on input requests which do not have the USB_ATTRS_ONE_XFER attribute set. One request enables repetitive transfers at a periodic rate set by the endpoint's bInterval. There can be only one interrupt-IN request submitted at a time.

Periodic interrupt-IN transfers are always asynchronous. Client driver notification of new data is always via a callback. The USB_FLAGS_SLEEP flag is only to wait for resources to become available. Callbacks must always be in place to receive transfer completion notification. Please see usb_callback_flags(9S) for details on USB callbacks.

Calls made to usb_pipe_intr_xfer() for starting input polling need allocate only one request. The USBA framework allocates a new request each time polling has new data to return. (Note that each request returned must be freed via usb_free_intr_req(9F). Specify a zero length when calling usb_alloc_intr_req() to allocate the original request, since it will not be used to return data. Set the intr_len in the request to specify how much data can be returned per polling interval.

The original request passed to usb_pipe_intr_xfer() is used to return status when polling is terminated, or on an error condition when the USB_ATTRS_AUTOCLEARING attribute is set for the request. If autoclearing is not set, the current (non-original) request is returned on error. Call usb_pipe_reset(9F) to reset the pipe and get back the original request in this case. The USB_CR_STOPPED_POLLING flag is always set for callbacks where the original request is returned.

Single-transfer Interrupt-IN Transfers

Interrupt-IN requests which have the USB_ATTRS_ONE_XFER attribute perform a single transfer. Such requests are synchronous when the USB_FLAGS_SLEEP flag is specified. Calls for synchronous requests do not return until their transaction is complete, and their callbacks are optional. The request is returned to the client through the normal or the exception completion callback to signal either normal completion or an error condition.

Interrupt-OUT Transfers

Interrupt-OUT requests always set up for a single transfer. However, multiple requests can be queued and execute in periodic fashion until depleted.

Interrupt-OUT transfers are synchronous when the USB_FLAGS_SLEEP flag is set in the request's flags. Calls for synchronous transfers will not return until their transaction has completed. Calls for asynchronous transfers notify the client driver of transaction completion via a normal callback, or error completion via an exception callback.

The usb_pipe_stop_intr_polling() function terminates polling on interrupt-IN pipes and does the following:

1. Cease polling.


2. Allow any requests-in-progress to complete and be returned to the client driver through the normal callback mechanism.


3. Idle the pipe.


4. Return the original polling request to the client driver through an exception callback with a completion reason of USB_CR_STOPPED_POLLING.

The client driver may restart polling from an exception callback only if the callback corresponds to an original request. The callback handler checks for the following completion reasons to ensure that a callback corresponds to an original request:

        USB_CR_STOPPED_POLLING,


        USB_CR_PIPE_RESET,


        USB_CR_PIPE_CLOSING,


        USB_CR_NOT_SUPPORTED

The callback handler also checks the request's intr_data field to mark original polling requests, when the requests are created with a zero len argument. In this case, a NULL intr_data field distinguishes a returned original request from a request allocated by the framework during polling.

Mblks for data for interrupt-OUT requests are allocated when a request is allocated via usb_alloc_intr_req(9F) by passing a non-negative value for the len argument.