man pages section 9: DDI and DKI Kernel Functions

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Updated: July 2014



usb_pipe_isoc_xfer, usb_pipe_stop_isoc_polling - USB isochronous transfer and polling functions


#include <sys/usb/usba.h>

int usb_pipe_isoc_xfer(usb_pipe_handle_t pipe_handle, usb_isoc_req_t *request,
     usb_flags_t flags);

void usb_pipe_stop_isoc_polling(usb_pipe_handle_t pipe_handle, usb__flags_t flags);

Interface Level

Solaris DDI specific (Solaris DDI)


For usb_pipe_isoc_xfer():


Isochronous pipe handle on which request is made.


Pointer to isochronous transfer request.


USB_FLAGS_SLEEP is the only flag recognized. Wait for needed resources if unavailable.

For usb_pipe_stop_isoc_polling():


Isochronous pipe handle on which to stop polling for input.


USB_FLAGS_SLEEP is the only flag recognized. Wait for polling to stop.


The usb_pipe_isoc_xfer() function requests the USBA framework to perform a transfer through a USB isochronous pipe. The request is passed to the host controller driver (HCD), which performs the necessary transactions to complete the request.

By their nature, isochronous transfers require several transactions for completion. Each request may contain several packet descriptors. Descriptors correspond to subtransfers to be made in different frames. A request is deemed completed once all packets of that request have been processed. It is illegal to specify the USB_ATTRS_ONE_XFER attribute in an isochronous request. The isochronous polling interval is always one millisecond, the period of a full-speed frame.

All isochronous requests are asynchronous, and will notify the caller of their completion via a callback function. All isochronous requests must specify normal and exception callback handlers.

Requests will wait for needed, unavailable resources when USB_FLAGS_SLEEP has been specified in flags. Requests made without USB_FLAGS_SLEEP set will fail if needed resources are not readily available.

No errors seen during request processing will result in aborted transfers or exception callbacks. Such errors will instead be logged in the packet descriptor's isoc_pkt_status field. These errors can be examined when the completed request is returned through a normal callback.


Allocate room for data when allocating isochronous-OUT requests via usb_alloc_isoc_req(9F), by passing a positive value for the len argument. The data will be divided among the request transactions, each transaction represented by a packet descriptor. (See usb_isoc_request(9F). When all of the data has been sent, regardless of any errors encountered, a normal transfer callback will be made to notify the client driver of completion.

If a request is submitted while other requests are active or queued, and the new request has its USB_ATTRS_ISOC_XFER_ASAP attribute set, the host controller driver will queue the request to start on a frame which immediately follows the last frame of the last queued request.

Isochronous-IN TRANSFERS

All isochronous-IN transfers start background polling, and require only a single (original) request. The USBA framework will allocate a new request each time polling has new data to return. Specify a zero length when calling usb_alloc_isoc_req() to allocate the original request, since it will not be used to return data. Set the isoc_pkts_length in the request to specify how much data to poll per interval (the length of one packet in the request).

The original request passed to usb_pipe_isoc_xfer() will be used to return status when polling termination is requested, or for error condition notification. There can be only one isochronous-IN request submitted at a time.


Isochronous transfer normal-completion callbacks cannot block for any reason since they are called from interrupt context. They will have USB_CB_INTR_CONTEXT set in their callback flags to note this.

Isochronous exception callbacks have the following restrictions for blocking:

  1. They can block for resources (for example to allocate memory).

  2. They cannot block for synchronous completion of a command (for example usb_pipe_close(9F)) done on the same pipe. Asynchronous commands can be started, when the pipe's policy pp_max_async_reqs field is initialized to accommodate them.

  3. They cannot block waiting for another callback to complete.

  4. They cannot block waiting for a synchronous transfer request to complete. They can, however, make an asynchronous request (such as restarting polling with a new isochronous-IN transfer).

Please see the section on callbacks in usb_callback_flags(9S) for more information.

All isochronous transfer exception callbacks signify that polling has stopped. Polling requests are returned with the following completion reasons:


Note: There are no exception callbacks for error conditions.

The usb_pipe_stop_isoc_polling() function terminates polling on an isochronous-IN pipe. The usb_pipe_stop_isoc_polling() function 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.

Return Values

For usb_pipe_isoc_xfer():


Transfer was successful.


Request is NULL.


Called from interrupt context with the USB_FLAGS_SLEEP flag set.


The request has been freed or otherwise invalidated.

A set of conflicting attributes were specified. See usb_isoc_request(9S).

The normal and/or exception callback was NULL, USB_FLAGS_SLEEP was not set and USB_ATTRS_ONE_XFER was not set.

An isochronous request was specified with a zeroed isoc_pkt_descr, a NULL isoc_pkt_descr, or a NULL data argument.

An isochronous request was specified with USB_ATTRS_ISOC_XFER_ASAP and a nonzero isoc_frame_no.


An isochronous request was not specified with one and only one of USB_ATTRS_ISOC_START_FRAME or USB_ATTRS_ISOC_XFER_ASAP specified.

An isochronous request was specified with USB_ATTRS_ISOC_START_FRAME and a zero isoc_frame_no.


An isochronous request was specified with an invalid starting frame number (less than current frame number, or zero) and USB_ATTRS_ISOC_START_FRAME specified.


Pipe handle is NULL or invalid.

Pipe is closing or closed.


Pipe handle refers to a pipe which is in the USB_PIPE_STATE_ERROR state.


Memory, descriptors or other resources unavailable.


Host controller is in error state.


An asynchronous transfer failed or an internal error occurred.

An isoch request requested too much data:
    (length   >  (usb_get_max_pkts_per_isoc_request()  *
     endpoint's  wMaxPacketSize))

The pipe is in an unsuitable state (error, busy, not ready).

Additional status information may be available in the isoc_completion_reason and isoc_cb_flags fields of the request. Please see usb_completion_reason(9S) and usb_callback_flags(9S) for more information.

For usb_pipe_stop_isoc_polling():

None, but will fail if called with USB_FLAGS_SLEEP specified from interrupt context; the pipe handle is invalid, NULL or pertains to a closing or closed pipe; or the pipe is in an error state. Messages regarding these errors will be logged to the console logfile.


Both of these functions may be called from kernel or user context without regard to arguments. May be called from interrupt context only when the USB_FLAGS_SLEEP flag is clear.


/* Start polling on an isochronous-IN pipe. */

    usb_isoc_req_t isoc_req;
    void isoc_pipe_callback(usb_pipe_handle_t, usb_isoc_req_t*);
    void isoc_pipe_exception_callback(
        usb_pipe_handle_t, usb_isoc_req_t*);
    uint_t pkt_size;
    usb_ep_data_t *isoc_ep_tree_node;
    usb_ep_descr_t *isoc_ep_descr = ...;   /* From usb_lookup_ep_data() */

    isoc_ep_descr = &isoc_ep_tree_node->ep_descr;
    pkt_size = isoc_ep_descr->wMaxPacketSize;

    isoc_req = usb_alloc_isoc_req(
        dip, num_pkts, NUM_PKTS * pkt_size, USB_FLAGS_SLEEP);
    isoc_req->isoc_attributes = USB_ATTRS_ISOC_XFER_ASAP;
    isoc_req->isoc_cb         = isoc_pipe_callback;
    isoc_req->isoc_exc_cb     = isoc_pipe_exception_callback;
    isoc_req->isoc_pkts_length  = pkt_size;
    isoc_req->isoc_pkts_count   = NUM_PKTS;
    for (pkt = 0; pkt < NUM_PKTS; pkt++) {
            isoc_req->isoc_pkt_descr[pkt].isoc_pkt_length = pkt_size;

    if ((rval = usb_pipe_isoc_xfer(pipe, isoc_req, USB_FLAGS_NOSLEEP))
        != USB_SUCCESS) {
            cmn_err (CE_WARN,"%s%d: Error starting isochronous pipe polling.",
                ddi_driver_name(dip), ddi_get_instance(dip));


    /* Stop polling before powering off device. Wait for polling to stop. */

    usb_pipe_stop_isoc_polling(pipe, USB_FLAGS_SLEEP);
    pm_idle_component(dip, 0);


See attributes(5) for descriptions of the following attributes:

PCI-based systems
Interface Stability

See Also

attributes(5), usb_alloc_request(9F), usb_get_current_frame_number(9F), usb_get_cfg(9F), usb_get_max_pkts_per_isoc_request(9F), usb_get_status(9F), usb_pipe_bulk_xfer(9F), usb_pipe_ctrl_xfer(9F), usb_pipe_get_state(9F), usb_pipe_intr_xfer(9F), usb_pipe_open(9F), usb_pipe_reset(9F), usb_bulk_request(9S), usb_callback_flags(9S), usb_completion_reason(9S), usb_ctrl_request(9S), usb_ep_descr(9S), usb_intr_request(9S), usb_isoc_request(9S)