driver-api/usb/URB.rst

1 .. _usb-urb:
6 :Revised: 2000-Dec-05
7 :Again:   2002-Jul-06
8 :Again:   2005-Sep-19
9 :Again:   2017-Mar-29
14     The USB subsystem now has a substantial section at :ref:`usb-hostside-api`
26 - An URB consists of all relevant information to execute any USB transaction
29 - Execution of an URB is inherently an asynchronous operation, i.e. the
33 - Transfers for one URB can be canceled with :c:func:`usb_unlink_urb`
36 - Each URB has a completion handler, which is called after the action
38   context-pointer for passing information to the completion handler.
40 - Each endpoint for a device logically supports a queue of requests.
100 The parameter isoframes specifies the number of isochronous transfer frames
101 you want to schedule. For CTRL/BULK/INT, use 0.  The mem_flags parameter
127 - For ISO there are two startup behaviors: Specified start_frame or ASAP.
128 - For ASAP set ``URB_ISO_ASAP`` in transfer_flags.
141 The ``mem_flags`` parameter, such as ``GFP_ATOMIC``, controls memory
147 - Out of memory (``-ENOMEM``)
148 - Unplugged device (``-ENODEV``)
149 - Stalled endpoint (``-EPIPE``)
150 - Too many queued ISO transfers (``-EAGAIN``)
151 - Too many requested ISO frames (``-EFBIG``)
152 - Invalid INT interval (``-EINVAL``)
153 - More than one packet for INT (``-EINVAL``)
155 After submission, ``urb->status`` is ``-EINPROGRESS``; however, you should
160 multi-buffering, to get seamless ISO streaming.
185 they will get a ``-EPERM`` error.  Thus you can be sure that when
191 cause a memory-access violation.  The driver is responsible for avoiding this,
219 handler, you should have a look at ``urb->status`` to detect any USB errors.
220 Since the context parameter is included in the URB, you can pass
243 have to set ``urb->interval`` to say how often to make transfers; it's
253 The :c:func:`usb_submit_urb` call modifies ``urb->interval`` to the implemented
254 interval value that is less than or equal to the requested interval value.  If
255 ``URB_ISO_ASAP`` scheduling is used, ``urb->start_frame`` is also updated.
283 The :c:func:`usb_submit_urb` call modifies ``urb->interval`` to the implemented
284 interval value that is less than or equal to the requested interval value.