USB_ISOC_REQUEST(9S) Data Structures for Drivers USB_ISOC_REQUEST(9S)

usb_isoc_req, usb_isoc_req_t, usb_isoc_request - USB isochronous request structure

#include <sys/usb/usba.h>

illumos DDI specific (illumos DDI)

A request sent through an isochronous pipe is used to transfer large amounts of packetized data with relative unreliability, but with bounded service periods. A packet is guaranteed to be tried within a bounded time period, but is not retried upon failure. Isochronous transfers are supported on both USB 1.1 and USB 2.0 devices. For further information, see section 5.6 of the USB 2.0 specification available at

This section provides information on acceptable combinations of flags and attributes with additional details. The following fields of the usb_isoc_req_t are used to format an isochronous request.


isoc_frame_no; /* frame num to start sending req. */ ushort_t isoc_pkts_count; /* num USB pkts in this request */ /*
* The sum of all pkt lengths in an isoc request. Recommend to set it to
* zero, so the sum of isoc_pkt_length in the isoc_pkt_descr list will be
* used automatically and no check will be apply to this element.
*/ ushort_t isoc_pkts_length; ushort_t isoc_error_count;/* num pkts completed w/errs */ usb_req_attrs_t isoc_attributes;/* request-specific attrs */ mblk_t *isoc_data; /* data to xfer */
/* IN or OUT: alloc. by client. */
/* Size=total of all pkt lengths. */ usb_opaque_t isoc_client_private; /* for client driver excl use. */ struct usb_isoc_pkt_descr /* (see below) */
*isoc_pkt_descr; /*
* Normal callback function, called upon completion.
* This function cannot block as it executes in soft interrupt context.
*/ void (*isoc_cb)(
usb_pipe_handle_t ph, struct usb_isoc_req *req); /* Exception callback function, for error handling. */ void (*isoc_exc_cb)(
usb_pipe_handle_t ph, struct usb_isoc_req *req); usb_cr_t isoc_completion_reason; /* overall completion status */
/* set by USBA framework */
/* See usb_completion_reason(9S) */ usb_cb_flags_t isoc_cb_flags; /* recovery done by callback hndlr */
/* set by USBA on exception. */
/* See usb_callback_flags(9S) */

A usb_isoc_pkt_descr_t describes the status of an isochronous packet transferred within a frame or microframe. The following fields of a usb_isoc_pkt_descr_t packet descriptor are used within an usb_isoc_req_t. The isoc_pkt_length is set by the client driver to the amount of data managed by the packet for input or output. The latter two fields are set by the USBA framework to indicate status. Any packets with an isoc_completion_reason, other than USB_CR_OK, are reflected in the isoc_error_count of the usb_isoc_req_t.

ushort_t isoc_pkt_length; /* number bytes to transfer */
ushort_t isoc_pkt_actual_length; /* actual number transferred */
usb_cr_t isoc_pkt_status; /* completion status */

If two multi-frame isoc requests that both specify the USB_ATTRS_ISOC_XFER_ASAP attribute are scheduled closely together, the first frame of the second request is queued to start after the last frame of the first request.

No stalls are seen in isochronous transfer exception callbacks. Because transfers are not retried upon failure, isochronous transfers continue regardless of errors.

Request attributes define special handling for transfers. The following attributes are valid for isochronous requests:


Start transferring at the starting frame number specified in the isoc_frame_no field of the request.


Start transferring as soon as possible. The USBA framework picks an immediate frame number to map to the starting frame number.


Accept transfers where less data is received than expected.

The usb_isoc_req_t contains an array of descriptors that describe isochronous packets. One isochronous packet is sent per frame or microframe. Because packets that comprise a transfer are sent across consecutive frames or microframes, USB_ATTRS_ONE_XFER is invalid.

See usb_request_attributes(9S) for more information.

Isochronous transfers/requests are subject to the following constraints and caveats:

1) The following table indicates combinations of usb_pipe_isoc_xfer

flags argument and fields of the usb_isoc_req_t request argument
(X = don't care). (Note that attributes considered in this table
some transfer types are characterized by multiple table entries.) Flags Type Attributes Data Semantics --------------------------------------------------------------- X X X NULL illegal X X ONE_XFER X illegal X X ISOC_START_FRAME X illegal
& !ISOC_XFER_ASAP X OUT SHORT_XFER_OK X illegal X IN X !=NULL See table note (A) X X ISOC_START_FRAME !=NULL See table note (B) X X ISOC_XFER_ASAP !=NULL See table note (C) Table notes:
A) continuous polling, new data is returned in
cloned request structures via continuous callbacks,
original request is returned on stop polling
B) invalid if the current_frame number is past
"isoc_frame_no" or "isoc_frame_no" == 0
C)"isoc_frame_no" is ignored. The USBA framework
determines which frame to insert and start
the transfer. 2) USB_FLAGS_SLEEP indicates to wait for resources but
not for completion. 3) For polled reads:
A. The USBA framework accepts a request which
specifies the size and number of packets to fill
with data. The packets get filled one packet per
(1 ms) frame/(125 us) microframe. All requests
have an implicit USB_ATTRS_SHORT_XFER_OK attribute
set, since transfers continue in spite of any en-
countered. The amount of data read per packet will
match the isoc_pkt_length field of the packet
descriptor unless a short transfer occurs. The
actual size is returned in the
isoc_pkt_actual_length field of the packet
descriptor. When all packets of the request have
been processed, a normal callback is done to sig-
nal the completion of the original request.
B. When continuous polling is stopped, the original
request is returned in an exception callback with a
completion reason of USB_CR_STOPPED_POLLING.
(NOTE: Polling can be restarted from an exception
callback corresponding to an original request.
Please see usb_pipe_isoc_xfer(9F) for more information.
C. Callbacks must be specified.
The isoc_completion_reason indicates the status of the transfer. See
usb_completion_reason(9s) for usb_cr_t definitions.
The isoc_cb_flags are set prior to calling the exception
callback handler to summarize recovery actions taken and
errors encountered during recovery. See usb_callback_flags(9s)
for usb_cb_flags_t definitions. --- Callback handling --- All usb request types share the same callback handling. Please see usb_callback_flags(9s) for a description of use and operation.

See attributes(7) for descriptions of the following attributes:

Architecture PCI-based systems
Interface stability Committed

attributes(7), usb_alloc_request(9F), usb_get_current_frame_number(9F), usb_get_max_pkts_per_isoc_request(9F), usb_pipe_bulk_xfer(9F), usb_pipe_ctrl_xfer(9F), usb_pipe_intr_xfer(9F), usb_pipe_isoc_xfer(9F), usb_bulk_request(9S), usb_callback_flags(9S), usb_completion_reason(9S), usb_ctrl_request(9S), usb_intr_request(9S), usb_request_attributes(9S)

April 9, 2016 OmniOS