urb中state成员的取值

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本文详细解释了USB URB（Urban Transfer Request Block）操作中可能出现的各种错误代码及含义，帮助开发者理解并解决USB通信过程中遇到的问题。

from 13.3. USB Urbs: http://www.makelinux.net/ldd3/chp-13-sect-3

Valid values for this variable include:

The urb transfer was successful.

-ENOENT

The urb was stopped by a call to usb_kill_urb.

-ECONNRESET

The urb was unlinked by a call to usb_unlink_urb, and the TRansfer_flags variable of the urb was set to URB_ASYNC_UNLINK.

-EINPROGRESS

The urb is still being processed by the USB host controllers. If your driver ever sees this value, it is a bug in your driver.

-EPROTO

One of the following errors occurred with this urb:

A bitstuff error happened during the transfer.
No response packet was received in time by the hardware.

-EILSEQ

There was a CRC mismatch in the urb transfer.

-EPIPE

The endpoint is now stalled. If the endpoint involved is not a control endpoint, this error can be cleared through a call to the function usb_clear_halt.

-ECOMM

Data was received faster during the transfer than it could be written to system memory. This error value happens only for an IN urb.

-ENOSR

Data could not be retrieved from the system memory during the transfer fast enough to keep up with the requested USB data rate. This error value happens only for an OUT urb.

-EOVERFLOW

A "babble" error happened to the urb. A "babble" error occurs when the endpoint receives more data than the endpoint's specified maximum packet size.

-EREMOTEIO

Occurs only if the URB_SHORT_NOT_OK flag is set in the urb's transfer_flags variable and means that the full amount of data requested by the urb was not received.

-ENODEV

The USB device is now gone from the system.

-EXDEV

Occurs only for a isochronous urb and means that the transfer was only partially completed. In order to determine what was transferred, the driver must look at the individual frame status.

-EINVAL

Something very bad happened with the urb. The USB kernel documentation describes what this value means:

ISO madness, if this happens: Log off and go home

It also can happen if a parameter is incorrectly set in the urb stucture or if an incorrect function parameter in the usb_submit_urb call submitted the urb to the USB core.

-ESHUTDOWN

There was a severe error with the USB host controller driver; it has now been disabled, or the device was disconnected from the system, and the urb was submitted after the device was removed. It can also occur if the configuration was changed for the device, while the urb was submitted to the device.

Generally, the error values -EPROTO, -EILSEQ, and -EOVERFLOW indicate hardware problems with the device, the device firmware, or the cable connecting the device to the computer.