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Technical Document #107
| Doc ID: |
107 |
| Product: |
WinDriver & KernelDriver |
| Version: |
5.04 - 5.22 |
When performing data transfers with
WD_UsbTransfer(), what is the significance of the USB_SHORT_TRANSFER and USB_FULL_TRANSFER flags (Versions 5.04 - 5.22)?
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These flags are available beginning with version 5.04 of WinDriver.
If the USB_SHORT_TRANSFER flag is set, then WD_UsbTransfer() will return on one of two occasions:
- A short packet (i.e. less than the maximum packet size) was transferred
or the device transferred a zero (0) packet, to indicate a short transfer. In
this case fOk will be TRUE.
- The time-out period (specified in usbTrans.dwTimeout) expired before a short packet was transferred (or a zero packet was received). In this case
fOk will be FALSE.
If the USB_FULL_TRANSFER flag is set, then WD_UsbTransfer() will return on one of the following two occasions:
- The entire buffer (usbTrans.dwBytes) was filled/written. In this case fOk will be
TRUE.
- The time-out period expired before the buffer was entirely filled/written. In this case fOk will be FALSE (although some data may very well have been transferred).
By default, the USB_SHORT_TRANSFER flag is set for bulk and interrupt transfers and the
USB_FULL_TRANSFER flag is set for isochronous transfers. Control transfers are always short transfers.
In former versions of WinDriver (until, and including, v5.03),
WD_UsbTransfer() behaved (for all types of transfers) as described above for the
USB_SHORT_TRANSFER flag in v5.04 and above - i.e. the function always returned on one of two occasions:
- A short packet (i.e. less than the maximum packet size) was transferred
or the device transferred a zero (0) packet, to indicate a short transfer - in
which case fOK would have been
TRUE (even if the buffer was not
entirely filled/written).
- The time-out expired without any such transfer - in which case
fOK would be FALSE.
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