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Documentation / usb / ohci.txt




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Based on kernel version 3.13. Page generated on 2014-01-20 22:04 EST.

1	23-Aug-2002
2	
3	The "ohci-hcd" driver is a USB Host Controller Driver (HCD) that is derived
4	from the "usb-ohci" driver from the 2.4 kernel series.  The "usb-ohci" code
5	was written primarily by Roman Weissgaerber <weissg@vienna.at> but with
6	contributions from many others (read its copyright/licencing header).
7	
8	It supports the "Open Host Controller Interface" (OHCI), which standardizes
9	hardware register protocols used to talk to USB 1.1 host controllers.  As
10	compared to the earlier "Universal Host Controller Interface" (UHCI) from
11	Intel, it pushes more intelligence into the hardware.  USB 1.1 controllers
12	from vendors other than Intel and VIA generally use OHCI.
13	
14	Changes since the 2.4 kernel include
15	
16		- improved robustness; bugfixes; and less overhead
17		- supports the updated and simplified usbcore APIs
18		- interrupt transfers can be larger, and can be queued
19		- less code, by using the upper level "hcd" framework
20		- supports some non-PCI implementations of OHCI
21		- ... more
22	
23	The "ohci-hcd" driver handles all USB 1.1 transfer types.  Transfers of all
24	types can be queued.  That was also true in "usb-ohci", except for interrupt
25	transfers.  Previously, using periods of one frame would risk data loss due
26	to overhead in IRQ processing.  When interrupt transfers are queued, those
27	risks can be minimized by making sure the hardware always has transfers to
28	work on while the OS is getting around to the relevant IRQ processing.
29	
30	- David Brownell
31	  <dbrownell@users.sourceforge.net>
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