1 ==== 2 OHCI 3 ==== 4 5 23-Aug-2002 6 7 The "ohci-hcd" driver is a USB Host Controller Driver (HCD) that is derived 8 from the "usb-ohci" driver from the 2.4 kernel series. The "usb-ohci" code 9 was written primarily by Roman Weissgaerber <weissg@vienna.at> but with 10 contributions from many others (read its copyright/licencing header). 11 12 It supports the "Open Host Controller Interface" (OHCI), which standardizes 13 hardware register protocols used to talk to USB 1.1 host controllers. As 14 compared to the earlier "Universal Host Controller Interface" (UHCI) from 15 Intel, it pushes more intelligence into the hardware. USB 1.1 controllers 16 from vendors other than Intel and VIA generally use OHCI. 17 18 Changes since the 2.4 kernel include 19 20 - improved robustness; bugfixes; and less overhead 21 - supports the updated and simplified usbcore APIs 22 - interrupt transfers can be larger, and can be queued 23 - less code, by using the upper level "hcd" framework 24 - supports some non-PCI implementations of OHCI 25 - ... more 26 27 The "ohci-hcd" driver handles all USB 1.1 transfer types. Transfers of all 28 types can be queued. That was also true in "usb-ohci", except for interrupt 29 transfers. Previously, using periods of one frame would risk data loss due 30 to overhead in IRQ processing. When interrupt transfers are queued, those 31 risks can be minimized by making sure the hardware always has transfers to 32 work on while the OS is getting around to the relevant IRQ processing. 33 34 - David Brownell 35 <dbrownell@users.sourceforge.net>
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