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