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