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