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authorLinus Torvalds <torvalds@ppc970.osdl.org>2005-04-16 15:20:36 -0700
committerLinus Torvalds <torvalds@ppc970.osdl.org>2005-04-16 15:20:36 -0700
commit1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 (patch)
tree0bba044c4ce775e45a88a51686b5d9f90697ea9d /Documentation/usb/ohci.txt
Linux-2.6.12-rc2
Initial git repository build. I'm not bothering with the full history, even though we have it. We can create a separate "historical" git archive of that later if we want to, and in the meantime it's about 3.2GB when imported into git - space that would just make the early git days unnecessarily complicated, when we don't have a lot of good infrastructure for it. Let it rip!
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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>
+