ohci.rst 1.5 KB

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