[linux.git] / Documentation / usb / ohci.txt

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 <[email protected]> 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
  <[email protected]>
Commit	Line	Data
1da177e4 LT	1	23-Aug-2002
	2
	3	The "ohci-hcd" driver is a USB Host Controller Driver (HCD) that is derived
	4	from the "usb-ohci" driver from the 2.4 kernel series. The "usb-ohci" code
	5	was written primarily by Roman Weissgaerber <[email protected]> but with
	6	contributions from many others (read its copyright/licencing header).
	7
	8	It supports the "Open Host Controller Interface" (OHCI), which standardizes
	9	hardware register protocols used to talk to USB 1.1 host controllers. As
	10	compared to the earlier "Universal Host Controller Interface" (UHCI) from
	11	Intel, it pushes more intelligence into the hardware. USB 1.1 controllers
	12	from vendors other than Intel and VIA generally use OHCI.
	13
	14	Changes 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
	23	The "ohci-hcd" driver handles all USB 1.1 transfer types. Transfers of all
	24	types can be queued. That was also true in "usb-ohci", except for interrupt
	25	transfers. Previously, using periods of one frame would risk data loss due
	26	to overhead in IRQ processing. When interrupt transfers are queued, those
	27	risks can be minimized by making sure the hardware always has transfers to
	28	work on while the OS is getting around to the relevant IRQ processing.
	29
	30	- David Brownell
	31	<[email protected]>
	32