| Mauro Carvalho Chehab | d80b500 | 2019-04-15 23:56:01 -0300 | [diff] [blame] | 1 | ==== |
| 2 | OHCI |
| 3 | ==== |
| 4 | |
| Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 5 | 23-Aug-2002 |
| 6 | |
| 7 | The "ohci-hcd" driver is a USB Host Controller Driver (HCD) that is derived |
| 8 | from the "usb-ohci" driver from the 2.4 kernel series. The "usb-ohci" code |
| 9 | was written primarily by Roman Weissgaerber <weissg@vienna.at> but with |
| 10 | contributions from many others (read its copyright/licencing header). |
| 11 | |
| 12 | It supports the "Open Host Controller Interface" (OHCI), which standardizes |
| 13 | hardware register protocols used to talk to USB 1.1 host controllers. As |
| 14 | compared to the earlier "Universal Host Controller Interface" (UHCI) from |
| 15 | Intel, it pushes more intelligence into the hardware. USB 1.1 controllers |
| 16 | from vendors other than Intel and VIA generally use OHCI. |
| 17 | |
| 18 | Changes since the 2.4 kernel include |
| 19 | |
| 20 | - improved robustness; bugfixes; and less overhead |
| 21 | - supports the updated and simplified usbcore APIs |
| 22 | - interrupt transfers can be larger, and can be queued |
| 23 | - less code, by using the upper level "hcd" framework |
| 24 | - supports some non-PCI implementations of OHCI |
| 25 | - ... more |
| 26 | |
| 27 | The "ohci-hcd" driver handles all USB 1.1 transfer types. Transfers of all |
| 28 | types can be queued. That was also true in "usb-ohci", except for interrupt |
| 29 | transfers. Previously, using periods of one frame would risk data loss due |
| 30 | to overhead in IRQ processing. When interrupt transfers are queued, those |
| 31 | risks can be minimized by making sure the hardware always has transfers to |
| 32 | work on while the OS is getting around to the relevant IRQ processing. |
| 33 | |
| 34 | - David Brownell |
| 35 | <dbrownell@users.sourceforge.net> |