A host controller interface (HCI) is a register-level
interface that enables a
host controller for
USB or
IEEE 1394 hardware to communicate with a host controller driver in software. The driver software is typically provided with an
operating system of a
personal computer, but may also be implemented by application-specific devices such as a
microcontroller
A microcontroller (MCU for ''microcontroller unit'', often also MC, UC, or μC) is a small computer on a single VLSI integrated circuit (IC) chip. A microcontroller contains one or more CPUs (processor cores) along with memory and programmable i ...
.
On the
expansion card or motherboard controller, this involves much custom logic, with digital logic engines in the motherboard's controller chip, plus analog circuitry managing the high-speed differential signals. On the
software side, it requires a
device driver
In computing, a device driver is a computer program that operates or controls a particular type of device that is attached to a computer or automaton. A driver provides a software interface to hardware devices, enabling operating systems and ot ...
(called a Host Controller Driver, or HCD).
IEEE 1394
Open Host Controller Interface
Open Host Controller Interface (OHCI)
[http://download.microsoft.com/download/1/6/1/161ba512-40e2-4cc9-843a-923143f3456c/ohci_11.pdf ] is an
open standard
An open standard is a standard that is openly accessible and usable by anyone. It is also a prerequisite to use open license, non-discrimination and extensibility. Typically, anybody can participate in the development. There is no single definition ...
.
When applied to an
IEEE 1394 (also known as
FireWire
IEEE 1394 is an interface standard for a serial bus for high-speed communications and isochronous real-time data transfer. It was developed in the late 1980s and early 1990s by Apple in cooperation with a number of companies, primarily Sony an ...
;
i.LINK or Lynx) card, OHCI means that the card supports a standard interface to the PC and can be used by the OHCI IEEE 1394 drivers that come with all modern
operating systems. Because the card has a standard OHCI interface, the OS does not need to know in advance exactly who makes the card or how it works; it can safely assume that the card understands the set of well-defined commands that are defined in the standard
protocol
Protocol may refer to:
Sociology and politics
* Protocol (politics), a formal agreement between nation states
* Protocol (diplomacy), the etiquette of diplomacy and affairs of state
* Etiquette, a code of personal behavior
Science and technology
...
.
USB
Open Host Controller Interface
The OHCI standard for
USB is similar to the OHCI standard for IEEE 1394, but supports USB 1.1 (full and low speeds) only; so as a result its register interface looks completely different. Compared with UHCI, it moves more intelligence into the controller, and thus is accordingly much more efficient; this was part of the motivation for defining it. If a computer provides non-x86 USB 1.1, or x86 USB 1.1 from a USB controller that is not made by Intel or VIA, it probably uses OHCI (e.g. OHCI is common on add-in PCI Cards based on an NEC chipset). It has many fewer intellectual property restrictions than UHCI.
It only supports 32-bit memory addressing,
so it requires an
IOMMU or a computationally expensive
bounce buffer
In computer science, multiple buffering is the use of more than one buffer to hold a block of data, so that a "reader" will see a complete (though perhaps old) version of the data, rather than a partially updated version of the data being create ...
to work with a 64-bit operating system . OHCI interfaces to the rest of the computer only with
memory-mapped I/O.
Universal Host Controller Interface
Universal Host Controller Interface (UHCI) is a