Freescale Semiconductor MPC5200B ユーザーズマニュアル

Freescale Semiconductor

12-1

The following sections are contained in this document:

•

•

, includes:

—

—

—

—

The Universal Serial Bus (USB) is an external bus standard that supports data transfer rates of 12Mbps. 

 shows the four main 

areas of a USB system, which are:

•

Client software/USB driver—software implemented

•

Host Controller Driver (HCD)—software implemented

•

Host Controller (HC)—hardware implemented

•

USB device—hardware implemented

The Open Host Controller Interface (OHCI) is a register-level description of a HC for the Universal Serial Bus (USB). OHCI specifies the 
interface between and the fundamental HCD operation and the HC.

The HCD and HC work in tandem to transfer data between client software and a USB device. Data is translated from shared-memory data 
structures at the client software end, to USB signal protocols at the USB device end, and vice-versa.

Four data transfer types are defined in the USB. Each type is optimized to match the service requirements between client software and the 
USB device. These types are:

•

Interrupt Transfers—Small data transfers used to communicate information from the USB device to the client software. The HCD 
polls the USB device by issuing tokens to the device at a periodic interval sufficient for the requirements of the device.

•

Isochronous Transfers—Periodic data transfers with a constant data rate. Data transfers are correlated in time between the sender 
and receiver.

•

Control Transfers—Non-periodic data transfers used to communicate configuration/command/status type information between 
client software and the USB device.

Software

Hardware

Host Controller

Client Software

USB Driver

Host Controller Driver

USB Device

Scope of OHCI