Freescale Semiconductor MPC5200B - Manual (Page 404)

Overview
MPC5200B Users Guide, Rev. 1
Freescale Semiconductor 12-1
Chapter 12
Universal Serial Bus (USB)
12.1 Overview
The following sections are contained in this document:
• Section 12.2, Data Transfer Types
• Section 12.4, Host Control (HC) Operational Registers , includes:
— Section 12.4.2, Control and Status Partition—MBAR + 0x1000
— Section 12.4.3, Memory Pointer Partition—MBAR + 0x1018
— Section 12.4.4, Frame Counter Partition—MBAR + 0x1034
— Section 12.4.5, Root Hub Partition—MBAR + 0x1048
The Universal Serial Bus (USB) is an external bus standard that supports data transfer rates of 12Mbps. Figure 12-1 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
Figure 12-1. USB Focus Areas
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.
12.2 Data Transfer Types
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