CS5535 datasheet(95/555 Pages) NSC

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USBC Functional Description (Continued)

4.5.4

Host Controller

The USB host interacts with USB devices through the Host

Controller. The host is responsible for:

• Detecting the attachment and removal of USB devices.

• Managing control flow between the host and USB

devices.

• Managing data flow between the host and USB devices.

• Collecting status and activity statistics.

• Providing power to attached USB devices.

The USB system software on the host manages interac-

tions between USB devices and host-based device soft-

ware. There are five areas of interactions between the USB

system software and device software:

Device enumeration and configuration.

Isochronous data transfers.

Asynchronous data transfers.

Power management.

Device and bus management information.

Whenever possible, the USB system software uses existing

host system interfaces to manage the above interactions.

The OHCI specification for the Universal Serial Bus is a

sal Serial Bus, which in turn is described by the Universal

Serial Bus specification. OHCI allows multiple host control-

ler vendors to design and sell host controllers with a com-

mon software interface, freeing them from the burden of

writing and distributing software drivers. The design goal

has been to balance the complexity of the hardware and

software so that OHCI is more than the simplest possible

host controller for USB yet not the most complex possible.

The Host Controller has four USB states visible to the host

controller driver via the operational registers: USBOPERA-

TIONAL

, USBRESET, USBSUSPEND, and USBRESUME. These

states define the Host Controller responsibilities relating to

USB signaling and bus states. The USB states are

reflected in the HostControllerFunctionalState field of the

HcControl register. The Host Controller may only perform a

single state transition. During a remote wakeup event, the

Host Controller may transition from USBSUSPEND to

USBRESUME. The Host Controller interface registers are

PCI memory mapped I/O. The functional state machine

(FSM) is shown in Figure 4-9.

4.5.5

USB Interface

The USB Interface includes the integrated Root Hub with

two external ports, Port 1 and Port 2, as well as the Serial

Interface Engine (SIE) and USB clock generator. The inter-

face combines responsibility for executing bus transactions

requested by the Host Controller as well as the hub and

port management specified by USB.

Figure 4-9. USB Host Controller FSM

USBSUSPEND

USBRESUME

USBOPERATIONAL

USBRESET

USBRESET WRITE

USBOPERATIONAL WRITE

USBRESET WRITE

USBOPERATIONAL WRITE

USBSUSPEND WRITE

USBRESUME WRITE

REMOTE WAKEUP

USBRESET WRITE

HARDWARE

RESET

SOFTWARE RESET

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