CS5535 Datasheet, PDF (95/555 Pages) National Semiconductor (TI) – Geode™ CS5535 I/O Companion Multi-Function South Bridge

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:
1) Device enumeration and configuration.
2) Isochronous data transfers.
3) Asynchronous data transfers.
4) Power management.
5) 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
register-level description of a host controller for the Univer-
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.
USBOPERATIONAL
USBRESET WRITE
USBOPERATIONAL WRITE
USBOPERATIONAL WRITE
USBSUSPEND WRITE
USBRESET WRITE
USBRESUME
USBRESET
USBRESUME WRITE
or
REMOTE WAKEUP
USBSUSPEND
USBRESET WRITE
HARDWARE
RESET
Revision 0.8
SOFTWARE RESET
Figure 4-9. USB Host Controller FSM
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