82801DB Datasheet, PDF (172/587 Pages) Intel Corporation – Intel 82801DB I/O Controller Hub 4 (ICH4)

Functional Description
5.16 USB UHCI Controllers (D29:F0, F1 and F2)
The ICH4 contains three USB UHCI Host controllers. Each Host controller includes a root hub
with two separate USB ports each, for a total of 6 USB ports. The ICH4 Host controllers support
the standard Universal Host Controller Interface (UHCI) Specification, Revision 1.1.
• Overcurrent detection on all six USB ports is supported. The overcurrent inputs are 5 V-
tolerant, and can be used as GPIs if not needed.
• The ICH4’s USB UHCI controllers are arbitrated differently than standard PCI devices to
improve arbitration latency.
• The USB UHCI controllers use the Analog Front End (AFE) embedded cell that allows
support for USB High-speed signaling rates, instead of USB I/O buffers.
5.16.1 Data Structures in Main Memory
This section describes the details of the data structures used to communicate control, status, and
data between software and the ICH4: Frame Lists, Transfer Descriptors, and Queue Heads. Frame
Lists are aligned on 4-KB boundaries. Transfer Descriptors and Queue Heads are aligned on
16-byte boundaries.
5.16.1.1 Frame List Pointer
The frame list pointer contains a link pointer to the first data object to be processed in the frame, as
well as the control bits defined in Table 5-56.
Table 5-56. Frame List Pointer Bit Description
Bit
Description
31:4
Frame List Pointer (FLP). This field contains the address of the first data object to be processed in
the frame and corresponds to memory address signals [31:4], respectively.
3:2 Reserved. These bits must be written as 0.
QH/TD Select (Q). This bit indicates to the hardware whether the item referenced by the link pointer
is a TD (Transfer Descriptor) or a QH (Queue Head). This allows the Intel^® ICH4 to perform the proper
1 ^{type of processing on the item after it is fetched.}
0 = TD
1 = QH
Terminate (T). This bit indicates to the ICH4 whether the schedule for this frame has valid entries in
it.
0
0 = Pointer is valid (points to a QH or TD).
1 = Empty Frame (pointer is invalid).
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Intel^® 82801DB ICH4 Datasheet