Universal Serial Bus (USB) Configuration

13.2.6CLASSC–Class Code Register (Function 2)

Address Offset:

0A-0Bh

Default Value:

0C03h

Attribute:

Read only

This register identifies the Base Class Code, Sub-Class Code, and Device Programming interface for IFB PCI Function 2.

Bit

Description

23:16 Base Class Code (BASEC). 0Ch=Serial Bus controller.

15:8 Sub-Class Code (SCC). 03h=USB Host Controller..

7:0 Programming Interface (PI). 00h=Universal Host Controller Interface.

13.2.7MLT–Master Latency Timer Register (Function 2)

Address Offset:

0Dh

Default Value:

00h

Attribute:

Read/Write

MLT is an 8-bit register that controls the amount of time (in terms of PCI clocks) the USB module can do transactions on the PCI bus. The count value is an 8 bit quantity, however MLT[3:0] are reserved and assumed to be 0 when determining the count value. MLT is used when the USB module becomes the PCI bus master and is cleared and suspended when IFB is not asserting FRAME#. When IFB asserts FRAME#, the counter is enabled and begins counting. If the serial bus module finishes its transaction before count is expired, the MLT value is ignored. If the count expires before the transaction completes, IFB initiates a transaction termination as soon as the current transaction is completed.. The number of clocks programmed in the MLT represents the time slice (measured in PCI clocks) allotted to IFB, after which it must surrender the bus as soon as the current transaction is completed.

Bit

Description

7:4 Master Latency Counter Value. IFB initiated PCI cycles (including multiple transactions) can last indefinitely as long as PHLDA# remains active. However, if PHLDA# is negated after a transaction is initiated, IFB limits the duration of the transactions to the number of PCI bus clocks specified by this field.

3:0 Reserved.

13.2.8HEDT–Header Type Register (Function 2)

Address Offset:

0Eh

Default Value:

00h

Attribute:

Read only

This register identifies the Serial Bus module as a single Function device.

Bit

Description

7:0 Device Type (DEVICET). 00. Multi-Function device capability for IFB is defined by the HEDT register in Function 0.

13-4

Intel® 460GX Chipset Software Developer’s Manual