82801BA Datasheet, PDF(190/498 Page) Intel Corporation – Intel 82801BA I/O Controller Hub 2 (ICH2) and Intel 82801BAM I/O Controller Hub 2 Mobile

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82801BA Datasheet, PDF (190/498 Pages) Intel Corporation – Intel 82801BA I/O Controller Hub 2 (ICH2) and Intel 82801BAM I/O Controller Hub 2 Mobile

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Functional Description

5.16.8 USB Legacy Keyboard Operation

When a USB keyboard is plugged into the system and a standard keyboard is not, the system may

not boot and DOS legacy software will not run; this is because the keyboard is not identified. The

ICH2 implements a series of trapping operations which snoop accesses that go to the keyboard

controller and put the expected data from the USB keyboard into the keyboard controller.

Note: The scheme described below assumes that the keyboard controller (8042 or equivalent) is on the

LPC bus.

This legacy operation is performed through SMM space.

Figure 5-19 shows the Enable and Status path. The latched SMI source (60R, 60W, 64R, 64W) is

available in the Status Register. Because the enable is after the latch, it is possible to check for

other events that didn't necessarily cause an SMI. It is the software's responsibility to logically

AND the value with the appropriate enable bits.

Note also that the SMI is generated before the PCI cycle completes (e.g., before TRDY# goes

active) to ensure that the processor does not complete the cycle before the SMI is observed. This

method is used on MPIIX and has been validated.

The logic will also need to block the accesses to the 8042. If there is an external 8042, this is

accomplished by not activating the 8042 CS. This is done by logically ANDing the 4 enables

(60R, 60W, 64R, 64W) with the 4 types of accesses to determine if the 8042CS should go active.

An additional term is required for the âPass-throughâ case. The state table for the diagram is shown

in Table 5-75.

Figure 5-19. USB Legacy Keyboard Flow Diagram

KBC Accesses

PCI Config

Read, Write

Comb.

Decoder

60 READ

Clear SMI_60_R

SD

R

EN_SMI_ON_60R

AND

Same for 60W, 64R, 64W

To Individual

"Caused By"

"Bits"

SMI

OR

EN_PIRQD#

AND

USB_IRQ

Clear USB_IRQ

SD

R

EN_SMI_ON_IRQ

AND

To PIRQD#

To "Caused By" Bit

5-128

82801BA ICH2 and 82801BAM ICH2-M Datasheet

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