82801FB Datasheet, PDF (199/786 Pages) Intel Corporation – Intel I/O Controller Hub 6 (ICH6) Family

Functional Description
5.19.8 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 MS-DOS legacy software will not run, because the keyboard will not be identified.
The ICH6 implements a series of trapping operations which will 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 5-9 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 doesn't complete the cycle before the SMI is observed. This
method is used on MPIIX and has been validated.
The logic also needs to block the accesses to the 8042. If there is an external 8042, then this is
simply accomplished by not activating the 8042 CS. This is simply done by logically ANDing the
four enables (60R, 60W, 64R, 64W) with the 4 types of accesses to determine if 8042CS should go
active. An additional term is required for the “pass-through” case.
The state table for Figure 5-9 is shown in Table 5-44.
Figure 5-9. USB Legacy Keyboard Flow Diagram
KBC Accesses
PCI Config
Read, Write
Comb.
Decoder
60 READ
S
D
Clear SMI_60_R
R
EN_SMI_ON_60R
AND
Same for 60W, 64R, 64W
To Individual
"Caused By"
"Bits"
SMI
OR
EN_PIRQD#
AND
To PIRQD#
USB_IRQ
Clear USB_IRQ
S
D
R
EN_SMI_ON_IRQ
AND
To "Caused By" Bit
Intel^® I/O Controller Hub 6 (ICH6) Family Datasheet
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