82801BA Datasheet, PDF (216/498 Pages) Intel Corporation – Intel 82801BA I/O Controller Hub 2 (ICH2) and Intel 82801BAM I/O Controller Hub 2 Mobile

Functional Description
5.19
5.19.1
Firmware Hub Interface
This section describes the memory cycle type to be used on the Firmware Hub (FWH) interface.
Below are the various types of cycles that are supported by the product.
Cycle Type
FWH Memory Read
FWH Memory Write
Comment
New chip select and addressing are used.
New chip select and addressing are used.
Field Definitions
START
This one clock field indicates the start of a cycle. It is valid on the last clock that LFRAME# is
sampled low. The two start fields that are used for the cycle are shown in the table below. If the
start field that is sampled is not one of these values, then the cycle attempted is not a FWH Memory
Cycle. It may be a valid memory cycle that the FWH component may wish to decode (i.e., it may
be of the LPC memory cycle variety).
AD[3:0]
1101
1110
FWH Memory Read
FWH Memory Write
Indication
IDSEL (Device Select)
This one clock field is used to indicate which FWH component is being selected. The four bits
transmitted over AD[3:0] during this clock are compared with values strapped onto pins on the
FWH component. If there is a match, the FWH component will continue to decode the cycle to
determine which bytes are requested on a read or which bytes to update on a write. If there is not a
match, the FWH component may discard the rest of the cycle and go into a standby power state.
MSIZE (Memory Size)
The value ‘0000b’ is sent in this field. A value of ‘0000b’ corresponds to a single byte transfer.
Other encodings of this field are reserved for future use.
MADDR (Memory Address)
This is a 7-clock field that provides a 28 bit memory address. This allows for up to 256 MB per
memory device, for a total of a 4 GB addressable space. The address is transferred with the most
significant nibble first.
SYNC
The SYNC protocol is the same as described in the LPC specification.
TAR
The TAR fields are the same as described in the LPC specification. Refer to this specification for
further details.
5-154
82801BA ICH2 and 82801BAM ICH2-M Datasheet