Intel CONTROLLERS 413808 - Manual (Page 490)

Intel
®
413808 and 413812—System Controller (SC) and Internal Bus Bridge
Intel ® 413808 and 413812 I/O Controllers in TPER Mode
Developer’s Manual October 2007
490 Order Number: 317805-001US
7.3 Internal Bus Bridge
This section describes the internal bus bridge. The internal bus bridge isolates traffic on
the north internal bus and the south internal bus. The internal bus bridge is a
bidirectional bridge. Transactions targeting the south internal bus from the north
internal bus are referred to as
outbound transactions
. Transactions targeting the
north internal bus from the south internal bus are referred to as
inbound
transactions
.
7.3.1 Theory of Operation
The bridge forwards north internal bus address requests that are not claimed on the
north internal bus. For example, the bridge performs subtractive decoding on the north
internal bus interface. The bridge claims and forwards a north internal bus data
transaction when the ID provided with the data transaction matches the ID of a
previously claimed write address request.
On the south internal bus, the XBG defines a Bridge Memory Window. Transactions on
the south internal bus that target the Bridge Memory Window are claimed and
forwarded to the north internal bus. The bridge claims and forwards a south internal
bus data transaction when the ID provided with the data transaction matches the ID of
a previously claimed write address request. The Bridge south interface also claims
transactions that target the Bridge memory-mapped registers. Intel XScale
®
processor
transactions that target the Bridge memory-mapped registers are also propagated to
the south internal bus, and then claimed by the Bridge south interface.
Both the north and south internal busses on 4138xx support the same bus protocol.
The internal bus operates by performing split transactions on both read and write
address requests. Every address request contains an Address Transfer ID (ATID), which
is the ID of the initiator. Every initiator has a unique ATID. When an initiator makes a
read request, it drives its ATID along with the address request. Once the Bridge claims
the request, it maintains the ATID, which it uses when returning read completion data
in the form of a Data Transfer ID (DTID). The initiator of the read request claims the
read completion transaction by observing that the DTID matches its ATID. For a write
request, the initiator drives its ATID along with the address request. Once the Bridge
claims the request, it maintains the ATID, which it uses to claim a data transaction. The
initiator of the write request drives a Data Transfer ID (DTID) with the data transaction.
The Bridge claims the data transaction by observing that the DTID matches the stored
ATID.
Each of the initiator/requester on the 4138xx has an assigned unique ID, which helps
identify an initiator when returning read data and for the purpose of logging transaction
errors. Table 329 lists the encoded initiator IDs. The bridge uses the same initiator ID
of a transaction it claims when forwarding the transaction on the opposite internal bus.