
PI7C7300
3-PORT PCI-to-PCI BRIDGE
Advanced Information
21
06/04/02 Revision 1.07
4.8
Configuration Transactions
Configuration transactions are used to initialize a PCI system. Every PCI device
has a configuration space that is accessed by configuration commands. All registers
are accessible in configuration space only.
In addition to accepting configuration transactions for initialization of its own
configuration space, the PI7C7300 also forwards configuration transactions for device
initialization in hierarchical PCI systems, as well as for special cycle generation.
To support hierarchical PCI bus systems, two types of configuration transactions are
specified: Type 0 and Type 1.
Type 0 configuration transactions are issued when the intended target resides on the
same PCI bus as the initiator. A Type 0 configuration transaction is identified by the
configuration command and the lowest two bits of the address set to 00b.
Type 1 configuration transactions are issued when the intended target resides on
another PCI bus, or when a special cycle is to be generated on another PCI bus.
A Type 1 configuration command is identified by the configuration command and
the lowest two address bits set to 01b.
The register number is found in both Type 0 and Type 1 formats and gives the
DWORD address of the configuration register to be accessed. The function number is
also included in both Type 0 and Type 1 formats and indicates which function of a
multifunction device is to be accessed. For single-function devices, this value is not
decoded. The addresses of Type 1 configuration transaction include a 5-bit field
designating the device number that identifies the device on the target PCI bus that is to
be accessed. In addition, the bus number in Type 1 transactions specifies the PCI bus
to which the transaction is targeted.
4.8.1
Type 0 Access to PI7C7300
The configuration space is accessed by a Type 0 configuration transaction on
the primary interface. The configuration space cannot be accessed from the secondary
bus.
The
PI7C7300
responds
to
a
Type
0
configuration
transaction
by asserting P_DEVSEL# when the following conditions are met during the address
phase:
§
The bus command is a configuration read or configuration write transaction.
§
Lowest two address bits P_AD[1:0] must be 00b.
§
Signal P_IDSEL must be asserted.
Function code is either 0 for configuration space of S1, or 1 for configuration space of
S2 as PI7C7300 is a multi-function device.
PI7C7300 limits all configuration access to a single DWORD data transfer and returns
target-disconnect with the first data transfer if additional data phases are requested.
Because read transactions to configuration space do not have side effects, all bytes in
the requested DWORD are returned, regardless of the value of the byte enable bits.