pi7c8150b Pericom Semiconductor Corporation, pi7c8150b Datasheet - Page 31

• Manufacturer Part Number: pi7c8150b
• Description: Asynchronous 2-port Pci Bridge
• Manufacturer: Pericom Semiconductor Corporation

06-0044
3.7.1
3.7.2
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.
TYPE 0 ACCESS TO PI7C8150B
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
PI7C8150B responds to a Type 0 configuration transaction by asserting P_DEVSEL_L
when the following conditions are met during the address phase:
PI7C8150B 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.
Type 0 configuration write and read transactions do not use data buffers; that is, these
transactions are completed immediately, regardless of the state of the data buffers. The
PI7C8150B ignores all Type 0 transactions initiated on the secondary interface.
TYPE 1 TO TYPE 0 CONVERSION
Type 1 configuration transactions are used specifically for device configuration in a
hierarchical PCI bus system. A PCI-to-PCI bridge is the only type of device that should
respond to a Type 1 configuration command. Type 1 configuration commands are used
when the configuration access is intended for a PCI device that resides on a PCI bus other
than the one where the Type 1 transaction is generated.
PI7C8150B performs a Type 1 to Type 0 translation when the Type 1 transaction is
generated on the primary bus and is intended for a device attached directly to the secondary
bus. PI7C8150B must convert the configuration command to a Type 0 format so that the
secondary bus device can respond to it. Type 1 to Type 0 translations are performed only in
the downstream direction; that is, PI7C8150B generates a Type 0 transaction only on the
secondary bus, and never on the primary bus.
PI7C8150B responds to a Type 1 configuration transaction and translates it into a Type 0
transaction on the secondary bus 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.
Page 31 of 108
ASYNCHRONOUS 2-PORT PCI-TO-PCI BRIDGE
APRIL 2006 – Revision 2.02
PI7C8150B