User`s guide

4.1.7.1 PCI Configuration Cycles to Primary Bus Targets
Primary PCI bus devices are selected during a PCI configuration cycle if their
IDSEL# pin is asserted, if the PCI bus command indicates a configuration
read or write transaction, and if ad<1:0> are 00. Bits ad<7:2>, which are
taken from sysAdr<12:7>, select a longword register in the device’s 256-byte
configuration address space. Configuration accesses can use byte masks, which
may be derived by following the method shown in Table 4–4.
Peripherals that integrate multiple functional units (for example, SCSI,
Ethernet, and so on) can provide configuration spaces for each function.
Bits ad<10:8>, which are taken from sysAdr<15:13>, can be decoded by
the peripheral to select one of eight functional units.
Bits <31:11> are used to generate the IDSEL signals. Typically, the IDSEL#
pin of each PCI peripheral is connected to a unique address line. Bits
ad<31:11>, are decoded from sysAdr<20:16> according to Table 4–6, ensuring
that only one bit of ad<31:11> is asserted for any given configuration space
transaction on the primary PCI bus. Bits sysAdr<28:21> are ignored.
4.1.7.2 PCI Configuration Cycles to Secondary Bus Targets
If the PCI cycle is a configuration read or write cycle but ad<1:0> are 01, a
device on a secondary PCI bus is being selected across a PCI-to-PCI bridge.
This cycle will be accepted by a PCI-to-PCI bridge for propagation to its
secondary PCI bus. During this cycle, sysAdr<28:7> generate PCI ad<23:2>,
which has four fields, as listed here:
• ad<23:16>, taken from sysAdr<28:21>, select a unique bus number.
• ad<15:11>, taken from sysAdr<20:16>, select a device on the PCI
(typically decoded by the target bridge to generate IDSEL# signals).
• ad<10:8>, taken from sysAdr<15:13>, select one of eight functional units
per device.
• ad<7:2>, taken from sysAdr<12:7>, select a longword in the device’s
configuration register space.
Each PCI-to-PCI bridge device can be configured using PCI configuration cycles
on its primary PCI interface. Configuration parameters in the PCI-to-PCI
bridge will identify the bus number for its secondary PCI interface and a range
of bus numbers that may exist hierarchically behind it.
4–14 System Address Mapping