
MOTOROLA
Chapter 8. PCI Bus Interface
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PCI Host and Agent Modes
8.7.2 Accessing the MPC8240 ConTguration Space in Agent Mode
When the MPC8240 is conTgured for agent mode, it responds to PCI conTguration
accesses from external hosts when the MPC8240s IDSEL input signal is asserted. This
allows a remote host access to a subset of the MPC8240s internal conTguration registers.
ConTguring the internal registers of the MPC8240 that are not accessible in agent mode is
described in Section 5.1, òConTguration Register Access.ó
When accessing the MPC8240s conTguration registers, the external host performs the
translation shown in Figure 8-9. The external host uses the appropriate device number to
assert the MPC8240s IDSEL input, and the desired function/register number from 0x00 to
0x47 as described in Section 5.1.5.2, òPCI-Accessible ConTguration Registers.ó
Note that the MPC8240 must not issue PCI conTguration transactions to itself (that is, for
PCI conTguration transactions initiated by the MPC8240, its IDSEL input signal must not
be asserted).
8.7.3 PCI ConTguration Cycle Retry Capability in Agent Mode
When the MPC8240 is conTgured for agent mode and is initializing from ROM located on
the local memory bus, it may be necessary to defer a remote host from completing PCI
conTguration cycles until the local device can be tested and conTgured.
When the MPC8240 RTY_PCI_CFG bit (bit 10 in the PCI arbiter control register) is set,
the MPC8240s PCI bus interface retries PCI conTguration cycles. This mechanism allows
the processor core to complete conTguration of the local memory controller in advance of
a system host controller. Once the MPC8240 has completed local conTguration, it can clear
the RTY_PCI_CFG bit, enabling the system host controller to complete conTguration.
8.7.4 PCI Address Translation Support
The MPC8240 allows remapping PCI memory space transactions to local memory and
processor core transactions to PCI memory space. Note that address translation is supported
only for agent mode; it is not supported when the MPC8240 is operating in host mode. Also
note that since agent mode is supported only for address map B, address translation is
supported only for address map B. The following sections summarize the address
translation support of the MPC8240. See Section 4.3, òAddress Translation,ó for more
detailed information about the MPC8240 address translation facility.
8.7.4.1 Inbound PCI Address Translation
Inbound transactions are PCI memory space accesses initiated by an external PCI master
that are targeted toward the MPC8240. Using inbound address translation, the MPC8240
claims the PCI memory space transaction and translates it to a local memory access. When
the MPC8240 is in agent mode, inbound address translation allows an external PCI master
to access local memory through a window in the PCI memory space.