Peripheral Component Interconnect (Pci) Interface; Pci Bus Arbitration Unit; Address Maps And Translation - Motorola MPC8240 User Manual

Peripheral Logic Overview

1.4.4 Peripheral Component Interconnect (PCI) Interface

The PCI interface for the MPC8240 is compliant with the Peripheral Component
Interconnect Specification Revision 2.1. The PCI interface provides mode-selectable, big-
to little-endian conversion. The MPC8240 provides an interface to the PCI bus running at
speeds up to 66 MHz.
The MPC8240's PCI interface can be configured as host or agent. In host mode, the
interface acts as the main memory controller for the system and responds to all host
memory transactions.
In agent mode, the MPC8240 can be configured to respond to a programmed window of
PCI memory space. A variety of initialization modes are provided to boot the device.

1.4.4.1 PCI Bus Arbitration Unit

The MPC8240 contains a PCI bus arbitration unit, which eliminates the need for an external
unit, thus lowering system complexity and cost. It has the following features:
• Five external arbitration signal pairs. The MPC8240 is the sixth member of the
arbitration pool.
• The bus arbitration unit allows fairness as well as a priority mechanism.
• A two-level round-robin scheme is used in which each device can be programmed
within a pool of a high- or low-priority arbitration. One member of the low-priority
pool is promoted to the high-priority pool. As soon as it is granted the bus, it returns
to the low-priority pool.
• The unit can be disabled to allow a remote arbitration unit to be used.

1.4.4.2 Address Maps and Translation

The MPC8240's processor bus supports memory-mapped accesses. The address space is
divided between memory and PCI according to one of two allowable address maps—map
A and map B. Note that the support of map A is provided for backward compatibility only.
It is strongly recommended that new designs use map B because map A may not be
supported in future devices.
An inbound and outbound PCI address translation mechanism is provided to support the
use of the MPC8240 in agent mode. 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.
When the MPC8240 is configured to be a PCI agent, the amount of local memory visible
to the system is programmable. In addition, it may be necessary to map the local memory
to a different system memory address space. The address translation unit handles the
mapping of both inbound and outbound transactions for these cases.
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