3. Processor Bus Interface
85
PowerSpan II User Manual
80A1010_MA001_09
Integrated Device Technology
www.idt.com
3.3.1
Address Phase
The address phase deals with the decoding of processor bus accesses.
3.3.1.1
Transaction Decoding
Transaction decoding on the PB Slave operates in both normal decode mode and Master-based decode
mode.
When PowerSpan II is in normal decode mode, each PB slave monitors the Processor Bus Address
(PB_A[]). When the address falls into one of the programmed windows, and the Transfer Type
(PB_TT[]) is supported, PowerSpan II claims the address tenure.
PB slave image location is controlled by setting the Base Address (BA) field in the
Register Image Base Address Register” on page 295
. PB slave image size is controlled by setting the
Block Size (BS) field in the
“Processor Bus Slave Image x Control Register” on page 287
.
PowerSpan II supports eight general purpose slave images and four specialty slave images. A general
purpose slave image generates memory or I/O reads and writes to the PCI bus. For example, the eight
general purpose slave images can support the local bus traffic of four PowerQUICC II SCCs, two
threads of CPU traffic destined for PCI-1, and two threads destined for PCI-2. The specialty images are
used for the generation of PCI Configuration cycles on PCI-1 and PCI-2, IACK reads on PCI-1, IACK
reads on PCI-2 and PowerSpan II register accesses.
The PB slave image also controls how an incoming PB transaction is mapped to the destination port on
PowerSpan II. For example, there are bits for endian mapping, prefetch behavior, etc.
describes the programming model for a PB Slave Image Control register.
The PB slave image only claims a transaction when all of the following conditions are met:
•
the external address matches the slave image
•
the transaction codes are supported
A PB slave image is defined as the range of processor bus physical address space that
decodes a PowerSpan II access.
“Transaction Decoding” on page 85
), the PB slave image
claims transactions initiated by the PowerSpan II PB Master Interface if the transaction meets
the two conditions listed above. In order to avoid the PB slave from claiming transactions
from the a transaction PowerSpan II PB Master Interface, the Master-based Decode
functionality can be enabled.