2. PCI Interface
37
PowerSpan II User Manual
80A1010_MA001_09
Integrated Device Technology
www.idt.com
2.2
PCI Target Interface
PowerSpan II participates in a transaction as a PCI target when a PCI master initiates one of the
following actions:
•
attempts to access the alternate PCI Interface
•
attempts to access processor bus memory
•
accesses PowerSpan II registers
This chapter describes only the first two conditions listed above. Transactions targeted for the
PowerSpan II’s 4 Kbytes of device control and status registers are discussed in
.
The operation of the PCI Target is described by dividing the PCI transaction into the following phases:
•
Address phase: This section discusses the decoding of PCI accesses.
•
Data phase: This section describes control of burst length and byte lane management.
•
Terminations: This section describes the terminations supported by the PowerSpan II, how they are
mapped from the destination port to the PCI Target, and exception handling.
2.2.1
Address Phase
The address phase deals with the decoding of PCI accesses.
2.2.1.1
Transaction Decoding
Transaction decoding on the PCI Target operates in both normal decode mode and Master-based
decode mode. Only memory and configuration cycles are decoded. I/O cycles are not decoded.
During normal decode mode, a PCI device monitors the Px_AD and Px_C/BE# lines to decode an
access to some programmed PCI physical address range
—
through positive decoding.
A PCI target image is defined as the range of PCI physical address space to decode a PCI transaction. A
PCI target image location and size is controlled using a Base Address field and in the
, and a Block Size field in the
“PCI-1 Target Image x Control Register”
Normal address decoding only applies to memory cycles.