2. PCI Interface
44
PowerSpan II User Manual
80A1010_MA001_09
Integrated Device Technology
www.idt.com
The PowerSpan II PCI Target can be configured to keep prefetch data over multiple read accesses for
any master that provides the correct address
—
by setting the PRKEEP bit in the
x Control Register” on page 268
. PowerSpan II increments its latched address for the read transaction
based on the amount of data removed by the PCI master during the read transaction. If the PCI master
returns with an address that matches the incremented address held by PowerSpan II, then PowerSpan II
provides data already held in the prefetch line buffer.
2.2.2.3
Data Parity
PowerSpan II monitors Px_PAR#/Px_PAR64# when it accepts data as a PCI target during a write.
PowerSpan II drives Px_PAR#/Px_PAR64# when it provides data as a PCI target during a read. In both
cases, the Px_PAR#/Px_PAR64# signal provides even parity for Px_C/BE#[3:0] and Px_AD[31:0] —
or Px_C/BE#[7:4] and Px_AD[63:32] for the PCI-1 Interface in 64-bit mode.
“PCI-1 Control and Status Register.” on page 251
determines whether or not
PowerSpan II responds to parity errors as a PCI target. Data parity errors are reported through the
assertion of Px_PERR# when the PERESP bit is set. The Detected Parity Error (D_PE) bit in the
“PCI-1 Control and Status Register.” on page 251
is set when PowerSpan II encounters a parity error as
a PCI target on any transaction. PowerSpan II records an error condition when a parity error occurs (see
).
2.2.3
Termination Phase
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.
2.2.3.1
PCI Target Terminations
The PCI Target Interface generates the following terminations:
1.
Target-Disconnect (with data): A termination is requested by the PCI target — by asserting
Px_STOP# and Px_TRDY# — when it requires a new address phase. Target-Disconnect means the
transaction is terminated after one or more valid data transfers.
The PCI target requests a Target-Disconnect in the following cases:
•
PowerSpan II is unable to buffer an incoming write or provide data from a read buffer during a
read.
•
PowerSpan II reaches the 4-Kbyte address boundary on reads and writes to the processor bus.
•
One data phase for PowerSpan II register accesses
•
One data phase for I
2
O shell accesses
•
Detection of a transaction with non-linear addressing
Writes do not invalidate read buffer contents.