2. PCI Interface
45
PowerSpan II User Manual
80A1010_MA001_09
Integrated Device Technology
www.idt.com
2.
Target-Retry: A termination is requested — by asserting Px_STOP# and Px_DEVSEL# while
Px_TRDY# is high — by the PCI Target because it cannot currently process the transaction. Retry
means the transaction is terminated after the address phase without any data transfer. PowerSpan II
retries read requests while it fetches data from the destination bus. Any attempt by a PCI master to
complete the memory read transaction is retried by the PCI target until at least an 8-byte quantity is
available in the line buffer. If a PCI master does not retry the transaction within 2
15
clocks after a
read request has been latched, the delayed read request latch and line buffer are de-allocated. This
prevents deadlock conditions.
3.
Target-Abort: The PCI target requests a termination of a transaction — by negating Px_DEVSEL#
and Px_TRDY# and asserting Px_STOP# on the same clock edge — when it cannot respond to the
transaction, or during a fatal error. A fatal error occurs when: a bus error is experienced on the
processor bus, the maximum retry count is exceeded, a Target-Abort occurs on the alternate PCI
bus during a read, or a Master-Abort occurs on the alternate PCI bus during a read.
Although there may be a fatal error for the initiating application, the transaction completes
gracefully, ensuring normal PCI operation for other PCI resources. PowerSpan II sets the signaled
Target-Abort (S_TA) bit in the
“PCI-1 Control and Status Register.” on page 251
, and records an
error condition in the event of a Target-Abort (see
)
Error Logging and Interrupts
The PowerSpan II PCI Target records errors under the following conditions:
•
address parity error
•
data parity error on writes
•
Target-Abort
and
“Interrupt Handling” on page 145
for a full description of error
logging support and associated interrupt mapping options.