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IDT PCI Bus Interface
PCI Target
79RC32438 User Reference Manual
10 - 37
November 4, 2002
Notes
I/O Write
PCI I/O write transactions that map to a PCI Base Address (PBAx) register are converted to local IPBus
write operations and posted to the PCI target input FIFO. PCI I/O write transactions are posted to the PCI
target input FIFO and are not allowed to burst.
Memory Read
PCI memory read transactions that map to a PCI Base Address (PBAx) register are mapped to local
IPBus read operation(s). The behavior of PCI target memory read operations is determined by the state of
the Memory Read Behavior (MR) field in the corresponding PBAxC register. If MR field is 0x0, the memory
read behaves as described below. If the MR field is 0x1, the memory read transaction behaves in the same
manner as a memory read line transaction. If the MR field is 0x2, the memory read transaction behaves in
the same manner as a memory read multiple transaction.
PCI memory read transactions that map to a PCI Base Address (PBAx) register are mapped to a local
IPBus word read operation. PCI memory read transactions are not allowed to burst unless the memory read
is mapped to a memory read line or memory read multiple.
Memory Write
PCI memory write transactions that map to a PCI Base Address (PBAx) register are mapped to a local
IPBus write operation(s) and posted into the PCI target input FIFO. The PCI bus interface will attempt to
extend memory write burst transaction for as long as possible. A burst transaction will be retried by the
RC32438 if the PCI target input FIFO is full for a period of time which exceeds the programmed RTIMER/
DTIMER value in the PCITC register.
Configuration Read
PCI configuration read transactions return the value of the register in PCI configuration space with
address PCIAD[7:2]. The PCI bus interface does not support target burst configuration read transactions. If
a configuration read transaction consists of more than a single data phase, the target will terminate the
transaction with a disconnect.
Configuration Write
PCI configuration write transactions return the value of the register in PCI configuration space with
address PCIAD[7:2]. The PCI bus interface will use the byte enables to determine which bytes of the word
address by PCIAD[7:2] are being modified. The PCI bus interface does not support target burst configura-
tion write transaction. If a configuration write transaction consists of more than a single data phase, the
target will terminate the transaction with a disconnect.
Memory Read Multiple
PCI memory read multiple transactions that map to a PCI Base Address (PBAx) register are mapped to
local IPBus read operations. Memory read multiple transactions fetch not only the data requested by the
data phase of the transaction but cause the PCI bus interface to prefetch additional data. The prefetching
behavior is controlled by the Memory Read Multiple Prefetching Behavior (MRM) bit. If cleared, the PCI bus
interface performs conservative prefetching. Otherwise, the PCI bus interface performs aggressive
prefetching.
In conservative prefetching, the PCI bus interface will prefetch 16 words whenever a memory read
multiple transaction is in progress and there are less than 8 words available in the PCI target output FIFO.
In aggressive prefetching, the PCI bus interface will continue prefetching bursts of 16 words as long as
room exists in the PCI target output FIFO. The PCI target output FIFO will discard prefetched data in the
FIFO when a memory read line multiple burst transaction completes.