PI7C7300D datasheet(28/107 Pages) PERICOM

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PI7C7300D

3-PORT PCI-TO-PCI BRIDGE

Page 28 of 107

Pericom Semiconductor

November 2005 - Revision 1.01

Non-prefetchable behavior is used for I/O and configuration read transactions, as well as

for memory read transactions that fall into non-prefetchable memory space.

If extra read transactions could have side effects, for example, when accessing a FIFO,

use non-prefetchable read transactions to those locations. Accordingly, if it is important

to retain the value of the byte enable bits during the data phase, use non-prefetchable

read transactions. If these locations are mapped in memory space, use the memory read

command and map the target into non-prefetchable (memory-mapped I/O) memory space

to use non-prefetching behavior.

4.7.3

READ PREFETCH ADDRESS BOUNDARIES

PI7C7300D imposes internal read address boundaries on read pre-fetched data. When a

read transaction reaches one of these aligned address boundaries, the PI7C7300D stops

pre-fetched data, unless the target signals a target disconnect before the read pre-fetched

boundary is reached. When PI7C7300D finishes transferring this read data to the

initiator, it returns a target disconnect with the last data transfer, unless the initiator

completes the transaction before all pre-fetched read data is delivered. Any leftover pre-

fetched data is discarded.

Prefetchable read transactions in flow-through mode pre-fetch to the nearest aligned 4KB

address boundary, or until the initiator de-asserts FRAME#. Section 4.7.6 describes flow-

through mode during read operations.

PI7C7300D Datasheet(PDF) 28 Page - Pericom Semiconductor Corporation