IDT Tsi310TM, User Manual

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2. Bus Operation 31
Tsi310 User Manual
80B6020_MA001_05
2.2.1.1 PCI to PCI-X Transactions
When the originating bus is operating in the conventional PCI mode and the destination bus is
operating in PCI-X mode, the Tsi310 must buffer memory write transactions from the
conventional PCI interface and count the number of bytes to be forwarded to the PCI-X
interface. If the conventional PCI transaction uses the memory write command and some byte
enables are not asserted, the Tsi310 must use the PCI-X memory write command. If the
conventional PCI command is memory write and all byte enables are asserted, the bridge will
use the memory write PCI-X command. If the conventional transaction uses the memory write
and invalidate command, the bridge uses the PCI-X memory write block command.
The Tsi310 attempts to transfer the write data on the PCI-X interface as soon as the transaction
ends or a 128-byte boundary is crossed, whichever comes first. Writes of greater than 128 bytes
are possible only if more than one 128-byte sector fills up before the write operation is issued on
the PCI-X interface.
2.2.1.2 PCI-X to PCI Transactions
When the originating bus is operating in PCI-X mode and the destination bus is operating in the
conventional PCI mode, the Tsi310 uses the conventional memory write command for both the
PCI-X memory write and PCI-X memory write block commands.
The Tsi310 attempts to transfer write data on the conventional PCI interface when the PCI-X
data crosses a 128-byte boundary or the end of the PCI-X transfer occurs, whichever comes
first. As long as a 128-byte buffer is full, or the end of transfer remains from the PCI-X memory
write command when a 128-byte boundary is crossed, the transfer will continue on the
conventional PCI interface.
2.2.1.3 PCI to PCI Transactions
When both buses are operating in conventional PCI mode, the Tsi310 passes a memory write
command that it receives to the destination interface. However, if command received is a
memory write and invalidate command, the Tsi310 will forward it on to the destination interface
as a memory write command.
The Tsi310 attempts to transfer a memory write command when the transaction ends or a
128-byte boundary is crossed, whichever comes first. As long as a 128-byte buffer is full or the
end of transfer remains from the PCI memory write command when a 128-byte boundary is
crossed, the transfer will continue.