feature. Figure 3 illustrates a dual host system with an active

and standby processor configuration. The redundancy of the

host and the fabric can be achieved through the NTB function

of PEX 8609. Additionally, the DMA engine in the PEX8609

can be used to mirror the data on both the active and standby

hosts.

Figure 3. Active-Standby Failover

DMA in Control Planes

The DMA engine in the PEX8609 can alternatively be used to

perform housekeeping tasks, such as reading device status

information from the many endpoints available. This

particular usage model allows the DMA engine to perform the

many data transfers for endpoint status that would otherwise

be handled by the processor.

Figure 4. PEX8609 DMA in a Packet Router

Distributed Computing

The PEX 8609 is well suited for distributed computing

applications. Once programmed, the DMA engine in the

PEX8609 transfers the data between servers and through the

NT port at a high rate. The processor can focus all of its

computing cycles manipulating the large amounts of data

received.

Figure 5. Distributed Computing

Intelligent Adapter Card Redundancy

The PEX 8609 supports the non-transparency feature.

Figure 6 illustrates a host system using an intelligent adapter

card.

Figure 6. Intelligent Adapter Usage

In this figure, the CPU on the adapter card is isolated from the

host CPU. The PEX 8609 non-transparent port allows the two

CPUs to be isolated but communicate with each other through

various registers that are designed in the PEX 8609 for that

purpose. Moreover, the internal DMA engine can be used to

copy or mirror the data between adapter cards so that

intelligent I/O adapter redundancy is achieved.

This model can be expanded to an Active-Standby failover

model. In this case, there is an Active host and a Standby host

ready to take over the system in the event the Active host fails.

The DMA engine in the PEX8609 can be used to mirror the

data between hosts thus minimizing the failover time.

Generic Data Mover

The DMA engine in the PEX8609 is very flexible. It

implements Four DMA channels capable of saturating a x8

Gen2 PCI Express link. Furthermore, it supports a Descriptor

Ring approach in which the descriptors can be placed in

external host memory or internal to the PEX8609. The DMA

engine can move data from any port to any port including the

same port. That is, the source and destination for a DMA

transfer can be on the same PEX8609 port. Figure 7 shows

two PCIe endpoints and a PEX8609 device connected through

a PCIe switch. In this example, one PCIe endpoint behind the

PEX8609 takes advantage of the DMA capabilities in the

PEX8609 to move data from PCIe2 to PCIe1.

Figure 7. Generic Data Mover