adapter cards with PCI Express capability. The PEX 8518 can

be used to create an adapter or mezzanine card that aggregates

the PCI Express devices into a single port that can be plugged

into a backplane or motherboard. Figure 3 shows the

PEX 8518 in this application.

Figure 3. Aggregation Adapter Card

The adapter card in Figure 3 can be transparent, in which

case the PCI Express I/O devices are just standard I/O

endpoints such as Ethernet or Fibre Channel. Or the PEX 8518

can provide a non-transparent port to the system (via the

card’s edge connector). In this case, one of the PCI Express

devices can be a CPU or other “intelligent” device with on-

chip processing capability – thus needing address domain

isolation from the rest of the system. This approach is

commonly used in RAID controllers.

Intelligent Adapter Card

The PEX 8518 supports the non-transparency feature.

Figure 4 illustrates a host system using an intelligent adapter

card.

Figure 4. Intelligent Adapter Usage

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

host CPU. The PEX 8518 non-transparent port allows the two

CPUs to be isolated but communicate with each other through

various registers that are designed in the PEX 8518 for that

purpose. The host CPU can dynamically re-assign both the

upstream port and the non-transparent port of PEX 8518

allowing the system to be reconfigured.

Dual Host/Fabric Model

The ExpressLane PEX 8518 supports applications requiring

dual host, host failover, and load-sharing applications

through the non-transparency feature. Figure 5 illustrates a

dual host system with dual switch fabric in dual-star

configuration.

The redundancy of the host and the fabric can be achieved

through many possible configurations using NTB function of

PEX 8518. In the configuration shown below the host 1

controls the switch 1 and associated I/Os and the host 2

controls the switch 2 and associated I/Os. The hosts and

switches are isolated using NTB functionality of PEX 8518 on

the host boards. If one of the hosts fails the surviving host can

remove the failing host from the configuration while

controlling both the switches and all I/Os. Similarly, if one of

the switches fails the host associated with that switch can send

control messages to its I/Os through the surviving switch using

NTB function.

Figure 5. Dual Host/Fabric Mode

Embedded Systems

The PEX 8518 can also be utilized in embedded applications.

Figure 6 shows several independent modules connecting

through the PEX 8518. The port widths for each module can

be configured as required. The Peer-to-peer communication

feature of the PEX 8518 allows these modules to communicate

with each other without any centralized control.

Figure 6. Embedded Systems