into a backplane or motherboard. Figure 3 shows the

PEX 8512 in this application.

Quad GE

Quad GE

Quad GE

Quad GE

PEX 8512

PEX 8512

PEX 8512

PEX 8512

x4

x4

x4

x4

x4

x4

x4

x4

x4

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 8512

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 8512 supports the non-transparency feature.

Figure 4 illustrates a host system using an intelligent adapter

card.

I/O

I/O

I/O

I/O

I/O

I/O

I/O

I/O

I/O

I/O

I/O

I/O

I/O

I/O

I/O

I/O

I/O

I/O

I/O

I/O

I/O

I/O

CPU

CPU

CPU

CPU

Intelligent I/O Adaptor

Intelligent I/O Adaptor

Non-Transparent

Port

CPU

Blade

CPU

Blade

Primary

Host

Primary

Host

CPU

Blade

CPU

Blade

CPU

Blade

CPU

Blade

Primary

Host

Primary

Host

x2

x2

x2

x2

x2

x2

x2

x4

x4

I/O

I/O

I/O

I/O

I/O

I/O

I/O

I/O

PEX 8512

PEX 8512

PEX 8512

PEX 8512

NT

PEX 8533

PEX 8533

x2

x2

Figure 4. Intelligent Adapter Usage

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

host CPU. The PEX 8512 non-transparent port allows the two

CPUs to be isolated but communicate with each other through

various registers that are designed in the PEX 8512 for that

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

upstream port and the non-transparent port of PEX 8512

allowing the system to be reconfigured.

Dual Host/Fabric Model

The ExpressLane PEX 8512 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 8512. 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 8512 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

Expansion Application

The PEX 8512 can also be utilized to expand the number of

PCI Express devices in a given system. Figure 6 shows how

the PEX 8512 can be used to double the number of ports

available from the Root Complex. Each port in the PEX 8512

is configured with a x4 link width. The Peer-to-peer

communication feature of the PEX 8512 allows the PCI

Express I/O devices to communicate with each other without

any centralized control.

Root

Complex

Root

Complex

CPU

CPU

PEX 8512

PEX 8512

PEX 8512

PEX 8512

x4

x4

x4

Dual GE

x2

x2

x2

PEX 8512

PEX 8512

PEX 8512

PEX 8512

x4

x4

x4

FC

x4

x4

x4

x4

x4

x4

PCI Express

Slot

PCI Express

PCI Express

Slot

Slot

Dual GE

x2

x2

x2

Dual GE

x2

x2

x2

Dual GE

x2

x2

x2

Figure 6. Expansion Application