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.
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 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 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 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.
Figure 6. Embedded Systems
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