Flexible & Versatile PCI Express® Switch
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Features
PEX 8508 General Features
o 8-lane PCI Express switch
- Integrated SerDes
o Up to five configurable ports
o 19mm x 19mm, 296-ball PBGA
package
o Typical Power: 1.6 Watts
PEX 8508 Key Features
o Standards Compliant
- PCI Express Base Specification, r1.1
- Standard SHPC Specification, r1.1
(hot-plug)
o High Performance
- Non-blocking internal architecture
- Full line rate on all ports
- Cut-Thru latency: 150ns
o Non-Transparent Bridging
- Configurable Non-Transparent por t
for Multi-Host or Intelligent I/O
Support
o Flexible Configuration
- Five highly flexible & configurable
ports (x1, x2, or x4)
- Configurable with strapping pins,
EEPROM, I2C, or Host software
- Lane and polarity reversal
o PCI Express Power Management
- Link power management states: L0,
L0s, L1, L2/L3 Ready, L2 and L3
- Device states: D0 and D3hot
- Vaux, WAKE#, Beacon support
o Spread Spectrum Clock
- Dual clock domain
o Quality of Service (QoS)
- Two Virtual Channels per port
- Eight Traffic Classes per port
- Fixed and Round-Robin V irtual
Channel Port Arbitration
o Reliability, Availability, Serviceability
- 5 Standard Hot-Plug Controllers
- Upstream port as hot-plug client
- Transaction Layer end-to-end CRC
- Poison bit
- Advanced Error Reporting
- Lane Status bits and GPO ava i l a ble
- Per port error diagnostics
• Bad DLLPs
• Bad TLPs
• CRC errors
- JTAG boundary scan
- Fatal Error out-of-b and signal option
Multi-purpose and Feature Rich PCI Express Switch Family
The ExpressLane™ PEX 8508 device offers PCI Express switching capability
enabling users to add scal abl e high bandwidth, non-blocking interco n nect i on to a
wide variety of applications including intelligent network interface cards, office
automation products, mezzanine cards, servers, storage systems,
communications platforms, laptop docking stations, and embedded-control
products. The PEX 8508 switch can be used as a fan-out or aggregation type
switch, and is equally well-suited to peer-to-peer switching applications.
Highly Flexible Port Configurations
The PEX 8508 offers highly configurable ports. There are a maximum of five ports
and eight lanes that can be con figured to any legal width from x1 to x4, in any
combination to support your specific bandwidth needs. The ports can be symmetric
(each port having the same lane width) or asymmetric (ports having different lane
widths). If you can think of a port/lane combination, you can configure it! Any of
the ports can be designated as the upstream port, and you can even dynamically
change the upstream port.
End-to-end Packet Integrity
The PEX 8508 provides end-to-end CRC protection (ECRC) and Poison bit support
to enable designs that require guaranteed error-free packets. These features are
optional in the PCI Express specificatio n, but PLX provides them across its entire
ExpressLane switch product line.
Non-Transparent “Bridging” in a PCI Express Switch
The PEX 8508 supports full non-transparent bridging (NTB) functionality to allow
implementation of multi-host systems and intelligent I/O modules in applications
such as intelligent adapter cards, processor isolation, and office automation. To
ensure quick product migration, the non-transparency features are implemented in
the same fashion as in standard PCI applications.
Non-transparent bridges allow systems to isolate memory domains by presenting the
processor subsystem as an endpoint, rather than another memory system. Base
address registers are used to translate addresses; doorbell registers are used to send
interrupts between the address domains; and scratchpad registers are accessible from
both address domains to allow inter-processor communication.
Two Virtual Channels
The PEX 8508 switch supports two full-featured Virtual Channe ls (VCs) and eight
Traffic Classes (TCs). The mapping of Traffic Classes to port-specific Virtual
Channels allows for different mappings for different ports. In addition, the devices
offer user-selectable Virtual Channel arbitratio n algorithms to enable us ers to fine
tune the Quality of Service (QoS) required for a specific application.
Low Power with Granular SerDes Control
The PEX 8508 provides low power capability that is compliant with the PCI Express
power management specification. The SerDes physical links can be turned off when
unused for even lower power. Support for Vaux, Wake#, and Beacon allows D3cold
operation and is crucial in such applications as docking stations.
PEX 8508
Version 1.7 2007
Flexible Port Configuration
The lane width for each port can be individually configured
through auto -negotiation, hardware strapping, upstream
software configuration, or through an op tional EEPROM.
The PEX 8508 supports a large number of port configurations.
For example, if you are us ing the PEX 8508 in a fan-out
application, you may configure the upstream port as x4 and
the downstream ports as four x1 ports or two x2. In a peer-to-
peer switch aggregation application you can configure four x2
ports. Figure 1 show most common port conf igurations.
Figure 1. Common Port C on fi gur ations
Hot-Plug for High Availability
Hot plug capability allows users to replace hardware modules
and perform maintenance without powering down th e system.
The PEX 8508 hot-plug capability and Advanced Error
Reporting features makes it suitable for High Availability
(HA) applications. Each port includes a Standard Hot-Plug
Controller. If the PEX 8508 is used in an application where
one or more of its downstream ports connect to PCI Express
slots, each port’s Hot-Plug Controller can be used to manage
the hot-plug event of its associated slot. Furthermore, its
upstream port is a hot-plug client, allowing it to be used on
hot-pluggable adapter cards, backplanes and fabric
modules.
Fully Compliant Power Management
For applications that require power management, the
PEX 8508 devices support both link (L0, L0s, L1, L2/L3
Ready, L2 and L3) and device (D0 and D3hot) power
management states, in compliance with the PCI Express power
management specification. Vaux, Wake# and Beacon support
the wakeup protocol from the D3cold state.
SerDes Power and Signal Management
The PEX 8508 supports software control of the SerDes
outputs to allow optimization of power and signal strength in
a system. The PLX SerDes implementation supports four
levels of power – off, low, typical and high. The SerDes block
also supports loop-back mod es and advanced reporting of
error conditions, which enables efficient debug and
management of the entire system.
Flexible Virtual Channel Arbitration
The PEX 8508 switch supports fixed priority and Round
Robin arbitration schemes for up to two virtual channels. This
allows fine tuning of Quality of Service, efficient use of
packet buffers and the system bandwidth.
Applications
Suitable for host-centric as well as Intelligent I/O applications
the PEX 8508 can be configured for a wide variety of form
factors and applications.
Processor Isolation for Redundancy
The PEX 8508 switch, with its low latency, Hot-Plug, and
NTB capability, allows users to isolate processors in multi-
host or failover applications.
Figure 2. Processor Isolation
Figure 2 shows two server boards. The PCI Express switch is
used to prevent the backup host from enumerating and
configuring portions of the primary host system. In addition,
non transparent ports provide doorbell and mailbox registers
for inter-processor communications. The backup processor
will monitor heartbeat messages from the primary system and
upon failure take over as the primary host.
PEX 8508 has very low latency, under 150ns, to assist in a
rapid failover to the backup system. Here only one PEX 8508
switch is required with the one non transparent port but to
maintain identical board layouts, each board shown has a
PEX 8508 switch. This a p pli cat i on can be generalized to
where each compute or storage or I/O board would include a
PEX 8508 to isolate each processor domain.
Adapter Card Aggregation
The number and variety of PCI Express native-mode devices
is growing quickly. As these devices become mainstream it
will be necessary to create multifunction and multi-port
adapter cards with PCI Express capability.
The PEX 8508 can be used to create an adapter card that
aggregates the PCI Express devices into a single port that can
be plugged into a backplane or a motherboard. Figure 3
shows the PEX 8508 in this application.
Figure 3. Aggregation Adapter Card
The adapter card in Figure 3 is transparent with no local
processor present. Here four Gigabit Ethernet (GE) ports are
aggregated through the switch. Recent MAC/PHY devices for
GE all well as InfiniBand, Fibre Channel, etc., have native
PCI Express support for direct connections to the switch. The
non-blocking low latency design of PEX 8508 provides full
throughput with latency under 150ns.
Intelligent Adapter Card
The PEX 8508 supports the no n-transparency feature. Figure 4
illustrates an intelligent adapter card used in servers and
storage hosts and is commonly used in TCP/IP Offload (TOE)
engines, iSCSI processing, RDMA, or encryption/decryption.
Figure 4. Intelligent Adapter
In this figure, the CPU on the adapter card is isolated from the
host CPU (not shown). The PEX 8508 non-transparent port
allows the two CPUs to be isolated but communicate with
each other through address translation that is integrated into
the PEX 8508. The upstream and downstream as well as the
non-transparent port of the PEX 8508 are fully configurable.
In this adapter, the CPU or other “intellig ent” device with on-
chip processing capability—needs to be isolated from the rest
of the system to avoid memory mapping conflicts.
Office Automation Controller
A low port/lane PCI Express switch can be very useful in a
print engine or similar type system controller in embedded
applications. Such designs require low port/lane counts and
low cost, yet the system throughput can b e very high for
graphics oriented data. Figure 5 shows that the PEX 8508 is
used to transfer data from a scanner and other input devices to
the print engine CPU and back to the marking engine. Many
endpoint devices will b e incorporating native PCI Express
support to allow the use of all fiv e po rts of the PEX 8508.
Complete power management support will reduce system
power consumption. With a small 19mm x 19mm footprint,
the controller board space can be minimized.
Figure 5. Printer Controller Engine
ATCA and XMC Mezzanine Card Applications
The PEX 8508 supports aggr egation or fan-in/out as well as
peer-to-peer switching. Figure 6 shows each I/O Mezzanine
card with a PEX 8508 which can aggregate data to the main
baseboard or allow peer-to-peer switching between I/O
endpoints. Non transparency can isolate each of the I/O
Mezzanine cards from each other.
Figure 6. XMC Mezzanine Card
Software Usage Model
From a system model viewpoint, each PCI Express port is a
virtual PCI to PCI bridge device and has its own set of
PCI Express configuration registers. It is through the upstrea m
port that the BIOS or host can configure the other ports using
standard PCI enumeration. The virtual PCI to PCI bridges
within the PEX 8508 are compliant to the PCI and PCI
Express system models. The Configuration Space Registers
(CSRs) in a virtual primary/se condary PCI to PCI Bridge are
accessible by type 0 configuration cycles through the virtual
primary bus interface (matching bus number, device number,
and function number).
Interrupt Sources/Events
The PEX 8508 switch supports the INTx interrupt message
type (compatible with PCI 2.3 Interrupt signals) or Message
Signaled Inte rrupts (MSI) w h en enabl ed. Interrupt s/ messages
are generated by PEX 8508 for hot-plug events, baseline error
reporting, and advanced error reporting.
Development Tools
PLX is offering hardware and software tools (PEX 8508RDK)
to enable rapid customer design activity. These tools include
the hardware Rapid Development Kit (RDK) and the Software
Development Ki t (SDK).
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RDK
The RDK hardware module includes the PEX 8508 with by
default one upstream x4 port connected to a male-edge
connector, and four downstream x1 ports each connected to a
x16 female slot connector. Third party adapters from x16 to x1
allow the x4 connector to plug into narrower slots. Cards with
larger than x1 connectors can plug into the x16 female
connectors and will auto-negotiate down to x1.
The PEX 8508RDK can be installed in a motherboard, used as
a riser card, or configured as a bench-top board.
The PEX 8508RDK can be used to test and validate customer
software. Additionally, it can be used as an evaluation vehicle
for the PEX 8508 featur es and benefits.
SDK
The SDK tool set includes:
- Linux and Windo ws dri vers
- C/C++ Source code, Objects, libraries
- User’s Guides, Application examples, Tutorials
PLX Technology, Inc.
870 W. Maude Ave.
Sunnyvale, CA 94085 USA
Tel: 1-800-759-3735
Tel: 1-408-774-9060
Fax: 1-408-774-2169
Email: info@plxtech.com
Web: www.plxtech.com
Product Ordering Information
Part Number Description
PEX 8508-AC25BI 8-Lane, 5 Po rt PCIe Switch, 296-ball PBGA 19x19 pkg
PEX 8508-AC 25BI G 8-Lane, 5 Port PCIe Switch, 296-ball PBGA 19x19 pkg, Pb-free
PEX 8508RDK Rapid Development Kit for PEX 8508
Please visit the PLX Web site at http://www.plxtech.com/8508 or contact PLX sales at 408-774-9060 for sampling
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© 2006 PLX Technology, Inc. All rights reserved. PLX and the PLX logo are registered trademarks of PLX Technology, Inc. ExpressLane is a trademark of PLX
Technology, Inc., which may be registered in some jurisdiction. All other product names that appear in this material are for identification purposes only and are
acknowledged to be trademarks or registered trademarks of their respective companies. Information supplied by PLX is believed to be accurate and reliable, but PLX
Technology, Inc. assumes no responsibility for any errors that may appear in this material. PLX Technology, Inc. reserves the right, without notice, to make changes in
product design or specification.
PCI8508-SIL-PB-P1-1.7 05/07
Figure 7. PEX 8508RDK
