Serial RapidIO (SRIO) User's Guide

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1.1.2 RapidIO Interconnect Architecture
HostSubsystem
I/OControlSubsystem
DSP Farm
TDM,GMII,Utopia
CommunicationsSubsystem PCISubsystem
InfiniBand HCA™
ToSystem Area
Network
Memory
Memory
Memory
Memory
RapidIO
RapidIO RapidIO
RapidIO
RapidIO
Backplane
PCI
RapidIO
RapidIO
RapidIO
RapidIO
Switch
Control
Processor
IO
Processor
RapidIOto
InfiniBand
RapidIO
Switch
RapidIO
Switch
Legacy
Comm
Processor
RapidIO
Switch
RapidIOto
PCIBridge
ASIC/FPGA
Memory
Memory
Host
Processor
Host
Processor
DSP DSP DSP DSP
Comm
Processor
1.1.3 Physical Layer 1x/4x LP-Serial Specification
Overview
The interconnect architecture is defined as a packet switched protocol independent of a physical layer
implementation. Figure 2 illustrates the interconnection system.
Figure 2. RapidIO Interconnect Architecture
(1) InfiniBand™ is a trademark of the InfiniBand Trade Association.
Currently, there are two physical layer specifications recognized by the RapidIO Trade Association: 8/16
LP-LVDS and 1x/4x LP-Serial. The 8/16 LP-LVDS specification is a point-to-point synchronous clock
sourcing DDR interface. The 1x/4x LP-Serial specification is a point-to-point, AC coupled, clock recovery
interface. The two physical layer specifications are not compatible.
SRIO complies with the 1x/4x LP-Serial specification. The serializer/deserializer (SERDES) technology in
SRIO also aligns with that specification.
The RapidIO Physical Layer 1x/4x LP-Serial Specification currently covers three frequency points: 1.25,
2.5, and 3.125 Gbps. This defines the total bandwidth of each differential pair of I/O signals. An 8-bit/10-bit
encoding scheme ensures ample data transitions for the clock recovery circuits. Due to the 8-bit/10-bit
encoding overhead, the effective data bandwidth per differential pair is 1.0, 2.0, and 2.5 Gbps
respectively. Serial RapidIO only specifies these rates for both the 1x and 4x ports. A 1x port is defined as
1 TX and 1 RX differential pair. A 4x port is a combination of four of these pairs. This document describes
a 4x RapidIO port that can also be configured as four 1x ports, thus providing a scalable interface capable
of supporting a data bandwidth of 1 to 10 Gbps.
Figure 3 shows how to interface two 1x devices and two 4x devices. Each positive transmit data line (TDx)
on one device is connected to a positive receive data line (RDx) on the other device. Likewise, each
negative transmit data line ( TDx) is connected to a negative receive data line ( RDx).
18 Serial RapidIO (SRIO) SPRUE13A – September 2006
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