Reflective Memory
High Speed Low latency reflective memory solution

Dolphin Express reflective memory

Multicast made easy

The Dolphin Express Reflective / reflected memory / Mulitcaset solution create a reflective memory address space between nodes interconnected with the Dolphin Express IX product line. The solution offers significantly higher performance at a much lower cost than other reflective memory solutions and is available both with low cost copper and with long distance fiber as the interconnect. Mixing fiber and copper is fully supported.

 

Broadcast implemented in hardware

Reflective memory systems (in computer literature also referred to as mirror memory systems, replicated shared memory, multicast or replicated memory systems) implements transparent and automatic updates of remote shared memory areas.  Reflective memory is typically mapped into an embedded system application and enables similar applications on other nodes to share updated data without involving any traditional networking protocol and overhead. Data of any size is transmitted to all nodes directly by functionality implemented in hardware.

Typical applications can range from a two-node fail over pair to large DSM applications like aircraft, ship and submarine simulators, automated testing systems, industrial automation and high-speed data acquisition. Because of their inherent replication they are especially good for fault tolerance.

 

Dolphin Express hardware

The reflective memory functionality is implemented in the Dolphin Express IX switches.  Switches  can be cascaded if you need to build larger systems.  You can build a 2 node system without the switch and use the regular data unicast (data only written to single remote memory location, no local updates). All hosts needs to install a Dolphin Express IX adapter card. All nodes can write to the replicated memory simultaneously.  

 

Significantly faster than alternative solutions

The solution offers significantly faster access to local data than other solutions from e.g.  GE Fanuc. The Dolphin multicast solution uses the computer's main memory as reflective memory while other solutions uses expensive device memory.  Solutions using main memory benefit from CPU caching and the very high performance internal memory bus. Device memory on a traditional reflective memory card can not be cached and access to it is very expensive as the CPU needs to fetch the data from the card through the IO system.

The Dolphin IXH adapter comes with a x8 PCI Express link enabling customer applications to take advantage of the exceptional 40Gb/s link bandwidth.

The real measured performance of Dolphin Express reflective memory is listed in the table below. We have also listed published performance data for other solutions.

 

Adapter Bandwidth One way Latency Reference
Dolphin IXH610 x8 - Gen2 - 3 nodes 2005 MBytes/s 0.99us Dolphin Lab
Dolphin IXH610 x8 - Gen2 - 8 nodes 2005 MBytes/s 1.27us Dolphin Lab
GE Fanuc PCI-5579 13.4 MBytes/s NA www.gefanuc.com
GE Fanuc PCIE-5565RC 170 MBytes/s NA www.gefanuc.com

 

The latency above is the actual half round trip time measured by two reflective memory applications running a ping pong test.

 

Deterministic data communication

The fully hardware based memory mapped data transmission does not rely on any operating system service or kernel driver functionality. The solution comes with an extensive software library that makes configuration and setup easy but this software is not in active use during application runtime.

Dolphin recommends the use of RTX (Windows based) from IntervalZero or RedHawk Linux available from Concurrent or other CPU shielding techniques / real time operating systems as platform for implementing hard real-time applications in combination with Dolphin Express reflective memory.

 

High availability

 The interconnect is highly reliable and based on the standard PCI Express protocols including hardware based 32 bit CRC check. The software library comes with functionality to detect PCI Express protocol failures, remote power failures, disconnected cables etc needed to implement a 100% reliable system for ruggedized unfriendly environments.

 

Availability

The Dolphin Reflective Memory solution is included in the SISCI Developers Kit.  The Reflective Memory functionality is available for Linux, RTX and Windows. VxWorks is optional, please contact Dolphin if this is needed by your project.

Please e-mail pci-support@dolphinics.com for more information and to get the reflective memory enabled drivers.