The Dolphin Express Reflective Memory solution create a reflective memory address space between nodes interconnected with the Dolphin Express DX 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.
Reflective Memory Systems (in computer literature also referred to as mirror memory systems 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.
The solution offers significantly faster access to local data than other solutions from e.g. GE Fanuc. The Dolphin solution uses the computers main memory as reflective memory while other solutions uses expensive device memory. Solutions using main memory benefits 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 DXH adapter comes with two x4 ports that can be used separately or combined into a x8 PCI Express link enabling customer applications to take advantage of the exceptional 20Gb/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 | Latency | Reference |
|---|---|---|---|
| Dolphin DXH x4 | 694 MBytes/s | 1.25us | Dolphin Lab |
| Dolphin DXH x8 | 1330 MBytes/s | 1.25us | 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 |
Dolphin software supports channel bonding of adapters. More than 2352 MBytes/s has been measured using two DXH adapter cards. The latency above is the actual half rount trip time measured by two reflective memory applicaitons running a ping poing pong test.
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 RedHawk Linux available from Concurrent or other CPU shielding techniques / real time operating systems as platform for implementing applications.
The interconnect is highly reliable and based on the standard PCI Express protocols including hardware based CRC checsumming. 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.
The reflective memory functionality is implemented in the Dolphin DXS410 switch. The switch supports up to 10 nodes using x4 PCIe connectins or 5 nodes using x8 PCIe connections and 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 the DXE510 HCA.
The Dolphin Reflective Memory solution is included in the SISCI Developers Kit. The Reflective Memory functionality is available for Linux and Windows. VxWorks optional, please contact Dolphin if this is needed by your project.
Please e-mail pci-support@dolphinics.no for more information and to get the reflective memory enabled drivers.