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PCIe switches 'first' to integrate DMA engine

Posted: 20 Aug 2008 ?? ?Print Version ?Bookmark and Share

Keywords:integrated DMA engine? PCIe Gen 2 switches? direct memory access?

ExpressLane PEX 8619

PLX Technology Inc. has introduced three PCIe switch devices with innovative architecture that features an integrated direct memory access (DMA) engine. Each switch provides four DMA channels to support the high data rates required in storage systems, servers, networking, control plane and embedded markets. By offloading the DMA function typically required of the processor, PLX's DMA-capable switches increase system performance and create a wide range of new options for next-generation PCIe designs.

The ExpressLane PEX 8619 (16 lanes, 16 ports), PEX 8615 (12 lanes, 12 ports) and PEX 8609 (8 lanes, 8 ports) PCIe Gen 2-compliant switches offer flexible and configurable ports ranging from x1 to x4 on all three devices, with up to x8 on the PEX 8619. The four DMA channels can support high-speed data transfers between I/O devices connected to any of the available ports, while maintaining independence from the unique transparent switch functionality with up to 3Gbit/s throughput per DMA channel. Additional features include a low latency maximum of 140ns and power requirements down to 1.2W typical (8609), with QoS by means of two virtual channels (VCs) per port, spread spectrum clock (SSC) isolation via dual clock domains, and end-to-end guaranteed data integrity.

The DMA engine in these devices implement a descriptor ring approach, while each of the four DMA channels can saturate a x8 link at Gen 2 speeds (up to 4GBps) in one direction. Each descriptor provides support for large transfer sizes (up to 128Mbyte) giving the user the ability to perform very large data transfers in any direction (memory to device, device to device, memory to memory). Descriptors can exist in host memory or, alternatively, inside the DMA switch. Up to 256 descriptors are supported internally in PLX DMA switches, which also support 32bit and 64bit transfers as well as programmable QoS.

"By allowing processors to focus on computational tasks instead of managing the constant delays required of DMA functionality, PLX's new switch technology offers the opportunity to take up this slack in system latency while delivering a scalable, high-bandwidth, non-blocking Gen 2 performance interconnection," said Krishna Mallampati, senior product marketing manager, PLX. "As PCIe switches have become a fundamental building block in today's designs, these feature-rich PLX chips can help in preliminary architectural considerations."

Each switch provides four DMA channels to support the high data rates in systems.

The PEX 8619, PEX 8615 and PEX 8609 volume prices are $28.55, $22.25 and $14.25, respectively, and will be sampling in Q4 08, with full production delivery slated for Q1 09. PLX's PCIe switches provide board and system designers with the industry's most extensive and proven lineup of products ranging in density from three to 16 ports and from 4 to 48 lanes.

Meanwhile, PLX will be hosting a Gen 2 switch product demonstration showcasing its production-ready devices at the Intel Developer Forum this week (Aug. 19-21).

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