[Leapfrog: First Look]
Hark The Arrival Of Advanced Switching
The Merlin Advanced Switching switch builds high-speed fabrics using PCI Express technology.
Enter the critical component for Advanced Switching Interconnect (ASI): The Merlin switch chip forms the centerpiece for StarGen's AXSys family. ASI is based on the PCI Express hardware standard, so the technology will be familiar to designers who already work with PCI Express. PCI Express and AS differ above the physical and link layers. While PCI Express is designed with a single host in mind, ASI assumes a logically connected collection of equal hosts, hence the need for the Merlin.
StarGen's Merlin is a 10-port switch that supports x1, x2, and x4 PCI Express lanes (see the figure). The lanes operate at the usual PCI Express speed of 2.5 Gbits/s. It's also possible to pair up the ports to support an x8 connection. Any mix is possible with the added ability to connect a port to a PCI Express node.
A MATCH MADE IN COMMITTEE PCI Express nodes can't utilize an ASI fabric directly, even though both use the same hardware. Like the Merlin, an ASI switch can implement PI-8 packets. These packets can be used to tunnel other protocols, like PCI Express, between nodes.
PCI Express nodes actually sit in isolation until the ASI fabric is set up before binding a set of PCI Express nodes together. Alternatively, or additionally, PCI Express nodes are accessible via ASI hosts that generate and process PI-8 packets for the PCI Express nodes directly. This standard part of ASI enables ASI systems to take advantage of off-the-shelf PCI Express peripherals.
Chips are usually configured using ASI connections. There also is a low-pin-count (LPC) interface for out-of-band configuration, as well as an option for a serial ROM.
MAKING ASI BOARD DESIGN EASIER StarGen's auto initialization is more sophisticated than most serial fabric implementations. In addition to determining speed and the number of lanes, the Merlin chip checks to see how the lane pins are connected. It also can handle swapped polarity and swapped transmit/receive pairs.
The ability to handle various wiring combinations gives pc-board designers more flexibility. This is especially important when dealing with chips from different sources, which often will be the case with ASI hosts and switches. The Merlin is designed to layout nicely on a pc board, where multiple chips are used to build a switch fabric.
The Merlin virtual channel support includes a pair of ordered channels (OVC), two bypass channels (BVC), and one multicast channel (MVC). There's also a 512-entry multicast address table.
The chip draws only 8 W of power. Its $166 price translates to only $16.60/port. Packaging consists of a dense 31-mm2 BGA.
This could be the year where serial connectivity technologies like Serial ATA, ASI, PCI Express, InfiniBand, and Serial RapidIO really begin to take off. ASI certainly is on its way.
StarGen www.stargen.com
STARGEN MERLIN
Performance: 10 x4 lanes (two can be combined for an x8 connection); also supports x1 and x2 links
Link speed: 2.5 Gbits/s
Fabric throughput: 80 Gbits/s
Maximum packet size: 320 bytes
Features: auto-initialization of each port as an ASI or PCIe port, 215 multicast addresses, PI-8 PCI Express bridging and tunneling support
Latency: 150 ns, unloaded fall-through
Virtual channels: two bypass channels (BVC), two ordered channels (OVC), one multicast channel (MVC), Quality of Service (QoS) manager
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