[Product Innovation]
Triple-Port-PCI-To-PCI Bridge Increases Support For System Expansion Slots
This innovative device enhances overall system performance through concurrent bus communication.
Designers building telecom and datacom equipment crave PCI expansion slots. In their minds, more slots mean more line interface cards for their systems. The PCI bus, while restricted in the number of expansion slots it can support, can be easily expanded with one or more PCI-to-PCI bridge chips. The only problem is that standard bridge chips can limit a system's performance.
To address this performance issue, Pericom Semiconductor has come up with a new kind of bridge chip. Instead of designing just another two-port bridge like its competitors, the company decided to add some value. The result was the PI7C7100—a triple-port PCI-to-PCI bridge that integrates two PCI-to-PCI bridges into a single bridge device.
There are definite advantages to having an integrated three-port bridge system rather than two separate dual-port bridges. For example, only one package is needed as opposed to two, saving board real estate. Another bonus is that there's less routing involved. The main benefit, however, is performance (Fig. 1). Here's why.
Consider a system with two bridges. Bridge one connects to secondary bus one and bridge two connects to secondary bus two. Now suppose there are devices on each bus and they want to communicate with one another. A lot of traffic moves from bus one up through the bridge to system memory, which is used as a buffer. From there, data travels back down the primary bus, through the second PCI bridge, and then onto secondary bus two.
It's evident that a lot of traffic goes back and forth unnecessarily on the primary bus just to get the two devices to communicate. To alleviate this, the PI7C7100 offers more than just bus expansion. It also provides a direct link from secondary bus one to bus two through the chip.
In other words, if devices on secondary buses one and two want to communicate, they can do so directly. Avoiding traffic on the primary bus is a performance benefit realized by the new architecture.
The chip is not designed for traditional PCs. In a typical consumer PC, the northbridge chip has enough drive capacity to handle the number of slots needed. Therefore, Pericom is targeting the industrial PC area, which means the server and router markets. These require more and more PCI bridges, due to the fact that most adapters are designed to work with the PCI bus.
Pericom is also focusing on CompactPCI, since this is the platform of choice for the telecom market. The company expects the PI7C7100 to find its way onto CompactPCI CPU cards. Containing a CPU and memory, these cards use a bridge chip to drive the other cards on the passive backplane. The bridge is used as an isolation or extra driver specifically for the slots.
In telecommunications applications, line-interface cards would be connected to the passive backplane (Fig. 1, again). With the exception of the line cards, all components would reside on a single CPU card. On the edge connector of the card are the CompactPCI connectors. The bridge chip interfaces to these and basically provides a buffer between the CPU card and the passive backplane. It's responsible for driving the backplane connectors as well.
Pericom is also targeting proprietary router designs, such as those developed by Cisco, Nortel, Ericcson, and others. These companies leverage existing PCI adapter cards for communications and storage. Another application area is video servers. Manufacturers of these systems generally leverage the market's large number of PCI VGA cards.
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