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the PCI Bus demystified phần 9

hệ thống khe cắm B bộ phận có thể được sử dụng cho một thẻ ngoại vi. Lưu ý rằng kích thước vật lý của chip cầu nối PCI đưa ra hội đồng quản trị khoảng cầu pallet khe cắm một số. Cấu hình trong slide trước đó có thể dễ dàng mở rộng để chứa một đoạn thứ ba C. | PCI Bus Demystified system slot in Segment B may be used for a peripheral card. Note that the physical size of the PCI bridge chip dictates that the pallet bridge board span several slots. The configuration in the previous slide could be easily extended to accommodate a third Segment C. However the problem with that approach is that transactions targeted at Segment C would have to pass through two bridges incurring latency in each one. It would be preferable to position the host processor so that it could bridge directly to each of the other segments. Figure 9-10 shows a solution to that problem utilizing pallet bridge boards. The host processor resides in the system slot of Segment B and bridges directly to Segments A and C. Note that Segment A must have its system slot on the right and that two different bridge boards are required one that bridges from right to left and another that bridges from left to right. In practice the same PC board can be used for both forms with different mounting locations for the connectors. The same strategy can be implemented with front-loading bridge modules. At least one vendor Teknor currently offers a dual-wide SBC that incorporates the bridge function. Left-hand Bridge Right-hand Bridge Figure 9-10 CPCI bridging of three segments. 164 CompactPCI Summary CompactPCI is an industrial implementation of the PCI bus. It uses a passive backplane and standardized Eurocard mechanics. The use of low-capacitance connectors allows up to eight PCI slots per backplane segment. CompactPCI defines additional signals beyond the basic PCI protocol. Among the features provided by these extra signals are system slot identification system enumeration and geographical addressing. Every board requires series termination of the bus signals. 165 C H A P T E R Hot Plug and Hot Swap In high-availability mission-critical environments it is useful in many cases absolutely essential to be able to swap system components while the system is running. Attempting