Crossbar switch in multiprocessor system

 

Different schemes of interconnection structure are:

Crossbar Switch

The crossbar switch organization consists of a number of cross points that are placed at intersections between processor buses and memory module paths. Figure below shows a crossbar switch interconnection between four CPUs and four memory modules. The small square in each cross point is a switch that determines the path from a processor to a memory module. Each switch point has control logic to set up the transfer path between a processor and memory. It examines the address that is placed in the bus to determine whether its particular module is being addressed. It also resolves multiple requests for access to the same memory module on a predetermined priority basis.

Figure : Structure of Crossbar Switch

The circuit consists of multiplexers that select the data address, and control from one CPU for communication with the memory module. Priority levels are established by the arbitration logic to select one CPU, when two or more CPUs attempt to access the same memory.

Figure : Block Diagram of Multiplexers and Arbitration Logic

Advantages

Support simultaneous transfer from memory modules.

It provides full connectivity.

Highly useful in multiprocessor system.

Maximum use of bandwidth compares to other networks.

Disadvantages

Number of cross-point = N2 (N - Square)

Complex hardware requirement.

Vulnerable to single fault.

To learn more about Crossbar switch, watch below video

Video : Crossbar switch

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