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Crossbar ASIC

The crossbar ASIC is yet another part of the sx1000 Chipset. It implements a high-performance 8-port non-blocking crossbar and the 500 MHz crossbar link protocol. All ports are functionally and electrically identical. The Integrity Superdome fabric is a fully connected crossbar mesh with four pairs of crossbar ASICs and four cells per crossbar ASIC pair. Like the cell controller ASIC, the crossbar ASIC has truly impressive scale. HP believes that it also is one of the world’s largest ASICs, with 18 million transistors and six layers of metal, using copper technology.

A very important aspect of the crossbar mesh is that all links have the same bandwidth and latency, which is key to increasing overall bandwidth and reducing overall latency. Cell-to-crossbar and crossbar-to-crossbar communication occur at the same speed—there are no excessive latency penalties for going remote. In addition, the server’s memory interleaves across cells first, then across memory banks. This interleaving scheme tends to balance out memory traffic across all the links.

The crossbar mesh implements a global point-to-point packet filtering network. This mesh features an extremely high level of integrity, with each crossbar port fully independent. The crossbar mesh has dedicated paths for data and control. Each port can be reset, assigned, or reconfigured fully independent of other ports. The server’s crossbar mesh is an excellent foundation for resource isolation.

The crossbar ASIC offers several features that contribute to the high performance of the HP Integrity Superdome:

  • Support for scaling up to a 128-way coherent shared memory system (with Intel Itanium 2 and PA-8800 processors, mx2 Dual-Processor Modules, and future PA-RISC [PA-8900] and Intel Itanium 2 processors)

  • 250 MHz operation

  • 500 mega transfers/second (MT/s) link speed

  • Support for two interleaved channels on link protocol

  • Support for double-length data packets for Intel Itanium Processor Family mode

  • Performance counters to enable software tuning

Each port on the crossbar ASIC has 8 GB/s of peak bandwidth. These ports provide a high- throughput path to cells and other crossbar ASICs:

  • Four ports connect to the four cells that reside on the crossbar ASIC (one port per cell).

  • Three ports connect to the remaining three crossbar ASICs (in an Integrity Superdome 64-way


The total crossbar bandwidth for each Integrity Superdome model is calculated as follows:

(Number of cells × peak crossbar bandwidth per cell) ÷ 2 ports Crossbar bandwidth for the different Integrity Superdome servers is excellent:

  • For the HP Integrity Superdome 16-processor or 16–mx2 Dual-Processor Module (32-CPU) server, the crossbar bandwidth is 16 GB/s.

  • For the HP Integrity Superdome 32-processor or 32–mx2 Dual-Processor Module (64-CPU) server, the crossbar bandwidth is 32 GB/s.

  • For the HP Integrity Superdome 64-processor or 64–mx2 Dual-Processor Module (128-CPU) server, the crossbar bandwidth is 64 GB/s.


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