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On-chip Busses Summary.

Multiplexing using tri-states is common at the PCB level but active multiplexors result in less energy use for on-chip use.

It is handy if all of the IP blocks to be integrated conform to a common bus bus port standard.

Automatic synthesis of glue logic and memory maps is possible (see HLS section of these notes, if lectured).

Formal specifications of bus ports are widely used, assisting in tool automation and ABD.

The AMBA AHB bus from ARM Cambridge was widely used: but is quite complex and was intolerant of additional pipeline stages being inserted between initiator and responder (i.e. had no temporal decoupling).

The OCP BVCI supports temporal decoupling, but requests and responses must not overtake: hence it can cross clock domains and tolerate pipeline stages. But it cannot tolerate reordered responses (e.g. from a DRAM).

One ARM AXI protocol includes tags on each operation for out-of-order request/response association: hence it is suitable for pipelined, on-chip networks where message sequencing may vary.

63: (C) 2008-13, DJ Greaves, University of Cambridge, Computer Laboratory.