OPB versus PLB

Could somebody explain me why the OPB bus is used for "slow" peripheral and the PLB bus for "fast" peripherals? I have a small design with both an OPB and PLB bus and both are running at 100 MHz. Of course there is a delay when access devices at the OPB bus from a PowerPC (OPB2PLB bridge). But is this the only delay or are there more (like burst supports etc.).

TIA, Frank

Reply to
Frank van Eijkelenburg
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Frank van Eijkelenburg wrote on 28.10.2004 09:55:

The PLB just has some features that make it better suited for high-speed accesses. You can do 64bit-transfers, simultaneous read and write, it's hooked up directly to the PPC (so there's no need for a bridge in between, which could add more delay), has less latency and so on. The PLB is specifically designed to connect your PPC to memories and other stuff that needs really high data rates.

The OPB on the other hand is designed to be as simple as possible (i.e. use little logic ressources) and interface as easily to your logic as possible. It just lacks some of the "advanced features" the PLB has. Doesn't necessarily mean it's a lot slower, just that the theoretical maximum throughput is a lot higher for the PLB.

cu, Sean

Reply to
Sean Durkin

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