On Tue, 12 Dec 2000, Graham Stoney wrote: > Also, doesn't the 8260 have seperate memory subsystems to help get > around this? > I assume you are referring to the local bus? Well yes, but there are large tradeoffs.
If you use the local bus for the receive buffers then you can have simultaneous CPM to local bus and CPU to 60x bus transactions. The catch is that the local bus can not be cached. So, you trade off bus contention for caching/bursting. The CPU must go across the 60x to local bus bridge for those transactions. The DMA engine can burst between the 60x and local busses. If the data has to end up in user space, it ends up being about a wash, given the checksum and user space copy. I need more testing to confirm this, though. If the user space copy was not needed, like for routing, then it might help some. -- Brian Ford Software Engineer Vital Visual Simulation Systems FlightSafety International Phone: 314-551-8460 Fax: 314-551-8444 ** Sent via the linuxppc-embedded mail list. See http://lists.linuxppc.org/
