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MPC8641D as RC, what are LAWs, ATMUs, and BARs ?

Question asked by David Eisenberg on Feb 5, 2008
Latest reply on Feb 27, 2012 by Pedro Rouhento

I am working with the MPC8641D (to be used as an RC device) and have some newbie confusion surrounding PCI Express usage and LAWs, ATMUs and BARs.


I read that LAWs map a region of 36 bit local address space to target interface.  Does this mean they assign MPC8641 internal addresses to its internal 'peripherals’ (PCIe, RapidIO, etc etc) ?   These are addresses on the so called “platform bus” ... absolutely nothing to do with the LBC or external address bus.


What then do ATMUs do ?  I did see they “translate a 36 bit local address to an external address, or translate an external address to a 36 bit local address space”.   What does “external address” refer to here ?  


If LAWs and ATMUs are overlapping in some way, why are they both needed ?


I am getting all of this confused with ‘traditional’ PCI BARs, and am not sure who is who anymore. 


I "see" things more clearly through graphical/pictorial representations .. any idea where I could find any ?


Thank you