Re: Big Endian vs Little Endian

[Ira W. <iw...@ac...>]

James Harris wrote:

> 
> However the schematic clearly showed PPC D31 <-> PCI D0, PPC 30 <-> PCI D1.
> 
> This clearly reorders the entire 32 bits. As from my understanding PPC uses bit 31
> to indicate a value of 2^31 = .... and bit 0 to indicate 2^0 = 1. (This is where my
> thinking may be flawed.)
> 
> Now if the hardware IEEE1394 part has a method for reordering the data coming from
> the PCI bus then I understand why... It is because the PCI bus may be carrying
> reverse ordered bits NOT simply big endian.
> 

While I don't doubt what you are reading I know things don't work this
way.  There is something about IBM's naming convention which reorders
bits as well as bytes.  But that is only for documentation.  It has
nothing to do with the actual hardware...

What I do know for sure is that the PCI bus is "little-endian" and that
just byte-swapping works for 99.9999% of the things (cards etc.) out
there...  (Ok I made up that number but it is bassically true.  ;-)

What is always confusing (and we are trying to determine now) is who (or
what), when, and where data gets swapped.

Ira Weiny
iw...@ac...