Vmebus Domain - Motorola MVME2400 Series Installation And Use Manual

PCI and Ethernet
Ethernet is byte-stream-oriented; the byte having the lowest address in
memory is the first one to be transferred regardless of the endian mode.
Since the PHB maintains address invariance in both little-endian and
big-endian mode, no endian issues should arise for Ethernet data.
Big-endian software must still take the byte-swapping effect into account
when accessing the registers of the PCI/Ethernet device.
Role of the Universe ASIC
Because the PCI bus is little-endian while the VMEbus is big-endian, the
Universe PCI/VME bus bridge ASIC performs byte swapping in both
directions (from PCI to VMEbus and from VMEbus to PCI) to maintain
address invariance, regardless of the mode of operation in the processor's
domain.

VMEbus Domain

The VMEbus is inherently big-endian. All devices connected directly to
the VMEbus must operate in big-endian mode, regardless of the mode of
operation in the processor's domain.
In big-endian mode, byte-swapping is performed first by the Universe
ASIC and then by the PHB. The result is transparent to big-endian
software (a desirable effect).
In little-endian mode, however, software must take the byte-swapping
effect of the Universe ASIC and the address reverse-rearranging effect of
the PHB into account.
For further details on endian considerations, refer to the MVME2400
Series VME Processor Module Programmer's Reference Guide.
http://www.motorola.com/computer/literature
Programming Considerations
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