Motorola MVME2300 Series - Manual (Page 258)

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Programming Details
5
big-endian mode, there should be no endian issues for Ethernet data. Big-
endian software, however, must still take the byte-swapping effect into
account when accessing the registers of the PCI-Ethernet device.
PCI-Graphics
Big-endian software must take the effects of byte swapping on big-endian
software into account.
Note On MVME2300 series boards this is not presently a
consideration, as no graphics are implemented on these
boards.
Role of the Universe ASIC
Since PCI is little-endian and the VMEbus is big-endian, the Universe
VMEbus interface chip 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 are expected to operate in big-endian mode, regardless of the
mode of operation in the processor’s domain.
In big-endian mode on the MVME2300 series boards, byte swapping is
performed by the Universe and then by the Raven. The result has the
desirable effect of being transparent to the big-endian software.
In little-endian mode, however, software must take the byte-swapping
effect of the Universe ASIC and the address reverse-rearranging effect of
the Raven into account.