Motorola MVME2400 用户手册
Programming Considerations
http://www.mcg.mot.com/literature
4-11
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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, however.
software must still take the byte-swapping effect into account when
accessing the registers of the PCI/Ethernet device, however.
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.
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.
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).
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.
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.
Series VME Processor Module Programmer’s Reference Guide.