Endian Conversion; When Ppc Devices Are Big-Endian - Motorola MVME2400 Series Programmer's Reference Manual

Hawk PCI Host Bridge & Multi-Processor Interrupt Controller
A special function is added to the PCI arbiter to hold the grant asserted
2
through a lock cycle. When the "POL" bit in the PCI arbiter control
register is set, the grant associated with the agent initiating the lock cycle
will be held asserted until the lock cycle is complete. If this bit is clear, the
arbiter does not distinguish between lock and non-lock cycle.

Endian Conversion

The PHB supports both Big- and Little-Endian data formats. Since the PCI
bus is inherently Little-Endian, conversion is necessary if all PPC devices
are configured for Big-Endian operation. The PHB may be programmed to
perform the Endian conversion described below.

When PPC Devices are Big-Endian

When all PPC devices are operating in Big-Endian mode, all data to/from
the PCI bus must be swapped such that the PCI bus looks big endian from
the PPC bus's perspective. This association is true regardless of whether
the transaction originates on the PCI bus or the PPC bus. This is shown in
Figure
2-38
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2-7.
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