Motorola MVME2300 Series manual Endian Conversion, Generating PCI Interrupt Acknowledge Cycles

Functional Description

Generating PCI Interrupt Acknowledge Cycles

Performing a read from the PIACK register will initiate a single PCI Interrupt Acknowledge cycle. Any single byte or combination of bytes may be read from, and the actual byte enable pattern used during the read will be passed on to the PCI bus. Upon completion of the PCI interrupt acknowledge cycle, the Raven will present the resulting vector information obtained from the PCI bus as read data.

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Endian Conversion

The Raven ASIC supports both big- and little-endian data formats. Since the PCI bus is inherently little-endian, conversion is necessary if all MPC devices are configured for big-endian operation. The Raven may be programmed to perform the endian conversion described below.

When MPC Devices are Big-Endian

When all MPC 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 MPC bus’s perspective. This association is true regardless of whether the transaction originates on the PCI bus or the MPC bus. Figure 2-7illustrates the concept.

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