Motorola MVME1X7P manual Programming Issues

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Programming Issues

The Petra ASIC is functionally compatible with each of the components that it replaces. In cases where functionality between ASICs is exclusive, configuration switches or jumpers are provided to let you select the desired functionality.

In several areas of functionality, the configuration switches provide backward compatibility with earlier MVME167/177 implementations, but you can override their settings in software if you wish. A “R/W” by the corresponding register table entry in this manual denotes instances where this override capability is present.

Where the older technology supported “fast page” or “EDO” DRAM chips, the Petra memory controllers support SDRAM devices. The two memory controllers modeled in Petra duplicate the functionality of the “parity” memory controller found in the MC ASICs used on certain other boards as well as that of the “single-bit error correcting/double-bit error detecting” memory controller found in the MCECC ASICs used on the MVME167/177.

This Programmer’s Reference Guide describes the MCECC model (in Chapter 4). In the MVME167/177 application, there is logic on the Petra chip to prevent you from inadvertently enabling the MC memory controller model.

The same SDRAM memory array serves both controller models. The SDRAM array is 32 data bits wide with 7 checkbits. The array architecture is a non-interleaved single bank for sizes below 32MB. For array sizes above 32MB, additional physical memory banks are added but the architecture remains non-interleaved.

A final note on the SDRAM implementation: The bandwidth between the SDRAM and local bus is greater than it was with the earlier DRAM array. As a result, software takes less time to execute. Applications that incorporate elapsed-time functions which are dependent on code execution may have problems.

For readers who need to know the ASIC-specific differences between the previous MCECC and Petra/MCECC programming models in detail, certain areas of the text in this manual are printed in italics and marked with change bars (as is done here). Readers should compare those sections to the corresponding sections of the first- and second-generation manuals.

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