{I,D}BusSimplePlugin: don't rely on memoryTranslatorPortConfig != null
#307
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`null` can be a valid `MemoryTranslator` configuration parameter, for example in the case of the `PmpPlugin`. Furthermore, the `IBusCachedPlugin` and `DBusCachedPlugin` do not generally rely on its `memoryTranslatorPortConfig` to be non-null to instantiate its translator port, but instead checks whether a `MemoryTranslator` service exists in the pipeline. Thus it seems best to change `IBusSimplePlugin` and `DBusSimplePlugin` to behave identically to the their respective cached versions. This also prevents accidental CPU misconfigurations where an MMU or PMP plugin is instantiated and generally usable, but does not actually take effect in the memory buses.
This is to avoid a combinational loop.
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Hi, sorry i missed that PR. |
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nullcan be a validMemoryTranslatorconfiguration parameter, for example in the case of thePmpPlugin. Furthermore, theIBusCachedPluginandDBusCachedPlugindo not generally rely on itsmemoryTranslatorPortConfigto be non-null to instantiate its translator port, but instead checks whether aMemoryTranslatorservice exists in the pipeline. Thus it seems best to changeIBusSimplePluginandDBusSimplePluginto behave identically to the their respective cached versions. This also prevents accidental CPU misconfigurations where an MMU or PMP plugin is instantiated and generally usable, but does not actually take effect in the memory buses.As an unintended side-effect, when pairing this change with use of the
PmpPluginorPmpPluginOld, this will now result in a combinational loop over theskipCmd,arbitration.isValid, andMMU_FAULTsignals. For now, I have simply avoided this by not settingskipCmdwhen there is anMMU_FAULT, given that this fault should still be caught despite a load being performed. While this seems to work for my initial tests,Hence this is a draft PR and I am looking for feedback on how to resolve the combinational loop issues.