Refactor TLBusWrapper and CrossingHelper #1548
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Move subsystem.SubsystemClockCrossing => diplomacy.ClockCrossingType Put abstract CrossingHelper base class in diplomacy Make concrete AXI4CrossingHelper, TLCrossingHelper, IntCrossingHelper Replace CrossingWrapper with AXI4CrossingWrapper, TLCrossingWrapper
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| class AXI4CrossingWrapper(val crossing: ClockCrossingType)(implicit p: Parameters) extends SimpleLazyModule with LazyScope { |
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If you split the crossing helpers by type like you've done, then I think this API (the wrapper) has to die. You typically need to cross more than one bus type and this wrapper can only cross AXI. So it's mostly useless.
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The way these wrappers work is to drop a half of the crossing in the island and place the other half in the caller. We need to IMO reconsider a few things: is the island a new module layer just doing the crossing? How do we relate multiple clocks each with multiple busses.
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On the one hand, you really want only one helper per clock domain in the island. On the other hand, you want to change the crossing type based on the relationship between that domain and the clock where the other half is dropped.
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We decided to:
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@terpstra I implemented the changes we discussed. Seems strictly better than before! I need to re-check the names before merging, but in the meantime can you unblock this PR? |
I refactored both the TLBusWrapper and CrossingHelper APIs. The former is slightly more flexible and has better code reuse. The latter is a complete re-write No intended functional RTL changes other than signal names.
TLBusWrapper:
CanAttachTLSlavesandCanAttachTLMastersCrossingHelper:
HasCrossingis deprecated,CrossingWrapperuses the replacement traitCrossesToOnlyOneClockDomainsubsystem.SubsystemClockCrossingtodiplomacy.ClockCrossingTypeHasClockDomainCrossingbase trait in diplomacy[Protocol][Out|In]wardCrossingHelpercase classes for each protocol type and[Protocol]ClockDomainCrossingimplicit class conversions in each package to add crossing methods to instances ofHasClockDomainCrossingthat need to be crossedClockCrossingTypeargument to individual calls toCrossingHelpermethods