BundleBridge: preserve width; don't use RegNext #2520
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RegNext erases the width of a UInt. This leads to: java.lang.IllegalArgumentException: requirement failed: hartPrefixNode.node (A nexus node with parent 'hartPrefixNode/topMod/topDesign/gen' at (BundleBridge.scala:144:31)) requires all outputs have equivalent Chisel Data types, but got UInt<10>(Wire in BundleBridgeNexus) vs UInt(Reg in BundleBridgeNexus) Using safeRegNext, we can keep the useful requirement check and still have BundleBridgeNexus work when registered=true with a UInt.
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Is there a chisel issue for "RegNext erases width of UInt"? |
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@mwachs5 IIRC, it has been discussed, and both the current and alternate behaviors are controversial, but since a change would break existing code that relies on this behavior, it remains as-is. cc @jackkoenig |
mwachs5
reviewed
Jun 12, 2020
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Upstream Chisel discussion about This is complicated and the current solution was to just document the behavior in chipsalliance/chisel#1318. |
hcook
approved these changes
Jun 12, 2020
hcook
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Jun 13, 2020
RegNext erases the width of a UInt. This leads to: java.lang.IllegalArgumentException: requirement failed: hartPrefixNode.node (A nexus node with parent 'hartPrefixNode/topMod/topDesign/gen' at (BundleBridge.scala:144:31)) requires all outputs have equivalent Chisel Data types, but got UInt<10>(Wire in BundleBridgeNexus) vs UInt(Reg in BundleBridgeNexus) Using safeRegNext, we can keep the useful requirement check and still have BundleBridgeNexus work when registered=true with a UInt.
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RegNext erases the width of a UInt.
This leads to:
java.lang.IllegalArgumentException: requirement failed: hartPrefixNode.node (A nexus node with parent 'hartPrefixNode/topMod/topDesign/gen' at (BundleBridge.scala:144:31)) requires all outputs have equivalent Chisel Data types, but got
UInt<10>(Wire in BundleBridgeNexus)
vs
UInt(Reg in BundleBridgeNexus)
Using safeRegNext, we can keep the useful requirement check and still have
BundleBridgeNexus work when registered=true with a UInt.
@jackkoenig FYI
Type of change: bug report
Impact: no functional change
Development Phase: implementation