Running rocket-chip through the chisel3 gsdt branch which supports stricter connection checks and uses implicit definitions to deal with "old" direction overrides, exposed a possible bug in the Scala compiler.
[error] .../src/main/scala/uncore/devices/Prci.scala:27: value asOutput is not a member of uncore.devices.PRCIInterrupts{val mtip: chisel3.core.Bool; val msip: chisel3.core.Bool}
[error] possible cause: maybe a semicolon is missing before `value asOutput'?
[error] }.asOutput
[error] ^
[error] one error found
[error] (uncore/compile:compileIncremental) Compilation failed
This change isn't strictly required for current chisel3 code, but is being submitted in anticipation of an eventual merge of the gsdt branch prior to a compiler fix.