Chisel3: Bitwise negation operator - chisel

Question

There appears to be either a bug with or undocumented changes to the bitwise negation operator between chisel2 and chisel3.
Chisel3 code not working
import chisel3._
class bitwise_neg extends Module {
val io = new Bundle {
val in = Input(UInt(4.W))
val out = Output(UInt(4.W))
}
io.out := ~io.in
}
Error message generated for line containing "~":
type mismatch; found : ()chisel3.core.Bits required: chisel3.core.Data
Chisel2 working code
import Chisel._
class bitwise_neg extends Module {
val io = new Bundle {
val in = UInt(INPUT, 4)
val out = UInt(OUTPUT, 4)
}
io.out := ~io.in
}
Any ideas on the new Chisel3 syntax or if this is a bug?

Answer 1

The problem is not related to the ~, you will get the same error even if you remove the ~. Just as jkoenig said, chisel3 requires that you wrap the io bundle in an IO() like this:
class bitwise_neg extends Module {
val io = IO(new Bundle {
val in = Input(UInt(4.W))
val out = Output(UInt(4.W))
})
io.out := ~io.in
}
If you want (but I wouldn't recommend it) you can use chisel2 notation using the compatibility layer in chisel3 with capital chisel import import Chisel._
import Chisel._
class bitwise_neg extends Module {
val io = new Bundle {
val in = UInt(INPUT, 4.W)
val out = UInt(OUTPUT, 4.W)
}
io.out := io.in
}