Pass strings in Chisel

Question

Is there a method to pass strings in Chisel? For example, I want to pass a string ATGC and get the output as 0 for A, 1 for T, 2 for G and 3 for C . Is this possible? If yes, can anyone please elucidate? Thank you.

Using the code in the answer gives these errors:

[error] java.lang.NoSuchMethodException:  problems.ATGCHandler.main([Ljava.lang.String;)
[error]     at java.lang.Class.getMethod(Class.java:1786)
[error]     at sbt.Run.getMainMethod(Run.scala:99)
[error]     at sbt.Run.run0(Run.scala:86)
[error]     at sbt.Run.execute$1(Run.scala:65)
[error]     at sbt.Run.$anonfun$run$3(Run.scala:69)
[error]     at scala.runtime.java8.JFunction0$mcV$sp.apply(JFunction0$mcV$sp.java:12)
[error]     at scala.util.Try$.apply(Try.scala:209)
[error]     at sbt.Run.directExecute$1(Run.scala:69)
[error]     at sbt.Run.run(Run.scala:78)
[error]     at sbt.Defaults$.$anonfun$bgRunMainTask$6(Defaults.scala:1147)
[error]     at sbt.Defaults$.$anonfun$bgRunMainTask$6$adapted(Defaults.scala:1142)
[error]     at sbt.internal.BackgroundThreadPool.$anonfun$run$1(DefaultBackgroundJobService.scala:366)
[error]     at scala.runtime.java8.JFunction0$mcV$sp.apply(JFunction0$mcV$sp.java:12)
[error]     at scala.util.Try$.apply(Try.scala:209)
[error]     at sbt.internal.BackgroundThreadPool$BackgroundRunnable.run(DefaultBackgroundJobService.scala:289)
[error]     at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
[error]     at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
[error]     at java.lang.Thread.run(Thread.java:748)
[error] (Test / runMain) java.lang.NoSuchMethodException: problems.ATGCHandler.main([Ljava.lang.String;)

Answer 1

Chisel has some limited support for Characters which can be used to do String-like work. With careful handling of the encoding, you can write stuff like:

import chisel3._
import chisel3.util._
class ATGCHandler extends Module {
  val io = IO(new Bundle {
    val char = Input(UInt(8.W))
    val encoding = Output(Valid(UInt(2.W)))
  })
  // Defaults
  io.encoding.valid := false.B
  io.encoding.bits := DontCare
  // Encode Valid Inputs
  switch (io.char) {
    is ('A'.U) {
      io.encoding.valid := true.B
      io.encoding.bits := 0.U
    }
    is ('T'.U) {
      io.encoding.valid := true.B
      io.encoding.bits := 1.U
    }
    is ('G'.U) {
      io.encoding.valid := true.B
      io.encoding.bits := 2.U
    }
    is ('C'.U) {
      io.encoding.valid := true.B
      io.encoding.bits := 3.U
    }
  }
}

Or if you're feeling particularly Chisel-y, you could write the encoding as something like:

  // Encode Valid Inputs
  val mapping = Map('A' -> 0, 'T' -> 1, 'G' -> 2, 'C' -> 3)
  mapping.foreach { case (key, value) =>
    when (io.char === key.U) {
      io.encoding.valid := true.B
      io.encoding.bits := value.U
    }
  }

EDIT: To build this, you can use the following main function:

object ATGCDecoderMain {
  def main(args: Array[String]): Unit = {
    chisel3.Driver.execute(args, () => new ATGCDecoder)
  }
}