// See LICENSE.jtag for license details.

package freechips.rocketchip.jtag

import chisel3._
import chisel3.util._
import freechips.rocketchip.config.{Parameters}
import freechips.rocketchip.util.property._

object JtagState {
  sealed abstract class State(val id: Int) {
    def U: UInt = id.U(State.width.W)
  }

  object State {
    import scala.language.implicitConversions

    implicit def toInt(x: State) = x.id
    implicit def toBigInt(x: State):BigInt = x.id

    // TODO: this could be automatically generated with macros and stuff
    val all: Set[State] = Set(
      TestLogicReset,
      RunTestIdle,
      SelectDRScan,
      CaptureDR,
      ShiftDR,
      Exit1DR,
      PauseDR,
      Exit2DR,
      UpdateDR,
      SelectIRScan,
      CaptureIR,
      ShiftIR,
      Exit1IR,
      PauseIR,
      Exit2IR,
      UpdateIR
    )
    val width = log2Ceil(all.size)
    def chiselType() = UInt(width.W)
  }

  // States as described in 6.1.1.2, numeric assignments from example in Table 6-3
  case object TestLogicReset extends State(15)  // no effect on system logic, entered when TMS high for 5 TCK rising edges
  case object RunTestIdle extends State(12)  // runs active instruction (which can be idle)
  case object SelectDRScan extends State(7)
  case object CaptureDR extends State(6)  // parallel-load DR shifter when exiting this state (if required)
  case object ShiftDR extends State(2)  // shifts DR shifter from TDI towards TDO, last shift occurs on rising edge transition out of this state
  case object Exit1DR extends State(1)
  case object PauseDR extends State(3)  // pause DR shifting
  case object Exit2DR extends State(0)
  case object UpdateDR extends State(5)  // parallel-load output from DR shifter on TCK falling edge while in this state (not a rule?)
  case object SelectIRScan extends State(4)
  case object CaptureIR extends State(14)  // parallel-load IR shifter with fixed logic values and design-specific when exiting this state (if required)
  case object ShiftIR extends State(10)  // shifts IR shifter from TDI towards TDO, last shift occurs on rising edge transition out of this state
  case object Exit1IR extends State(9)
  case object PauseIR extends State(11)  // pause IR shifting
  case object Exit2IR extends State(8)
  case object UpdateIR extends State(13)  // latch IR shifter into IR (changes to IR may only occur while in this state, latch on TCK falling edge)
}

/** The JTAG state machine, implements spec 6.1.1.1a (Figure 6.1)
  *
  * Usage notes:
  * - 6.1.1.1b state transitions occur on TCK rising edge
  * - 6.1.1.1c actions can occur on the following TCK falling or rising edge
  *
  */
class JtagStateMachine(implicit val p: Parameters) extends Module() {
  class StateMachineIO extends Bundle {
    val tms = Input(Bool())
    val currState = Output(JtagState.State.chiselType)
  }
  val io = IO(new StateMachineIO)

  val nextState = WireInit(JtagState.TestLogicReset.U)
  val currState = RegNext(next=nextState, init=JtagState.TestLogicReset.U)

  switch (currState) {
    is (JtagState.TestLogicReset.U) {
      nextState := Mux(io.tms, JtagState.TestLogicReset.U, JtagState.RunTestIdle.U)
    }
    is (JtagState.RunTestIdle.U) {
      nextState := Mux(io.tms, JtagState.SelectDRScan.U, JtagState.RunTestIdle.U)
    }
    is (JtagState.SelectDRScan.U) {
      nextState := Mux(io.tms, JtagState.SelectIRScan.U, JtagState.CaptureDR.U)
    }
    is (JtagState.CaptureDR.U) {
      nextState := Mux(io.tms, JtagState.Exit1DR.U, JtagState.ShiftDR.U)
    }
    is (JtagState.ShiftDR.U) {
      nextState := Mux(io.tms, JtagState.Exit1DR.U, JtagState.ShiftDR.U)
    }
    is (JtagState.Exit1DR.U) {
      nextState := Mux(io.tms, JtagState.UpdateDR.U, JtagState.PauseDR.U)
    }
    is (JtagState.PauseDR.U) {
      nextState := Mux(io.tms, JtagState.Exit2DR.U, JtagState.PauseDR.U)
    }
    is (JtagState.Exit2DR.U) {
      nextState := Mux(io.tms, JtagState.UpdateDR.U, JtagState.ShiftDR.U)
    }
    is (JtagState.UpdateDR.U) {
      nextState := Mux(io.tms, JtagState.SelectDRScan.U, JtagState.RunTestIdle.U)
    }
    is (JtagState.SelectIRScan.U) {
      nextState := Mux(io.tms, JtagState.TestLogicReset.U, JtagState.CaptureIR.U)
    }
    is (JtagState.CaptureIR.U) {
      nextState := Mux(io.tms, JtagState.Exit1IR.U, JtagState.ShiftIR.U)
    }
    is (JtagState.ShiftIR.U) {
      nextState := Mux(io.tms, JtagState.Exit1IR.U, JtagState.ShiftIR.U)
    }
    is (JtagState.Exit1IR.U) {
      nextState := Mux(io.tms, JtagState.UpdateIR.U, JtagState.PauseIR.U)
    }
    is (JtagState.PauseIR.U) {
      nextState := Mux(io.tms, JtagState.Exit2IR.U, JtagState.PauseIR.U)
    }
    is (JtagState.Exit2IR.U) {
      nextState := Mux(io.tms, JtagState.UpdateIR.U, JtagState.ShiftIR.U)
    }
    is (JtagState.UpdateIR.U) {
      nextState := Mux(io.tms, JtagState.SelectDRScan.U, JtagState.RunTestIdle.U)
    }
  }

  io.currState := currState

  // Generate Coverate Points
  JtagState.State.all.foreach { s => 
    cover (currState === s.U && io.tms === true.B,  s"${s.toString}_tms_1", s"JTAG; ${s.toString} with TMS = 1; State Transition from ${s.toString} with TMS = 1")
    cover (currState === s.U && io.tms === false.B, s"${s.toString}_tms_0", s"JTAG; ${s.toString} with TMS = 0; State Transition from ${s.toString} with TMS = 0")
   cover (currState === s.U && reset.asBool === true.B, s"${s.toString}_reset", s"JTAG; ${s.toString} with reset; JTAG Reset asserted during ${s.toString}")
 
  }

}
