val reg = RegInit(0.U(8.W))  //ok
val reg = RegInit(0.UInt(8.W))  //err

U 使用在数字 . 后边50.U

UInt 使用在IO(new Bundle val a = Input(UInt(8.W)) 或者 def counter(max:UInt, a1:UInt)

package empty

import chisel3._
import chisel3.util._

class MyCounter extends Module {
  val io = IO(new Bundle {
    val a = Input(UInt(8.W))  
    //val a = Input(U(8.W)) 
    val c = Output(UInt(8.W))
  })
  val init = io.a

	def counter(max:UInt, a1:UInt) ={  //max:U  //err
		
		val reg = RegInit(a1)   //ok
		//val reg = RegInit(0.U(8.W))  //ok
		//val reg = RegInit(0.UInt(8.W))  //err
		
		when(reg===max) {
		  reg := 0.U(max.getWidth.W)
		}.otherwise {
		  reg := reg + 1.U(1.W)
		}
		reg  // return value
		
	}
  io.c := counter(50.U, io.a)
}

object MyCounterMain extends App {
  println("Generating the adder hardware")
  emitVerilog(new MyCounter(), Array("--target-dir", "generated"))
}