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tzechienchu/UART.scala

Created July 17, 2021 12:18
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UART from Chisel Book
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UART.scala
import chisel3._
import chisel3.util._
class Channel extends Bundle {
val data = Input(Bits(8.W))
val ready = Output(Bool())
val valid = Input(Bool())
}
//Single Bye Buffer
class Buffer extends Module {
val io = IO(new Bundle {
val in = new Channel()
val out = Flipped(new Channel())
})
val empty :: full :: Nil = Enum(2)
val stateReg = RegInit(empty)
val dataReg = RegInit(0.U(8.W))
io.in.ready := stateReg === empty
io.out.valid := stateReg === full
when (stateReg === empty) {
when (io.in.valid) {
dataReg := io.in.data
stateReg := full
}
} .otherwise {
when (io.out.ready) {
stateReg := empty
}
}
io.out.data := dataReg
}
class Tx(sysclk: Int, baudRate: Int) extends Module {
val io = IO(new Bundle {
val txd = Output(Bits(1.W))
val channel = new Channel()
})
val BIT_CNT = ((sysclk + baudRate/2)/baudRate -1).asUInt()
val shiftReg = RegInit(0x7ff.U)
val cntReg = RegInit(0.U(20.W))
val bitsReg = RegInit(0.U(4.W))
io.channel.ready := (cntReg === 0.U) && (bitsReg === 0.U)
io.txd := shiftReg(0)
when (cntReg === 0.U) {
cntReg := BIT_CNT
when (bitsReg =/= 0.U) {
val shift = shiftReg >> 1
shiftReg := Cat(1.U, shift(9,0))
bitsReg := bitsReg - 1.U
} .otherwise {
when (io.channel.valid) {
//2 Stop Bits , Data , Start
shiftReg := Cat(Cat(3.U, io.channel.data), 0.U)
bitsReg := 11.U
} .otherwise {
shiftReg := 0x7ff.U
}
}
} .otherwise {
cntReg := cntReg - 1.U
}
}
class BufferTx(sysclk: Int, baudRate: Int) extends Module {
val io = IO(new Bundle {
val txd = Output(Bits(1.W))
val channel = new Channel()
})
val tx = Module(new Tx(sysclk, baudRate))
val buf = Module(new Buffer())
buf.io.in <> io.channel
tx.io.channel <> buf.io.out
io.txd <> tx.io.txd
}
class Sender(sysclk: Int, baudRate: Int) extends Module {
val io = IO(new Bundle {
val txd = Output(Bits(1.W))
})
val tx = Module(new BufferTx(sysclk, baudRate))
io.txd := tx.io.txd
val msg = "Hello World"
val text = VecInit(msg.map(_.U))
val len = msg.length.U
val cntReg = RegInit(0.U(8.W))
tx.io.channel.data := text(cntReg)
tx.io.channel.valid := cntReg =/= len
when (tx.io.channel.ready && cntReg =/= len) {
cntReg := cntReg + 1.U
}
}
class Rx(sysclk: Int, baudRate: Int) extends Module {
val io = IO(new Bundle {
val rxd = Input(Bits(1.W))
val channel = Flipped(new Channel())
})
val BIT_CNT = ((sysclk + baudRate/2)/baudRate -1).asUInt()
val START_CNT = ((3*sysclk/2 + baudRate/2)/baudRate - 1).asUInt()
//Sync the Input rxd
val rxReg = RegNext(RegNext(io.rxd, 1.U), 1.U)
val shiftReg = RegInit('A'.U(8.W))
val cntReg = RegInit(0.U(20.W))
val bitsReg = RegInit(0.U(4.W))
val valReg = RegInit(false.B)
when (cntReg =/= 0.U) {
cntReg := cntReg - 1.U
} .elsewhen (bitsReg =/= 0.U) {
cntReg := BIT_CNT
shiftReg := Cat(rxReg, shiftReg >> 1)
bitsReg := bitsReg - 1.U
when (bitsReg === 1.U) {
valReg := true.B
}
//Start Wait
} .elsewhen( rxReg === 0.U) {
cntReg := START_CNT
bitsReg := 8.U
}
when (valReg && io.channel.ready) {
valReg := false.B
}
io.channel.data := shiftReg
io.channel.valid := valReg
}
class Echo(sysclk: Int, baudRate: Int) extends Module {
val io = IO(new Bundle {
val txd = Output(Bits(1.W))
val rxd = Input(Bits(1.W))
})
val tx = Module(new BufferTx(sysclk, baudRate))
val rx = Module(new Rx(sysclk, baudRate))
io.txd := tx.io.txd
rx.io.rxd := io.rxd
tx.io.channel <> rx.io.channel
}
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