diff --git a/lab1/src/main/scala/board/z710/z710/Top.scala b/lab1/src/main/scala/board/z710/z710/Top.scala
index fc7a85d..497168e 100644
--- a/lab1/src/main/scala/board/z710/z710/Top.scala
+++ b/lab1/src/main/scala/board/z710/z710/Top.scala
@@ -1,119 +1,103 @@
+// Copyright 2022 Canbin Huang
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
 package board.z710
 
-
 import chisel3._
-import chisel3.stage.ChiselStage
-import chisel3.util._
-import chisel3.{ChiselEnum, _}
-
-// import circt.stage.ChiselStage
-import chisel3.stage.ChiselGeneratorAnnotation
-
-import bus._
+import chisel3.stage.{ChiselGeneratorAnnotation, ChiselStage}
+import chisel3.util.Cat
 import peripheral._
-import riscv._
 import riscv.Parameters
-import riscv.core.CPU
-import javax.print.SimpleDoc
+import riscv.core.{CPU, ProgramCounter}
 
-object BootStates extends ChiselEnum {
-  val Init, Loading, BusWait, Finished = Value
-}
-
-
-class Top(binaryFilename: String ="say_goodbye.asmbin") extends Module {
-  // val binaryFilename = "say_goodbye.asmbin"
-  val io = IO(new Bundle {
-    // val switch = Input(UInt(16.W))
-
-    // val rgb = Output(UInt(12.W))
-
-    val led = Output(Bool())
+class Top(binaryFilename: String = "say_goodbye.asmbin") extends Module {
+  val io = IO(new Bundle() {
     val tx = Output(Bool())
     val rx = Input(Bool())
 
-
+    val led = Output(Bool())  // z710 has few LEDs, use one for running indicator
   })
-  val boot_state = RegInit(BootStates.Init)
+  val mem = Module(new Memory(Parameters.MemorySizeInWords))
+  // val hdmi_display = Module(new HDMIDisplay)
+  // val display = Module(new CharacterDisplay)
+  // val timer = Module(new Timer)
+  val uart = Module(new Uart(frequency = 32_000000, baudRate = 115200)) // 31M or 32M is good, 33M more error
+  val dummy = Module(new Dummy)
 
-  val uart = Module(new Uart(125_000_000, 115200))  // this freq is consistent with Zynq 7 PS UART module
+  // display.io.bundle <> dummy.io.bundle
+  mem.io.bundle <> dummy.io.bundle
+  mem.io.debug_read_address := 0.U
+  // timer.io.bundle <> dummy.io.bundle
+  uart.io.bundle <> dummy.io.bundle
   io.tx := uart.io.txd
   uart.io.rxd := io.rx
 
-  val cpu = Module(new CPU)
-  val mem = Module(new Memory(Parameters.MemorySizeInWords))
-  val timer = Module(new Timer)
-  val dummy = Module(new DummySlave)
-  val bus_arbiter = Module(new BusArbiter)
-  val bus_switch = Module(new BusSwitch)
-
   val instruction_rom = Module(new InstructionROM(binaryFilename))
   val rom_loader = Module(new ROMLoader(instruction_rom.capacity))
 
-  bus_arbiter.io.bus_request(0) := true.B
-
-  bus_switch.io.master <> cpu.io.axi4_channels
-  bus_switch.io.address := cpu.io.bus_address
-  for (i <- 0 until Parameters.SlaveDeviceCount) {
-    bus_switch.io.slaves(i) <> dummy.io.channels
-  }
-  rom_loader.io.load_address := Parameters.EntryAddress
-  rom_loader.io.load_start := false.B
   rom_loader.io.rom_data := instruction_rom.io.data
+  rom_loader.io.load_address := Parameters.EntryAddress
   instruction_rom.io.address := rom_loader.io.rom_address
-  cpu.io.stall_flag_bus := true.B
-  cpu.io.instruction_valid := false.B
-  bus_switch.io.slaves(0) <> mem.io.channels
-  rom_loader.io.channels <> dummy.io.channels
-  switch(boot_state) {
-    is(BootStates.Init) {
-      rom_loader.io.load_start := true.B
-      boot_state := BootStates.Loading
-      rom_loader.io.channels <> mem.io.channels
-    }
-    is(BootStates.Loading) {
-      rom_loader.io.load_start := false.B
-      rom_loader.io.channels <> mem.io.channels
-      when(rom_loader.io.load_finished) {
-        boot_state := BootStates.Finished
+
+  val CPU_clkdiv = RegInit(UInt(2.W),0.U)
+  val CPU_tick = Wire(Bool())
+  val CPU_next = Wire(UInt(2.W))
+  CPU_next := Mux(CPU_clkdiv === 3.U, 0.U, CPU_clkdiv + 1.U)
+  CPU_tick := CPU_clkdiv === 0.U
+  CPU_clkdiv := CPU_next
+
+  withClock(CPU_tick.asClock) {
+    val cpu = Module(new CPU)
+    // cpu.io.interrupt_flag := Cat(uart.io.signal_interrupt, timer.io.signal_interrupt)
+    // cpu.io.csr_regs_debug_read_address := 0.U
+    // cpu.io.regs_debug_read_address := 0.U
+    cpu.io.debug_read_address := 0.U
+    // cpu.io.memory_bundle.read_data := 0.U
+    cpu.io.instruction_valid := rom_loader.io.load_finished
+    mem.io.instruction_address := cpu.io.instruction_address
+    cpu.io.instruction := mem.io.instruction
+
+    when(!rom_loader.io.load_finished) {
+      rom_loader.io.bundle <> mem.io.bundle
+      cpu.io.memory_bundle.read_data := 0.U
+    }.otherwise {
+      rom_loader.io.bundle.read_data := 0.U
+      when(cpu.io.deviceSelect === 2.U) { // deviceSelect = highest 3 bits of address, thus 0x4000_0000 is mapped to UART
+        cpu.io.memory_bundle <> uart.io.bundle
+      }.otherwise {
+        cpu.io.memory_bundle <> mem.io.bundle
       }
     }
-    is(BootStates.Finished) {
-      cpu.io.stall_flag_bus := false.B
-      cpu.io.instruction_valid := true.B
-    }
   }
 
-  bus_switch.io.slaves(2) <> uart.io.channels
-  bus_switch.io.slaves(4) <> timer.io.channels
-
-  cpu.io.interrupt_flag := Cat(uart.io.signal_interrupt, timer.io.signal_interrupt)
-
-  cpu.io.debug_read_address := 0.U
-  mem.io.debug_read_address := 0.U
-
-
-  
-  val clock_freq = 100_000_000.U
-
+  // LED, blinks every second
+  val clock_freq = 40_000_000.U
   val led_count = RegInit(0.U(32.W))
-  when (led_count >= clock_freq) { // the led blinks every second, clock freq is 100M
+  when (led_count >= clock_freq) {
     led_count := 0.U
   }.otherwise {
     led_count := led_count + 1.U
   }
-
   io.led := (led_count >= (clock_freq >> 1))
 
 
+
 }
 
-
-
 object VerilogGenerator extends App {
-    (new ChiselStage).execute(
-        Array("-X", "verilog", "--target-dir", "verilog/z710"), 
-        Seq(ChiselGeneratorAnnotation(() => new Top())) // default bin file
-    )
-    
+  (new ChiselStage).execute(
+    Array("-X", "verilog", "-td", "verilog/z710"), 
+    Seq(ChiselGeneratorAnnotation(() => new Top("say_goodbye.asmbin")))   // program to run on CPU
+  )
 }
\ No newline at end of file
diff --git a/lab1/src/main/scala/peripheral/UART.scala b/lab1/src/main/scala/peripheral/UART.scala
new file mode 100644
index 0000000..2d47c57
--- /dev/null
+++ b/lab1/src/main/scala/peripheral/UART.scala
@@ -0,0 +1,204 @@
+// Copyright 2021 Howard Lau
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package peripheral
+
+import chisel3._
+import chisel3.util._
+
+class UartIO extends DecoupledIO(UInt(8.W)) {
+}
+
+
+/**
+ * Transmit part of the UART.
+ * A minimal version without any additional buffering.
+ * Use a ready/valid handshaking.
+ */
+class Tx(frequency: Int, baudRate: Int) extends Module {
+  val io = IO(new Bundle {
+    val txd = Output(UInt(1.W))
+    val channel = Flipped(new UartIO())
+
+  })
+
+  val BIT_CNT = ((frequency + baudRate / 2) / baudRate - 1).U
+
+  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) {
+        shiftReg := Cat(Cat(3.U, io.channel.bits), 0.U) // two stop bits, data, one start bit
+        bitsReg := 11.U
+      }.otherwise {
+        shiftReg := 0x7ff.U
+      }
+    }
+
+  }.otherwise {
+    cntReg := cntReg - 1.U
+  }
+}
+
+/**
+ * Receive part of the UART.
+ * A minimal version without any additional buffering.
+ * Use a ready/valid handshaking.
+ *
+ * The following code is inspired by Tommy's receive code at:
+ * https://github.com/tommythorn/yarvi
+ */
+class Rx(frequency: Int, baudRate: Int) extends Module {
+  val io = IO(new Bundle {
+    val rxd = Input(UInt(1.W))
+    val channel = new UartIO()
+
+  })
+
+  val BIT_CNT = ((frequency + baudRate / 2) / baudRate - 1).U
+  val START_CNT = ((3 * frequency / 2 + baudRate / 2) / baudRate - 1).U
+
+  // Sync in the asynchronous RX data, reset to 1 to not start reading after a reset
+  val rxReg = RegNext(RegNext(io.rxd, 1.U), 1.U)
+
+  val shiftReg = RegInit(0.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
+    // the last shifted in
+    when(bitsReg === 1.U) {
+      valReg := true.B
+    }
+  }.elsewhen(rxReg === 0.U) { // wait 1.5 bits after falling edge of start
+    cntReg := START_CNT
+    bitsReg := 8.U
+  }
+
+  when(valReg && io.channel.ready) {
+    valReg := false.B
+  }
+
+  io.channel.bits := shiftReg
+  io.channel.valid := valReg
+}
+
+/**
+ * A single byte buffer with a ready/valid interface
+ */
+class Buffer extends Module {
+  val io = IO(new Bundle {
+    val in = Flipped(new UartIO())
+    val out = new UartIO()
+  })
+
+  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.bits
+      stateReg := full
+    }
+  }.otherwise { // full
+    when(io.out.ready) {
+      stateReg := empty
+    }
+  }
+  io.out.bits := dataReg
+}
+
+/**
+ * A transmitter with a single buffer.
+ */
+class BufferedTx(frequency: Int, baudRate: Int) extends Module {
+  val io = IO(new Bundle {
+    val txd = Output(UInt(1.W))
+    val channel = Flipped(new UartIO())
+
+  })
+  val tx = Module(new Tx(frequency, baudRate))
+  val buf = Module(new Buffer)
+
+  buf.io.in <> io.channel
+  tx.io.channel <> buf.io.out
+  io.txd <> tx.io.txd
+}
+
+class Uart(frequency: Int, baudRate: Int) extends Module {
+  val io = IO(new Bundle {
+    val bundle = new RAMBundle
+    val rxd = Input(UInt(1.W))
+    val txd = Output(UInt(1.W))
+
+    val signal_interrupt = Output(Bool())
+  })
+  val interrupt = RegInit(false.B)
+  val rxData = RegInit(0.U)
+
+  val tx = Module(new BufferedTx(frequency, baudRate))
+  val rx = Module(new Rx(frequency, baudRate))
+
+  io.bundle.read_data := 0.U
+  when(io.bundle.address === 0x4.U) {
+    io.bundle.read_data := baudRate.U
+  }.elsewhen(io.bundle.address === 0xC.U) {
+    io.bundle.read_data := rxData
+    interrupt := false.B
+  }
+
+  tx.io.channel.valid := false.B
+  tx.io.channel.bits := 0.U
+  when(io.bundle.write_enable) {
+    when(io.bundle.address === 0x8.U) {
+      interrupt := io.bundle.write_data =/= 0.U
+    }.elsewhen(io.bundle.address === 0x10.U) {
+      tx.io.channel.valid := true.B
+      tx.io.channel.bits := io.bundle.write_data
+    }
+  }
+
+  io.txd := tx.io.txd
+  rx.io.rxd := io.rxd
+
+  io.signal_interrupt := interrupt
+  rx.io.channel.ready := false.B
+  when(rx.io.channel.valid) {
+    rx.io.channel.ready := true.B
+    rxData := rx.io.channel.bits
+    interrupt := true.B
+  }
+}