npc: reg file access through vpi

2024-03-29 10:35:49 +08:00 · 2024-03-29 10:35:49 +08:00 · 84c8de8461
commit 84c8de8461
parent dc2cb010ce
11 changed files with 378 additions and 145 deletions
--- a/npc/CMakeLists.txt
+++ b/npc/CMakeLists.txt
@ -1,91 +1,157 @@
-cmake_minimum_required(VERSION 3.20)
+cmake_minimum_required(VERSION 3.26)

 project(flow)
-set (CMAKE_CXX_STANDARD 11)
+set (CMAKE_CXX_STANDARD 14)
 cmake_policy(SET CMP0144 NEW)

+include(CMakeDependentOption)
+enable_testing()
+
+# -- Build options
+option(BUILD_USE_BLOOP "Whether to use bloop to spped up elaborate" ON)
+option(BUILD_SIM_TARGET "Whether to build verilator simulation binary" ON)
+cmake_dependent_option(BUILD_SIM_NVBOARD_TARGET "Whether to build nvboard target" OFF "BUILD_SIM_TARGET" OFF)
+option(ENABLE_YSYX_GIT_TRACKER "Ysyx tracker support" OFF)
+set(TOPMODULE "Flow" CACHE STRING "Topmodule name in chisel")
+
+# -- Ysyx tracker, configure
+if(ENABLE_YSYX_GIT_TRACKER)
  execute_process(
    COMMAND ${CMAKE_SOURCE_DIR}/../git_commit.sh "configure(npc)"
    WORKING_DIRECTORY ${CMAKE_SOURCE_DIR}/..
  )
+endif()

+# -- Check dependencies
+if(BUILD_SIM_TARGET)
+  find_package(verilator REQUIRED)
+endif()
+if(BUILD_SIM_NVBOARD_TARGET)
  find_package(SDL2 REQUIRED)
  find_package(SDL2_image REQUIRED)
-
-find_package(verilator REQUIRED)
+endif()

 find_library(NVBOARD_LIBRARY NAMES nvboard)
 find_path(NVBOARD_INCLUDE_DIR NAMES nvboard.h)

-set(TOPMODULES "Flow")
-
-foreach(TOPMODULE IN LISTS TOPMODULES)
- 
 # FIXME: all scala source file are tracked here, cause all files to rebuild 
 # after a source update. 
 set(SCALA_CORE "${CMAKE_CURRENT_SOURCE_DIR}/core")
 set(CHISEL_MODULE_CLASS "${CMAKE_PROJECT_NAME}.${TOPMODULE}")
+
+# Verilog files are generted in CHISEL_OUTPUT_TMP_DIR and copy to 
+# CHISEL_OUTPUT_DIR if content changes
+set(CHISEL_OUTPUT_DIR ${CMAKE_CURRENT_BINARY_DIR}/${TOPMODULE}/vsrc/)
+set(CHISEL_OUTPUT_TMP_DIR ${CMAKE_CURRENT_BINARY_DIR}/${TOPMODULE}/vsrc_tmp/)
+
+set(CHISEL_OUTPUT_VERILATOR_CONF ${CHISEL_OUTPUT_DIR}/conf.vlt)
+set(CHISEL_OUTPUT_TOPMODULE ${CHISEL_OUTPUT_DIR}/${TOPMODULE}.sv)
+set(CHISEL_EMIT_ARGS "--target-dir ${CHISEL_OUTPUT_TMP_DIR}")
+
+# -- Add an always run target to generate verilog files with sbt/bloop,
+#    as we don't know if the result files will be different from cmake
+# NOTE: Must reconfigure if we add new files in SCALA_CORE directory
 file(GLOB_RECURSE SCALA_CORE_SOURCES "${SCALA_CORE}/src/main/scala/*.scala")
-  file(GLOB_RECURSE SCALA_CORE_TEST_SOURCES "${SCALA_CORE}/src/test/scala/*.scala")
+file(GLOB_RECURSE SCALA_CORE_RESOURCES "${SCALA_CORE}/src/resource/*")
+set(CHISEL_DEPENDENCY ${SCALA_CORE_SOURCES} ${SCALA_CORE_RESOURCE} ${SCALA_CORE}/build.sbt)

-  # Configure time verilog source generation for verilator
+if(BUILD_USE_BLOOP)
+  set(CHISEL_TARGET bloop_${TOPMODULE})
+  set(CHISEL_TEST_TARGET bloop_${TOPMODULE}_test)
+  # Export sbt build config to bloop
+  if(NOT EXISTS ${SCALA_CORE}/.bloop)
    execute_process(
-    COMMAND sbt "runMain circt.stage.ChiselMain --target-dir ${CMAKE_CURRENT_BINARY_DIR}/${TOPMODULE}/vsrc --module ${CHISEL_MODULE_CLASS} --target verilog"
+      COMMAND sbt bloopInstall
      WORKING_DIRECTORY ${SCALA_CORE}
    )
-
+  endif()
+  string(REPLACE " " ";" CHISEL_EMIT_ARGS_LIST ${CHISEL_EMIT_ARGS})
+  list(TRANSFORM CHISEL_EMIT_ARGS_LIST PREPEND "--args;")
  add_custom_command(
-    OUTPUT ${CMAKE_CURRENT_BINARY_DIR}/${TOPMODULE}/vsrc/${TOPMODULE}.v
-    COMMAND sbt "runMain circt.stage.ChiselMain --target-dir ${CMAKE_CURRENT_BINARY_DIR}/${TOPMODULE}/vsrc --module ${CHISEL_MODULE_CLASS} --target verilog"
+    OUTPUT ${CHISEL_OUTPUT_TOPMODULE}
+    COMMAND bloop run root ${CHISEL_EMIT_ARGS_LIST}
+    COMMAND ${CMAKE_COMMAND} -E copy_directory_if_different ${CHISEL_OUTPUT_TMP_DIR} ${CHISEL_OUTPUT_DIR}
    WORKING_DIRECTORY ${SCALA_CORE}
-    DEPENDS ${SCALA_CORE_SOURCES}
+    DEPENDS ${CHISEL_DEPENDENCY}
+    COMMAND_EXPAND_LISTS
  )
+  add_test(
+    NAME bloop_${TOPMODULE}_test
+    COMMAND bloop test
+    WORKING_DIRECTORY ${SCALA_CORE}
+  )
+else()
+  set(CHISEL_TARGET sbt_${TOPMODULE})
+  set(CHISEL_TEST_TARGET sbt_${TOPMODULE}_test)
+  add_custom_command(
+    OUTPUT ${CHISEL_OUTPUT_TOPMODULE}
+    COMMAND sbt "run ${CHISEL_EMIT_ARGS}"
+    COMMAND ${CMAKE_COMMAND} -E copy_directory_if_different ${CHISEL_OUTPUT_TMP_DIR} ${CHISEL_OUTPUT_DIR}
+    WORKING_DIRECTORY ${SCALA_CORE}
+    DEPENDS ${CHISEL_DEPENDENCY}
+    VERBATIM
+  )
+  add_test(
+    NAME sbt_${TOPMODULE}_test
+    COMMAND sbt test
+    WORKING_DIRECTORY ${SCALA_CORE}
+  )
+endif()

-  add_custom_target(
-      ChiselBuild_${TOPMODULE}
-      DEPENDS ${CMAKE_CURRENT_BINARY_DIR}/${TOPMODULE}/vsrc/${TOPMODULE}.v
+if(NOT EXISTS ${CHISEL_OUTPUT_TOPMODULE})
+  # Probably cold build, generate verilog at configure time to produce top module file
+  execute_process(
+    COMMAND sbt "run ${CHISEL_EMIT_ARGS}"
+    WORKING_DIRECTORY ${SCALA_CORE}
  )
+  execute_process(
+    COMMAND ${CMAKE_COMMAND} -E copy_directory_if_different ${CHISEL_OUTPUT_TMP_DIR} ${CHISEL_OUTPUT_DIR}
+  )
+endif()

 # -- Build NVBoard executable
-
+if(BUILD_SIM_NVBOARD_TARGET)
  add_custom_command(
    OUTPUT ${CMAKE_CURRENT_BINARY_DIR}/${TOPMODULE}/auto_bind.cpp
    COMMAND auto_pin_bind ${CMAKE_SOURCE_DIR}/constr/${TOPMODULE}.nxdc ${CMAKE_CURRENT_BINARY_DIR}/${TOPMODULE}/auto_bind.cpp
    DEPENDS ${CMAKE_SOURCE_DIR}/constr/${TOPMODULE}.nxdc 
  )

-  unset(SOURCES)
  file(GLOB_RECURSE SOURCES csrc_nvboard/${TOPMODULE}/*.cpp)
  add_executable(V${TOPMODULE}_nvboard ${SOURCES} ${CMAKE_CURRENT_BINARY_DIR}/${TOPMODULE}/auto_bind.cpp)

  verilate(V${TOPMODULE}_nvboard TRACE THREADS
    TOP_MODULE ${TOPMODULE}
    PREFIX V${TOPMODULE}
-    SOURCES ${CMAKE_CURRENT_BINARY_DIR}/${TOPMODULE}/vsrc/${TOPMODULE}.v)
+    SOURCES ${CHISEL_OUTPUT_TOPMODULE}
+    INCLUDE_DIRS ${CMAKE_CURRENT_BINARY_DIR}/${TOPMODULE}/vsrc)

  add_dependencies(V${TOPMODULE}_nvboard ChiselBuild_${TOPMODULE})
  target_include_directories(V${TOPMODULE}_nvboard PRIVATE ${NVBOARD_INCLUDE_DIR} ${SDL2_INCLUDE_DIRS})
  target_link_libraries(V${TOPMODULE}_nvboard PRIVATE ${NVBOARD_LIBRARY} SDL2::SDL2 SDL2_image::SDL2_image)

  install(TARGETS V${TOPMODULE}_nvboard)
+endif()

 # -- Build Verilator executable and add to test
-
-  unset(SOURCES)
 file(GLOB_RECURSE SOURCES csrc/${TOPMODULE}/*.cpp)
 add_executable(V${TOPMODULE} ${SOURCES})

 verilate(V${TOPMODULE} TRACE COVERAGE THREADS
  TOP_MODULE ${TOPMODULE}
  PREFIX V${TOPMODULE}
-    SOURCES ${CMAKE_CURRENT_BINARY_DIR}/${TOPMODULE}/vsrc/${TOPMODULE}.v)
+  SOURCES ${CHISEL_OUTPUT_TOPMODULE} ${CHISEL_OUTPUT_VERILATOR_CONF}
+  INCLUDE_DIRS ${CMAKE_CURRENT_BINARY_DIR}/${TOPMODULE}/vsrc
+  VERILATOR_ARGS
+    "--vpi"   # Enable VPI
+    
+)

-  add_dependencies(V${TOPMODULE} ChiselBuild_${TOPMODULE})

-  enable_testing()
 add_test(NAME V${TOPMODULE} COMMAND V${TOPMODULE})

 # -- Add build tracking
+if(ENABLE_YSYX_GIT_TRACKER)
  add_custom_command(
      TARGET V${TOPMODULE}_nvboard PRE_BUILD
      COMMAND ${CMAKE_SOURCE_DIR}/../git_commit.sh "build_${CMAKE_PROJECT_NAME}_V${TOPMODULE}_nvboard"
@ -97,5 +163,4 @@ foreach(TOPMODULE IN LISTS TOPMODULES)
      COMMAND ${CMAKE_SOURCE_DIR}/../git_commit.sh "build_${CMAKE_PROJECT_NAME}_V${TOPMODULE}"
      WORKING_DIRECTORY ${CMAKE_SOURCE_DIR}/..
  )
-
-endforeach()
+endif()
--- a/npc/core/build.sbt
+++ b/npc/core/build.sbt
@ -3,6 +3,7 @@ ThisBuild / version          := "0.1.0"


 val chiselVersion = "6.2.0"
+val circeVersion  = "0.14.1"

 lazy val root = (project in file("."))
  .settings(
@ -10,8 +11,13 @@ lazy val root = (project in file("."))
    libraryDependencies ++= Seq(
      "org.chipsalliance" %% "chisel" % chiselVersion,
      "edu.berkeley.cs" %% "chiseltest" % "6.0.0" % "test",
-      "com.chuusai" %% "shapeless" % "2.3.3"
-    ),
+      "com.chuusai" %% "shapeless" % "2.3.3",
+      "com.github.scopt" %% "scopt" % "4.1.0",
+    ) ++ Seq(
+      "io.circe" %% "circe-core",
+      "io.circe" %% "circe-generic",
+      "io.circe" %% "circe-parser"
+    ).map(_ % circeVersion),
    scalacOptions ++= Seq(
      "-language:reflectiveCalls",
      "-deprecation",
--- a/npc/core/src/main/scala/FlowMain.scala
+++ b/npc/core/src/main/scala/FlowMain.scala
@ -5,16 +5,17 @@ import chisel3._
 import chisel3.util.{MuxLookup, Fill, Decoupled, Counter, Queue, Reverse}
 import chisel3.util.{SRAM}
 import chisel3.util.experimental.decode.{decoder, TruthTable}
-import chisel3.stage.ChiselOption
 import chisel3.util.log2Ceil
 import chisel3.util.BitPat
 import chisel3.util.Enum
-import chisel3.experimental.prefix
+import chisel3.experimental.Trace._
 import shapeless.{HNil, ::}
 import shapeless.HList
 import shapeless.ops.coproduct.Prepend
 import chisel3.util.{ BinaryMemoryFile, HexMemoryFile }

+import chisel3.experimental.Trace
+
 object RV32Inst {
  private val bp = BitPat
  val addi = this.bp("b???????_?????_?????_000_?????_00100_11")
@ -73,7 +74,7 @@ class Control(width: Int) extends Module {
    })
 }

-import flow.components.{RegisterFile, RegFileInterface, ProgramCounter, ALU}
+import flow.components.{RegisterFile, ProgramCounter, ALU}
 import chisel3.util.experimental.loadMemoryFromFileInline
 class Flow extends Module {
  val dataType = UInt(32.W)
@ -87,7 +88,7 @@ class Flow extends Module {
    memoryFile = HexMemoryFile("./resource/addi.txt")
  )
  val control = Module(new Control(32))
-  val reg = RegisterFile(32, dataType, 2, 2)
+  val reg = Module(new RegisterFile(dataType, 32, 2))
  val pc = Module(new ProgramCounter(dataType))
  val alu = Module(new ALU(dataType))

@ -95,6 +96,9 @@ class Flow extends Module {
  ram.readPorts(0).address := pc.out - 0x80000000L.U
  val inst = ram.readPorts(0).data

+  Trace.traceName(reg.control.writeEnable)
+  dontTouch(reg.control.writeEnable)
+
  import control.pc.SrcSelect._

  pc.in.pcSrcs(pStaticNpc.litValue.toInt) := pc.out + 4.U
@ -125,5 +129,6 @@ class Flow extends Module {
  alu.in.a(aSrcImm.litValue.toInt) := inst(31, 20)
  alu.in.b := reg.out.src(1)

+
  dontTouch(control.out)
 }
--- a/npc/core/src/main/scala/Mem.scala
+++ b/npc/core/src/main/scala/Mem.scala
@ -0,0 +1 @@
+package flow.components
--- a/npc/core/src/main/scala/RegisterFile.scala
+++ b/npc/core/src/main/scala/RegisterFile.scala
@ -4,6 +4,7 @@ import chisel3._
 import chisel3.util.log2Ceil
 import chisel3.util.UIntToOH
 import chisel3.util.MuxLookup
+import chisel3.experimental.Trace._
 import shapeless.{ HNil, :: }

 class RegControl extends Bundle {
@ -18,69 +19,34 @@ class RegControl extends Bundle {
  def ctrlBindPorts: CtrlTypes = {
    writeEnable :: writeSelect :: HNil
  }
+  traceName(writeEnable)
 }

-class RegFileData[T <: Data](size:Int, tpe: T, numReadPorts: Int, numWritePorts: Int) extends Bundle {
-  val write = new Bundle {
-    val addr = Input(UInt(size.W))
-    val data = Vec(numWritePorts, Input(tpe))
-  }
-  val read = Vec(numReadPorts, new Bundle {
-    val rs = Input(UInt(size.W))
-    val src = Output(tpe)
-  })
-}
-
-class RegFileInterface[T <: Data](size: Int, tpe: T, numReadPorts: Int, numWritePorts: Int) extends Bundle {
-  val control = new RegControl
-  // val data = new RegFileData(size, tpe, numReadPorts, numWritePorts)
-  val in = new Bundle {
-    val writeAddr = Input(UInt(size.W))
-    val writeData = Input(Vec(numWritePorts, tpe))
-    val rs = Input(Vec(numReadPorts, UInt(size.W)))
-  }
-  val out = new Bundle {
-    val src = Output(Vec(numReadPorts, tpe))
-  }
-}
-
-class RegisterFileCore[T <: Data](size: Int, tpe: T, numReadPorts: Int) extends Module {
+class RegisterFile[T <: Data](tpe: T, regCount: Int, numReadPorts: Int) extends Module {
  require(numReadPorts >= 0)
-  val writePort = IO(new Bundle {
-    val enable = Input(Bool())
-    val addr = Input(UInt(log2Ceil(size).W))
-    val data = Input(tpe)
+  val control = IO(new RegControl)
+  val dataAddrWidth = log2Ceil(tpe.getWidth).W
+  val in = IO(new Bundle {
+    val writeAddr = Input(UInt(dataAddrWidth))
+    val writeData = Input(Vec(control.WriteSelect.all.length, tpe))
+    val rs = Input(Vec(numReadPorts, UInt(dataAddrWidth)))
+  })
+  val out = IO(new Bundle {
+    val src = Output(Vec(numReadPorts, tpe))
  })
-  val readPorts = IO(Vec(numReadPorts, new Bundle {
-    val addr = Input(UInt(log2Ceil(size).W))
-    val data = Output(tpe)
-  }))

-  val regFile = RegInit(VecInit(Seq.fill(size)(0.U(tpe.getWidth.W))))
-  val writeAddrOH = UIntToOH(writePort.addr)
+  val regResetValue = 0.U(tpe.getWidth.W)
+  val regFile = RegInit(VecInit(Seq.fill(regCount)(regResetValue)))
+  val writeAddrOH = UIntToOH(in.writeAddr)
+
  for ((reg, i) <- regFile.zipWithIndex.tail) {
-    reg := Mux(writeAddrOH(i) && writePort.enable, writePort.data, reg)
+    reg := Mux(writeAddrOH(i.U(log2Ceil(regCount).W)) && control.writeEnable, in.writeData(control.writeSelect.asUInt), reg)
  }
  regFile(0) := 0.U

-  for (readPort <- readPorts) {
-    readPort.data := regFile(readPort.addr)
+  for (port <- 0 until numReadPorts) {
+    out.src(port) := regFile(in.rs(port).asUInt)
  }
+  traceName(regFile)
  dontTouch(regFile)
 }
-
-object RegisterFile {
-  def apply[T <: Data](size: Int, tpe: T, numReadPorts: Int, numWritePorts: Int): RegFileInterface[T] = {
-    val core = Module(new RegisterFileCore(size, tpe, numReadPorts))
-    val _out = Wire(new RegFileInterface(size, tpe, numReadPorts, numWritePorts))
-    val clock = core.clock
-    for (i <- 0 until numReadPorts) {
-      core.readPorts(i).addr := _out.in.rs(i)
-      _out.out.src(i) := core.readPorts(i).data
-    }
-    core.writePort.addr := _out.in.writeAddr
-    core.writePort.data := _out.in.writeData(_out.control.writeSelect.asUInt)
-    core.writePort.enable := _out.control.writeEnable
-    _out
-  }
-}
--- a/npc/core/src/main/scala/top/ArgParse.scala
+++ b/npc/core/src/main/scala/top/ArgParse.scala
@ -0,0 +1,47 @@
+package flow
+
+import scopt.{ OParser, DefaultOEffectSetup }
+import java.io.File
+
+case class CliOptions(
+    targetDir: File = new File("."),
+    configFile: Option[File] = None,
+    argsFile: Option[File] = None,
+    verilatorConfigFileOut: File = new File("conf.vlt"),
+) {
+  val builder = OParser.builder[CliOptions]
+  val parser =  {
+    import builder._
+    OParser.sequence(
+      programName("flow"),
+      help("help"),
+      opt[Option[File]]('c', "config")
+        .action((x, c) => c.copy(configFile = x))
+        .text("JSON Configuration file for generation"),
+      opt[Option[File]]("args-file")
+        .action((x, c) => c.copy(argsFile = x))
+        .text("Passing file content as args when emit"),
+      opt[File]('o', "target-dir")
+        .action((x, c) => c.copy(targetDir = x))
+        .text("Output files relative to this path"),
+      opt[File]("out-verilator-conf")
+        .action((x, c) => c.copy(verilatorConfigFileOut = x))
+        .text("Options needed when simulating with verilator")
+    )
+  }
+
+  def parse(args: Array[String]): CliOptions = {
+    OParser.runParser(parser, args, CliOptions()) match {
+      case (result, effects) =>
+        OParser.runEffects(effects, new DefaultOEffectSetup {
+          // ignore terminate
+          override def terminate(exitState: Either[String, Unit]): Unit = ()
+        })
+
+        result match {
+          case Some(cliOptions: CliOptions) => { return cliOptions }
+          case _ => { throw new IllegalArgumentException("Wrong command line argument") }
+        }
+    }
+  }
+}
--- a/npc/core/src/main/scala/top/Config.scala
+++ b/npc/core/src/main/scala/top/Config.scala
@ -0,0 +1,16 @@
+package flow
+
+import io.circe.generic.JsonCodec
+
+// Which group of signals to trace
+@JsonCodec case class TraceConfig (
+  enable: Boolean = false,
+  registers: Array[Int] = Array(),
+  mem: Array[(Int, Int)] = Array(),
+)
+
+@JsonCodec case class Config(
+  // Whether to enable Difftest
+  enableDifftest: Boolean = true,
+  traceConfig: TraceConfig = TraceConfig(),
+)
--- a/npc/core/src/main/scala/top/Main.scala
+++ b/npc/core/src/main/scala/top/Main.scala
@ -0,0 +1,72 @@
+package flow
+
+import flow._
+
+import chisel3._
+import chisel3.experimental.Trace._
+import chisel3.stage.{ChiselGeneratorAnnotation, DesignAnnotation}
+import chisel3.util.experimental.InlineInstance
+import circt.stage.ChiselStage
+import firrtl.AnnotationSeq
+import firrtl.annotations.TargetToken.{Instance, OfModule, Ref}
+import java.io.PrintWriter
+import scala.io.Source
+import java.io.File
+
+
+// TODO: Generate verilator config file
+
+object VerilogMain extends App {
+  val opt = CliOptions().parse(args)
+  val topName = "Flow"
+
+  val config: Config = opt.configFile match {
+    case Some(f) => {
+      val source = Source.fromFile(f)
+      val jsonString = source.mkString
+      source.close()
+      io.circe.parser.decode[Config](jsonString) match {
+        case Right(x) => x
+        case Left(e) => throw e
+      }
+    }
+    case None => Config(traceConfig = TraceConfig(enable = true))
+  }
+
+  val annos = (new ChiselStage).execute(
+    Array("--target-dir", opt.targetDir.toString, "--target", "systemverilog", "--split-verilog"),
+    Seq(
+
+    ) ++ (if(config.traceConfig.enable) Seq(ChiselGeneratorAnnotation(() => new Flow)) else Seq())
+  )
+
+  if(config.traceConfig.enable) {
+    val dut = annos.collectFirst { case DesignAnnotation(dut) => dut }.get.asInstanceOf[Flow]
+
+    val verilatorConfigSeq = finalTargetMap(annos)
+      .values
+      .flatten
+      .map(ct =>
+        s"""public_flat_rd -module "${
+          ct.tokens.collectFirst { case OfModule(m) => m }.get
+        }" -var "${ct.tokens.collectFirst { case Ref(r) => r }.get}"""")
+    finalTargetMap(annos)
+      .values
+      .flatten
+      .foreach(
+        ct => println(s"""TOP.${ct.circuit}.${ct.path.map { case (Instance(i), _) => i }.mkString(".")}.${ct.tokens.collectFirst {
+          case Ref(r) => r
+        }.get}""") 
+      )
+    
+    val verilatorConfigWriter = new PrintWriter(new File(opt.targetDir, opt.verilatorConfigFileOut.toString()))
+    verilatorConfigWriter.write("`verilator_config\n")
+    try {
+      for(ct <- verilatorConfigSeq) {
+        verilatorConfigWriter.println(ct)
+      }
+    } finally {
+      verilatorConfigWriter.close()
+    }
+  }
+}
--- a/npc/core/src/main/scala/utils/DPI.scala
+++ b/npc/core/src/main/scala/utils/DPI.scala
@ -0,0 +1,11 @@
+package flow.utils
+
+import chisel3._
+import chisel3.util.HasBlackBoxResource
+
+// class DiffTester extends BlackBox with HasBlackBoxResource {
+//     val io = IO(new Bundle {
+//         val regs = 
+//     })
+//     addResource("difftest.v");
+// }
--- a/npc/csrc/Flow/main.cpp
+++ b/npc/csrc/Flow/main.cpp
@ -1,36 +1,80 @@
+#include <vpi_user.h>
+#include <VFlow.h>
 #include <cstdlib>
-#include <cassert>
-#include <cstdlib>
+#include <vector>
+#include <memory>
 #include <verilated.h>
 #include <verilated_vcd_c.h>
-#include <VFlow.h>
+#include <verilated_vpi.h>
+#include <string>
 #define MAX_SIM_TIME 100
 #define VERILATOR_TRACE

+std::vector<vpiHandle> regsHandle;
+int regs[32];
+
+static void init_vpi_regs() {
+  std::string regfile = "TOP.Flow.reg_0.regFile_";
+  for(int i = 0; i < 32; i++) {
+    std::string regname = regfile + std::to_string(i);
+    vpiHandle vh = vpi_handle_by_name((PLI_BYTE8 *)regname.c_str(), NULL);
+    regsHandle.push_back(vh);
+  }
+}
+
+static void init_vpi() {
+  init_vpi_regs();
+}
+
+static int vpi_get_int(vpiHandle vh) {
+  s_vpi_value v;
+  v.format = vpiIntVal;
+  vpi_get_value(vh, &v);
+  return v.value.integer;
+}
+
+static void update_regs() {
+  for(int i = 0; i < 32; i++) {
+    regs[i] = vpi_get_int(regsHandle[i]);
+  }
+}
+
+static void print_regs() {
+  for(int i = 0; i < 32; i++) {
+    printf("%d: %d\t", i, regs[i]);
+    if(i % 8 == 7) putchar('\n');
+  }
+  putchar('\n');
+}
+
+static int sim_time = 0;
+
 int main(int argc, char **argv, char **env) {
  int sim_time = 0;
+  int posedge_cnt = 0;
  Verilated::commandArgs(argc, argv);

-    VFlow *top = new VFlow;
-
+  std::unique_ptr<VFlow> top{new VFlow};
  Verilated::traceEverOn(true);
  VerilatedVcdC *m_trace = new VerilatedVcdC;
 #ifdef VERILATOR_TRACE
  top->trace(m_trace, 5);
  m_trace->open("waveform.vcd");
 #endif
-    for (sim_time = 0; sim_time < 10; sim_time++) {
-        top->eval();
-        top->clock = !top->clock;
-        top->reset = 1;
-#ifdef VERILATOR_TRACE
-        m_trace->dump(sim_time);
-#endif
-    }
+
+  init_vpi();
+
  top->reset = 0;
  for (sim_time = 10; sim_time < MAX_SIM_TIME; sim_time++) {
    top->eval();
    top->clock = !top->clock;
+    if(top->clock == 1) {
+      // Posedge
+      ++posedge_cnt;
+      update_regs();
+      print_regs();
+    }
+
 #ifdef VERILATOR_TRACE
    m_trace->dump(sim_time);
 #endif
@ -38,6 +82,5 @@ int main(int argc, char **argv, char **env) {
 #ifdef VERILATOR_TRACE
  m_trace->close();
 #endif
-    delete top;
  exit(EXIT_SUCCESS);
 }
--- a/npc/flake.nix
+++ b/npc/flake.nix
@ -20,9 +20,10 @@
          CHISEL_FIRTOOL_PATH = "${nixpkgs-circt162.legacyPackages.${system}.circt}/bin";
          packages = [
            clang-tools
-            # rnix-lsp
+            cmake
            coursier
            espresso
+            bloop

            gdb
            jre