diff --git a/flake.nix b/flake.nix
index b2e8142..c824872 100644
--- a/flake.nix
+++ b/flake.nix
@@ -111,12 +111,17 @@
             nixpkgs-circt162.legacyPackages.${system}.circt
             yosys
             cli11
+            flex
+            bison
+            verilator
           ];
 
           buildInputs = [
-            verilator
             nvboard
             openssl
+            libllvm
+            libxml2
+            readline
           ] ++ self.checks.${system}.pre-commit-check.enabledPackages;
 
           cmakeFlags = [
diff --git a/npc/CMakeLists.txt b/npc/CMakeLists.txt
index 78dbfe5..bcd356b 100644
--- a/npc/CMakeLists.txt
+++ b/npc/CMakeLists.txt
@@ -34,6 +34,10 @@ if(BUILD_SIM_NVBOARD_TARGET)
   find_package(SDL2_image REQUIRED)
 endif()
 find_package(CLI11 CONFIG REQUIRED)
+# TODO: Not required
+find_package(LLVM CONFIG REQUIRED)
+
+option(ENABLE_SDB "Enable simple debugger" ON)
 
 find_library(NVBOARD_LIBRARY NAMES nvboard)
 find_path(NVBOARD_INCLUDE_DIR NAMES nvboard.h)
@@ -59,6 +63,7 @@ endif()
 
 # -- Build Verilator executable and add to test
 include_directories(include)
+add_subdirectory(utils)
 
 add_subdirectory(csrc)
 
diff --git a/npc/cmake/FindReadline.cmake b/npc/cmake/FindReadline.cmake
new file mode 100644
index 0000000..dc2dd41
--- /dev/null
+++ b/npc/cmake/FindReadline.cmake
@@ -0,0 +1,49 @@
+# Code copied from sethhall@github
+#
+# - Try to find readline include dirs and libraries
+#
+# Usage of this module as follows:
+#
+#     find_package(Readline)
+#
+# Variables used by this module, they can change the default behaviour and need
+# to be set before calling find_package:
+#
+#  Readline_ROOT_DIR         Set this variable to the root installation of
+#                            readline if the module has problems finding the
+#                            proper installation path.
+#
+# Variables defined by this module:
+#
+#  READLINE_FOUND            System has readline, include and lib dirs found
+#  Readline_INCLUDE_DIR      The readline include directories.
+#  Readline_LIBRARY          The readline library.
+
+find_path(Readline_ROOT_DIR
+    NAMES include/readline/readline.h
+)
+
+find_path(Readline_INCLUDE_DIR
+    NAMES readline/readline.h
+    HINTS ${Readline_ROOT_DIR}/include
+)
+
+find_library(Readline_LIBRARY
+    NAMES readline
+    HINTS ${Readline_ROOT_DIR}/lib
+)
+
+if(Readline_INCLUDE_DIR AND Readline_LIBRARY AND Ncurses_LIBRARY)
+  set(READLINE_FOUND TRUE)
+else(Readline_INCLUDE_DIR AND Readline_LIBRARY AND Ncurses_LIBRARY)
+  find_library(Readline_LIBRARY NAMES readline)
+  include(FindPackageHandleStandardArgs)
+  find_package_handle_standard_args(Readline DEFAULT_MSG Readline_INCLUDE_DIR Readline_LIBRARY )
+  mark_as_advanced(Readline_INCLUDE_DIR Readline_LIBRARY)
+endif(Readline_INCLUDE_DIR AND Readline_LIBRARY AND Ncurses_LIBRARY)
+
+mark_as_advanced(
+    Readline_ROOT_DIR
+    Readline_INCLUDE_DIR
+    Readline_LIBRARY
+)
\ No newline at end of file
diff --git a/npc/csrc/Flow/CMakeLists.txt b/npc/csrc/Flow/CMakeLists.txt
index 606fd73..ad8d2e9 100644
--- a/npc/csrc/Flow/CMakeLists.txt
+++ b/npc/csrc/Flow/CMakeLists.txt
@@ -1,5 +1,6 @@
 include(ChiselBuild)
 add_executable(V${TOPMODULE} config.cpp main.cpp)
+target_link_libraries(V${TOPMODULE} PRIVATE disasm sdb)
 
 verilate(V${TOPMODULE} TRACE COVERAGE THREADS
   TOP_MODULE ${TOPMODULE}
@@ -8,6 +9,7 @@ verilate(V${TOPMODULE} TRACE COVERAGE THREADS
   INCLUDE_DIRS ${CHISEL_OUTPUT_DIR}
   VERILATOR_ARGS
     "--vpi"   # Enable VPI
+    "-Wno-UNOPTFLAT"
 )
 
 add_test(
diff --git a/npc/csrc/Flow/main.cpp b/npc/csrc/Flow/main.cpp
index 50eeeeb..b1c37c9 100644
--- a/npc/csrc/Flow/main.cpp
+++ b/npc/csrc/Flow/main.cpp
@@ -1,10 +1,15 @@
-#include "components.hpp"
+#include "VFlow___024root.h"
 #include "config.hpp"
+#include "disasm.hpp"
 #include "vl_wrapper.hpp"
 #include "vpi_user.h"
+#include "vpi_wrapper.hpp"
 #include <VFlow.h>
 #include <cstdint>
+#include <cstdlib>
 #include <difftest.hpp>
+#include <sdb.hpp>
+#include <types.h>
 
 using VlModule = VlModuleInterfaceCommon<VFlow>;
 using Registers = _RegistersVPI<uint32_t, 32>;
@@ -31,9 +36,10 @@ void pmem_write(int waddr, int wdata, char wmask) {
 }
 }
 
+Disassembler d{"riscv32-pc-linux-gnu"};
+
 VlModule *top;
 Registers *regs;
-using CPUState = CPUStateBase<uint32_t, 32>;
 vpiHandle pc = nullptr;
 void difftest_memcpy(paddr_t, void *, size_t, bool){};
 
@@ -58,6 +64,8 @@ void difftest_exec(uint64_t n) {
     }
   }
 }
+// std::cout << d.disassemble(top->rootp->Flow__DOT__pc__DOT__pc_reg, (uint8_t *)&top->rootp->Flow__DOT___ram_inst, 4) << std::endl;
+
 void difftest_init(int port) {
   //   top = std::make_unique<VlModule>(config.do_trace, config.wavefile);
   top = new VlModule{config.do_trace, config.wavefile};
@@ -65,20 +73,34 @@ void difftest_init(int port) {
   top->reset_eval(10);
 }
 
+DifftestInterface dut_interface = DifftestInterface{
+    &difftest_memcpy, &difftest_regcpy, &difftest_exec, &difftest_init};
+
+SDB::SDB<dut_interface> sdb_dut;
+extern "C" {
+word_t reg_str2val(const char *name, bool *success) {
+  return sdb_dut.reg_str2val(name, success);
+}
+}
+
 int main(int argc, char **argv, char **env) {
   config.cli_parse(argc, argv);
 
   /* -- Difftest -- */
   std::filesystem::path ref{config.lib_ref};
-  DifftestInterface dut_interface = DifftestInterface{
-      &difftest_memcpy, &difftest_regcpy, &difftest_exec, &difftest_init};
   DifftestInterface ref_interface = DifftestInterface{ref};
 
   Difftest<CPUStateBase<uint32_t, 32>> diff{dut_interface, ref_interface,
                                             pmem_get(), 128};
   int t = 8;
+  sdb_dut.main_loop();
   while (t--) {
-    diff.step(1);
+    if (!diff.step(1)) {
+      uint32_t pc = regs->get_pc();
+      uint32_t inst = pmem_read(pc);
+      std::cout << diff << d.disassemble(pc, (uint8_t *)&inst, 4) << std::endl;
+      return EXIT_FAILURE;
+    }
   }
 
   return 0;
diff --git a/npc/csrc/Flow/vpi_wrapper.hpp b/npc/csrc/Flow/vpi_wrapper.hpp
new file mode 100644
index 0000000..a1dd089
--- /dev/null
+++ b/npc/csrc/Flow/vpi_wrapper.hpp
@@ -0,0 +1,36 @@
+#ifndef _NPC_VPI_WRAPPER_H_
+#define _NPC_VPI_WRAPPER_H_
+#include <components.hpp>
+#include <vpi_user.h>
+
+template <typename T, std::size_t nr>
+class _RegistersVPI : public _RegistersBase<T, nr> {
+  std::array<vpiHandle, nr> reg_handles;
+  vpiHandle pc_handle;
+  T vpi_get(vpiHandle vh) {
+    s_vpi_value v;
+    v.format = vpiIntVal;
+    vpi_get_value(vh, &v);
+    return v.value.integer;
+  }
+  T fetch_pc(void) { return vpi_get(pc_handle); }
+  T fetch_reg(std::size_t id) { return vpi_get(reg_handles[id]); }
+
+public:
+  _RegistersVPI<T, nr>(const std::string regs_prefix,
+                       const std::string pcname) {
+    for (int i = 0; i < nr; i++) {
+      std::string regname = regs_prefix + std::to_string(i);
+      vpiHandle vh = vpi_handle_by_name((PLI_BYTE8 *)regname.c_str(), nullptr);
+      if (vh == nullptr) {
+        std::cerr << "vpiHandle " << regname.c_str() << " not found"
+                  << std::endl;
+        exit(EXIT_FAILURE);
+      }
+      reg_handles[i] = vh;
+    }
+    pc_handle = vpi_handle_by_name((PLI_BYTE8 *)pcname.c_str(), nullptr);
+  }
+};
+
+#endif
diff --git a/npc/csrc/Flow/components.hpp b/npc/include/components.hpp
similarity index 66%
rename from npc/csrc/Flow/components.hpp
rename to npc/include/components.hpp
index a84309a..fced1af 100644
--- a/npc/csrc/Flow/components.hpp
+++ b/npc/include/components.hpp
@@ -1,13 +1,23 @@
 
 #ifndef _NPC_COMPONENTS_H_
 #define _NPC_COMPONENTS_H_
-#include "vpi_user.h"
 #include <array>
 #include <cstdlib>
+#include <exception>
 #include <filesystem>
 #include <fstream>
 #include <iostream>
-#include <verilated_vpi.h>
+#include <map>
+#include <stdexcept>
+#include <string>
+
+const std::map<std::string, int> riscv32_regs_by_name{
+    {"$0", 0},  {"ra", 1},  {"sp", 2},   {"gp", 3},   {"tp", 4},  {"t0", 5},
+    {"t1", 6},  {"t2", 7},  {"s0", 8},   {"s1", 9},   {"a0", 10}, {"a1", 11},
+    {"a2", 12}, {"a3", 13}, {"a4", 14},  {"a5", 15},  {"a6", 16}, {"a7", 17},
+    {"s2", 18}, {"s3", 19}, {"s4", 20},  {"s5", 21},  {"s6", 22}, {"s7", 23},
+    {"s8", 24}, {"s9", 25}, {"s10", 26}, {"s11", 27}, {"t3", 28}, {"t4", 29},
+    {"t5", 30}, {"t6", 31}};
 
 template <typename T, std::size_t nr> class _RegistersBase {
   std::array<T, nr> regs;
@@ -25,36 +35,6 @@ public:
   }
 };
 
-template <typename T, std::size_t nr>
-class _RegistersVPI : public _RegistersBase<T, nr> {
-  std::array<vpiHandle, nr> reg_handles;
-  vpiHandle pc_handle;
-  T vpi_get(vpiHandle vh) {
-    s_vpi_value v;
-    v.format = vpiIntVal;
-    vpi_get_value(vh, &v);
-    return v.value.integer;
-  }
-  T fetch_pc(void) { return vpi_get(pc_handle); }
-  T fetch_reg(std::size_t id) { return vpi_get(reg_handles[id]); }
-
-public:
-  _RegistersVPI<T, nr>(const std::string regs_prefix,
-                       const std::string pcname) {
-    for (int i = 0; i < nr; i++) {
-      std::string regname = regs_prefix + std::to_string(i);
-      vpiHandle vh = vpi_handle_by_name((PLI_BYTE8 *)regname.c_str(), nullptr);
-      if (vh == nullptr) {
-        std::cerr << "vpiHandle " << regname.c_str() << " not found"
-                  << std::endl;
-        exit(EXIT_FAILURE);
-      }
-      reg_handles[i] = vh;
-    }
-    pc_handle = vpi_handle_by_name((PLI_BYTE8 *)pcname.c_str(), nullptr);
-  }
-};
-
 template <typename T, std::size_t n> class Memory {
   std::size_t addr_to_index(std::size_t addr) {
     if (addr < 0x80000000) {
@@ -74,7 +54,8 @@ template <typename T, std::size_t n> class Memory {
 public:
   std::array<T, n> mem;
   Memory(std::filesystem::path filepath, bool is_binary = true) {
-    assert(std::filesystem::exists(filepath));
+    if (!std::filesystem::exists(filepath))
+      throw std::runtime_error("Memory file not found");
     if (is_binary) {
       std::ifstream file(filepath, std::ios::binary);
       char *pmem = reinterpret_cast<char *>(mem.data());
diff --git a/npc/include/config.hpp b/npc/include/config.hpp
new file mode 100644
index 0000000..9f5873c
--- /dev/null
+++ b/npc/include/config.hpp
@@ -0,0 +1,20 @@
+#ifndef _NPC_CONFIG_H_
+#define _NPC_CONFIG_H_
+#include <CLI/App.hpp>
+#include <CLI/CLI.hpp>
+#include <CLI/Validators.hpp>
+#include <filesystem>
+
+struct Config {
+  std::filesystem::path memory_file;
+  uint64_t max_sim_time = 1000;
+  bool memory_file_binary = {true};
+  bool do_trace{false};
+  std::filesystem::path wavefile;
+  std::filesystem::path lib_ref;
+  void cli_parse(int argc, char **argv);
+};
+
+extern Config config;
+
+#endif
\ No newline at end of file
diff --git a/npc/include/difftest.hpp b/npc/include/difftest.hpp
index dd690b9..7349004 100644
--- a/npc/include/difftest.hpp
+++ b/npc/include/difftest.hpp
@@ -1,12 +1,14 @@
 #ifndef _DIFFTEST_DIFFTEST_H_
 #define _DIFFTEST_DIFFTEST_H_
 #include <cassert>
+#include <components.hpp>
 #include <cstdint>
 #include <cstdlib>
 #include <dlfcn.h>
 #include <filesystem>
 #include <functional>
 #include <iostream>
+#include <map>
 #include <memory>
 
 using paddr_t = uint32_t;
@@ -69,14 +71,11 @@ public:
     dut.regcpy(dut_state.get(), DIFFTEST_FROM_REF);
   }
 
-  void step(uint64_t n) {
+  bool step(uint64_t n) {
     ref.exec(n);
     dut.exec(n);
     fetch_state();
-    if (*ref_state != *dut_state) {
-      std::cout << *this;
-      exit(EXIT_FAILURE);
-    }
+    return *ref_state == *dut_state;
   }
 
   friend std::ostream &operator<<(std::ostream &os, const Difftest<S> &d) {
@@ -90,6 +89,8 @@ public:
 template <typename R, size_t nr_reg> struct CPUStateBase {
   R reg[nr_reg] = {0};
   paddr_t pc = 0x80000000;
+  static const std::map<std::string, int> inline regs_by_name =
+      riscv32_regs_by_name;
   CPUStateBase() {
     for (int i = 0; i < nr_reg; i++)
       reg[i] = 0;
@@ -106,6 +107,9 @@ template <typename R, size_t nr_reg> struct CPUStateBase {
   bool operator!=(const CPUStateBase &other) const {
     return !(*this == other); // Reuse the == operator for != implementation
   }
+
+  /* This does not update the register!!! */
+  R at(std::string name) { return reg[regs_by_name.at(name)]; }
 };
 
 template <typename R, size_t nr_reg>
diff --git a/npc/include/types.h b/npc/include/types.h
new file mode 100644
index 0000000..f6a8d87
--- /dev/null
+++ b/npc/include/types.h
@@ -0,0 +1,23 @@
+#ifndef _NPC_TYPES_H__
+#define _NPC_TYPES_H__
+#include <inttypes.h>
+
+typedef uint32_t word_t;
+typedef int32_t sword_t;
+static const word_t WORD_T_MAX = UINT32_MAX;
+static const sword_t SWORD_T_MAX = INT32_MAX;
+static const sword_t SWORD_T_MIN = INT32_MIN;
+#define WORD_BYTES 4
+
+#define FMT_WORD "0x%08x"
+typedef uint32_t vaddr_t;
+typedef uint32_t paddr_t;
+#define FMT_ADDR "0x%08x"
+typedef uint16_t ioaddr_t;
+
+#ifdef __cplusplus
+#include <difftest.hpp>
+using CPUState = CPUStateBase<word_t, 32>;
+#endif
+
+#endif
\ No newline at end of file
diff --git a/npc/include/vl_wrapper.hpp b/npc/include/vl_wrapper.hpp
new file mode 100644
index 0000000..4d42b55
--- /dev/null
+++ b/npc/include/vl_wrapper.hpp
@@ -0,0 +1,65 @@
+#ifndef _NPC_TRACER_H_
+#define _NPC_TRACER_H_
+#include <filesystem>
+#include <verilated_vcd_c.h>
+
+template <class T> class Tracer {
+  std::shared_ptr<T> top;
+  std::unique_ptr<VerilatedVcdC> m_trace;
+  uint64_t cycle = 0;
+
+public:
+  Tracer(T *top, std::filesystem::path wavefile) {
+    top = top;
+    Verilated::traceEverOn(true);
+    m_trace = std::make_unique<VerilatedVcdC>();
+    top->trace(m_trace.get(), 5);
+    m_trace->open(wavefile.c_str());
+  }
+  ~Tracer() { m_trace->close(); }
+
+  /**
+   * Dump signals to waveform file. Must be called once after every top->eval()
+   * call.
+   */
+  void update() { m_trace->dump(cycle++); }
+};
+
+template <typename T> class VlModuleInterfaceCommon : public T {
+  uint64_t sim_time = 0;
+  uint64_t posedge_cnt = 0;
+  std::unique_ptr<Tracer<T>> tracer;
+
+public:
+  VlModuleInterfaceCommon<T>(bool do_trace,
+                             std::filesystem::path wavefile = "waveform.vcd") {
+    if (do_trace)
+      tracer = std::make_unique<Tracer<T>>(this, wavefile);
+  }
+  void eval() {
+    if (this->is_posedge()) {
+      posedge_cnt++;
+    }
+    T::clock = !T::clock;
+    sim_time++;
+    T::eval();
+    if (tracer)
+      tracer->update();
+  }
+  void eval(int n) {
+    for (int i = 0; i < n; i++) {
+      this->eval();
+    }
+  }
+  void reset_eval(int n) {
+    this->reset = 1;
+    this->eval(n);
+    this->reset = 0;
+  }
+  bool is_posedge() {
+    // Will be posedge when eval is called
+    return T::clock == 0;
+  }
+};
+
+#endif
diff --git a/npc/utils/CMakeLists.txt b/npc/utils/CMakeLists.txt
new file mode 100644
index 0000000..017313c
--- /dev/null
+++ b/npc/utils/CMakeLists.txt
@@ -0,0 +1,4 @@
+add_subdirectory(disasm)
+if (ENABLE_SDB)
+  add_subdirectory(sdb)
+endif()
diff --git a/npc/utils/disasm/CMakeLists.txt b/npc/utils/disasm/CMakeLists.txt
new file mode 100644
index 0000000..e019bf7
--- /dev/null
+++ b/npc/utils/disasm/CMakeLists.txt
@@ -0,0 +1,4 @@
+add_library(disasm disasm.cpp)
+target_include_directories(disasm PUBLIC include)
+llvm_map_components_to_libnames(LLVM_LIBS ${LLVM_TARGETS_TO_BUILD})
+target_link_libraries(disasm PUBLIC ${LLVM_LIBS})
diff --git a/npc/utils/disasm/disasm.cpp b/npc/utils/disasm/disasm.cpp
new file mode 100644
index 0000000..0e817ba
--- /dev/null
+++ b/npc/utils/disasm/disasm.cpp
@@ -0,0 +1,87 @@
+#include <disasm.hpp>
+#include <llvm/MC/MCAsmInfo.h>
+#include <llvm/MC/MCContext.h>
+#include <llvm/MC/MCDisassembler/MCDisassembler.h>
+#include <llvm/MC/MCInstPrinter.h>
+#include <llvm/Support/raw_ostream.h>
+#if LLVM_VERSION_MAJOR >= 14
+#include <llvm/MC/TargetRegistry.h>
+#if LLVM_VERSION_MAJOR >= 15
+#include <llvm/MC/MCSubtargetInfo.h>
+#endif
+#else
+#include <llvm/Support/TargetRegistry.h>
+#endif
+#include <iostream>
+#include <llvm/Support/TargetSelect.h>
+#include <sstream>
+
+#if defined(__GNUC__) && !defined(__clang__)
+#pragma GCC diagnostic pop
+#endif
+
+#if LLVM_VERSION_MAJOR < 11
+#error Please use LLVM with major version >= 11
+#endif
+
+Disassembler::Disassembler(std::string triple) : triple(triple) {
+  llvm::InitializeAllTargetInfos();
+  llvm::InitializeAllTargetMCs();
+  llvm::InitializeAllAsmParsers();
+  llvm::InitializeAllDisassemblers();
+
+  std::string errstr;
+
+  llvm::MCInstrInfo *gMII = nullptr;
+  llvm::MCRegisterInfo *gMRI = nullptr;
+  auto target = llvm::TargetRegistry::lookupTarget(triple, errstr);
+  if (!target) {
+    llvm::errs() << "Can't find target for " << triple << ": " << errstr
+                 << "\n";
+    assert(0);
+  }
+
+  llvm::MCTargetOptions MCOptions;
+  gSTI = target->createMCSubtargetInfo(triple, "", "");
+  std::string isa = target->getName();
+  if (isa == "riscv32" || isa == "riscv64") {
+    gSTI->ApplyFeatureFlag("+m");
+    gSTI->ApplyFeatureFlag("+a");
+    gSTI->ApplyFeatureFlag("+c");
+    gSTI->ApplyFeatureFlag("+f");
+    gSTI->ApplyFeatureFlag("+d");
+  }
+  gMII = target->createMCInstrInfo();
+  gMRI = target->createMCRegInfo(triple);
+  auto AsmInfo = target->createMCAsmInfo(*gMRI, triple, MCOptions);
+#if LLVM_VERSION_MAJOR >= 13
+  auto llvmTripleTwine = llvm::Twine(triple);
+  auto llvmtriple = llvm::Triple(llvmTripleTwine);
+  auto Ctx = new llvm::MCContext(llvmtriple, AsmInfo, gMRI, nullptr);
+#else
+  auto Ctx = new llvm::MCContext(AsmInfo, gMRI, nullptr);
+#endif
+  gDisassembler = target->createMCDisassembler(*gSTI, *Ctx);
+  gIP = target->createMCInstPrinter(llvm::Triple(triple),
+                                    AsmInfo->getAssemblerDialect(), *AsmInfo,
+                                    *gMII, *gMRI);
+  gIP->setPrintImmHex(true);
+  gIP->setPrintBranchImmAsAddress(true);
+  if (isa == "riscv32" || isa == "riscv64")
+    gIP->applyTargetSpecificCLOption("no-aliases");
+}
+
+std::string Disassembler::disassemble(uint64_t pc, uint8_t *code, int nbyte) {
+  llvm::MCInst inst;
+  llvm::ArrayRef<uint8_t> arr(code, nbyte);
+  uint64_t dummy_size = 0;
+  gDisassembler->getInstruction(inst, dummy_size, arr, pc, llvm::nulls());
+
+  std::stringstream ss;
+  ss << "0x" << std::hex << pc << ": ";
+  std::string s = ss.str();
+  llvm::raw_string_ostream os{s};
+  gIP->printInst(&inst, pc, "", *gSTI, os);
+
+  return s;
+}
diff --git a/npc/utils/disasm/include/disasm.hpp b/npc/utils/disasm/include/disasm.hpp
new file mode 100644
index 0000000..a14ebb3
--- /dev/null
+++ b/npc/utils/disasm/include/disasm.hpp
@@ -0,0 +1,17 @@
+#ifndef _NPC_UTILS_DISASM_
+#define _NPC_UTILS_DISASM_
+#include "llvm/MC/MCDisassembler/MCDisassembler.h"
+#include "llvm/MC/MCInstPrinter.h"
+
+class Disassembler {
+  llvm::MCDisassembler *gDisassembler = nullptr;
+  llvm::MCSubtargetInfo *gSTI = nullptr;
+  llvm::MCInstPrinter *gIP = nullptr;
+  std::string triple;
+
+public:
+  Disassembler(std::string);
+  std::string disassemble(uint64_t pc, uint8_t *code, int nbyte);
+};
+
+#endif
\ No newline at end of file
diff --git a/npc/utils/sdb/CMakeLists.txt b/npc/utils/sdb/CMakeLists.txt
new file mode 100644
index 0000000..6b1cb2c
--- /dev/null
+++ b/npc/utils/sdb/CMakeLists.txt
@@ -0,0 +1,14 @@
+find_package(Readline REQUIRED)
+find_package(FLEX REQUIRED)
+find_package(BISON REQUIRED)
+set(PARSER_DIR "${CMAKE_CURRENT_BINARY_DIR}")
+set(LEXER_OUT "${PARSER_DIR}/lexer.c")
+set(PARSER_OUT "${PARSER_DIR}/parser.c")
+flex_target(LEXER addrexp.l "${LEXER_OUT}" DEFINES_FILE "${PARSER_DIR}/addrexp_lex.h")
+bison_target(PARSER addrexp.y "${PARSER_OUT}" DEFINES_FILE "${PARSER_DIR}/addrexp.h")
+add_flex_bison_dependency(LEXER PARSER)
+
+add_library(sdb sdb.cpp console.cpp "${LEXER_OUT}" "${PARSER_OUT}")
+target_link_libraries(sdb PRIVATE ${Readline_LIBRARY})
+target_include_directories(sdb PRIVATE ${Readline_INCLUDE_DIR})
+target_include_directories(sdb PUBLIC include)
diff --git a/npc/utils/sdb/addrexp.l b/npc/utils/sdb/addrexp.l
new file mode 100644
index 0000000..d81f0e1
--- /dev/null
+++ b/npc/utils/sdb/addrexp.l
@@ -0,0 +1,26 @@
+%{
+    #include <types.h>
+    #include <stdbool.h>
+    #include "addrexp.h"
+    static bool success = false;
+    void yyerror(word_t *result, const char *err);
+    word_t reg_str2val(const char *name, bool*);
+%}
+%option noyywrap
+
+%%
+
+0[xX][0-9a-fA-F]+ { yylval = strtoul(yytext, NULL, 16); return HEX_NUMBER; }
+[0-9]+            { yylval = strtoul(yytext, NULL, 10); return NUMBER; }
+$[asgprt$][0-9pa][0-9]?    {
+    yylval = reg_str2val(yytext + 1, &success);
+    if(!success) {
+        yyerror(NULL, "Failed to convert reg to value");
+        return YYerror;
+    }
+    return REGISTER;
+}
+[+\-*/<=()]         { return *yytext; }
+[ \t]             {  }
+.                 { printf("Unexpected character: %s\n", yytext); return YYerror; }
+%%
diff --git a/npc/utils/sdb/addrexp.y b/npc/utils/sdb/addrexp.y
new file mode 100644
index 0000000..ca1a5c9
--- /dev/null
+++ b/npc/utils/sdb/addrexp.y
@@ -0,0 +1,58 @@
+%code requires {
+    #include <types.h>
+    #include <stdio.h>
+    #include <stdlib.h>
+    extern int yylex(void);
+}
+%{
+    #include <types.h>
+    #include <stdio.h>
+    #include <stdlib.h>
+    void yyerror(word_t *result, const char *err) {
+      fprintf(stderr, "%s", err);
+    }
+    int pmem_read(int raddr);
+%}
+
+%token NUMBER HEX_NUMBER
+%token REGISTER
+%locations
+%start input
+%define api.value.type { word_t }
+%parse-param { uint32_t *result }
+%left '-' '+'
+%left '*' '/'
+
+%%
+input
+    : expression { *result = $1; }
+    ;
+
+expression
+    : number { $$ = $1; }
+    | expression '>' '=' expression { $$ = ($1 >= $4); }
+    | expression '<' '=' expression { $$ = ($1 <= $4); }
+    | expression '=' '=' expression { $$ = ($1 == $4); }
+    | expression '!' '=' expression { $$ = ($1 == $4); }
+    | expression '>' expression { $$ = ($1 > $3); }
+    | expression '<' expression { $$ = ($1 < $3); }
+    | expression '+' expression { $$ = $1 + $3; }
+    | expression '-' expression { $$ = $1 - $3; }
+    | expression '*' expression { $$ = $1 * $3; }
+    | expression '/' expression {
+        if($3 == 0) {
+          fprintf(stderr, "Error: divide by zero at" FMT_WORD " / " FMT_WORD "\n", $1, $3);
+          YYABORT;
+        };
+        $$ = $1 / $3;
+      }
+    | '-' number { $$ = -$2; }
+    | '*' expression { $$ = pmem_read($2); }
+    | '(' expression ')' { $$ = $2; }
+
+number
+    : REGISTER
+    | NUMBER
+    | HEX_NUMBER
+
+%%
diff --git a/npc/utils/sdb/console.cpp b/npc/utils/sdb/console.cpp
new file mode 100644
index 0000000..485e192
--- /dev/null
+++ b/npc/utils/sdb/console.cpp
@@ -0,0 +1,215 @@
+// cpp-readline library
+//
+// @author zmij
+// @date Nov 30, 2015
+
+#include <console.hpp>
+
+#include <algorithm>
+#include <fstream>
+#include <functional>
+#include <iostream>
+#include <iterator>
+#include <sstream>
+#include <unordered_map>
+
+#include <cstdlib>
+#include <cstring>
+#include <readline/history.h>
+#include <readline/readline.h>
+
+namespace CppReadline {
+namespace {
+
+Console *currentConsole = nullptr;
+HISTORY_STATE *emptyHistory = history_get_history_state();
+
+} /* namespace  */
+
+struct Console::Impl {
+  using RegisteredCommands =
+      std::unordered_map<std::string, Console::CommandFunction>;
+
+  ::std::string greeting_;
+  // These are hardcoded commands. They do not do anything and are catched manually in the executeCommand function.
+  RegisteredCommands commands_;
+  HISTORY_STATE *history_ = nullptr;
+
+  Impl(::std::string const &greeting) : greeting_(greeting), commands_() {}
+  ~Impl() { free(history_); }
+
+  Impl(Impl const &) = delete;
+  Impl(Impl &&) = delete;
+  Impl &operator=(Impl const &) = delete;
+  Impl &operator=(Impl &&) = delete;
+};
+
+// Here we set default commands, they do nothing since we quit with them
+// Quitting behaviour is hardcoded in readLine()
+Console::Console(std::string const &greeting) : pimpl_{new Impl{greeting}} {
+  // Init readline basics
+  rl_attempted_completion_function = &Console::getCommandCompletions;
+
+  // These are default hardcoded commands.
+  // Help command lists available commands.
+  pimpl_->commands_["help"] = [this](const Arguments &) {
+    auto commands = getRegisteredCommands();
+    std::cout << "Available commands are:\n";
+    for (auto &command : commands)
+      std::cout << "\t" << command << "\n";
+    return ReturnCode::Ok;
+  };
+  // Run command executes all commands in an external file.
+  pimpl_->commands_["run"] = [this](const Arguments &input) {
+    if (input.size() < 2) {
+      std::cout << "Usage: " << input[0] << " script_filename\n";
+      return 1;
+    }
+    return executeFile(input[1]);
+  };
+  // Quit and Exit simply terminate the console.
+  pimpl_->commands_["quit"] = [this](const Arguments &) {
+    return ReturnCode::Quit;
+  };
+
+  pimpl_->commands_["exit"] = [this](const Arguments &) {
+    return ReturnCode::Quit;
+  };
+}
+
+Console::~Console() = default;
+
+void Console::registerCommand(const std::string &s, CommandFunction f) {
+  pimpl_->commands_[s] = f;
+}
+
+std::vector<std::string> Console::getRegisteredCommands() const {
+  std::vector<std::string> allCommands;
+  for (auto &pair : pimpl_->commands_)
+    allCommands.push_back(pair.first);
+
+  return allCommands;
+}
+
+void Console::saveState() {
+  free(pimpl_->history_);
+  pimpl_->history_ = history_get_history_state();
+}
+
+void Console::reserveConsole() {
+  if (currentConsole == this)
+    return;
+
+  // Save state of other Console
+  if (currentConsole)
+    currentConsole->saveState();
+
+  // Else we swap state
+  if (!pimpl_->history_)
+    history_set_history_state(emptyHistory);
+  else
+    history_set_history_state(pimpl_->history_);
+
+  // Tell others we are using the console
+  currentConsole = this;
+}
+
+void Console::setGreeting(const std::string &greeting) {
+  pimpl_->greeting_ = greeting;
+}
+
+std::string Console::getGreeting() const { return pimpl_->greeting_; }
+
+int Console::executeCommand(const std::string &command) {
+  // Convert input to vector
+  std::vector<std::string> inputs;
+  {
+    std::istringstream iss(command);
+    std::copy(std::istream_iterator<std::string>(iss),
+              std::istream_iterator<std::string>(), std::back_inserter(inputs));
+  }
+
+  if (inputs.size() == 0)
+    return ReturnCode::Ok;
+
+  Impl::RegisteredCommands::iterator it;
+  if ((it = pimpl_->commands_.find(inputs[0])) != end(pimpl_->commands_)) {
+    return static_cast<int>((it->second)(inputs));
+  }
+
+  std::cout << "Command '" << inputs[0] << "' not found.\n";
+  return ReturnCode::Error;
+}
+
+int Console::executeFile(const std::string &filename) {
+  std::ifstream input(filename);
+  if (!input) {
+    std::cout << "Could not find the specified file to execute.\n";
+    return ReturnCode::Error;
+  }
+  std::string command;
+  int counter = 0, result;
+
+  while (std::getline(input, command)) {
+    if (command[0] == '#')
+      continue; // Ignore comments
+    // Report what the Console is executing.
+    std::cout << "[" << counter << "] " << command << '\n';
+    if ((result = executeCommand(command)))
+      return result;
+    ++counter;
+    std::cout << '\n';
+  }
+
+  // If we arrived successfully at the end, all is ok
+  return ReturnCode::Ok;
+}
+
+int Console::readLine() {
+  reserveConsole();
+
+  char *buffer = readline(pimpl_->greeting_.c_str());
+  if (!buffer) {
+    std::cout
+        << '\n'; // EOF doesn't put last endline so we put that so that it looks uniform.
+    return ReturnCode::Quit;
+  }
+
+  // TODO: Maybe add commands to history only if succeeded?
+  if (buffer[0] != '\0')
+    add_history(buffer);
+
+  std::string line(buffer);
+  free(buffer);
+
+  return executeCommand(line);
+}
+
+char **Console::getCommandCompletions(const char *text, int start, int) {
+  char **completionList = nullptr;
+
+  if (start == 0)
+    completionList = rl_completion_matches(text, &Console::commandIterator);
+
+  return completionList;
+}
+
+char *Console::commandIterator(const char *text, int state) {
+  static Impl::RegisteredCommands::iterator it;
+  if (!currentConsole)
+    return nullptr;
+  auto &commands = currentConsole->pimpl_->commands_;
+
+  if (state == 0)
+    it = begin(commands);
+
+  while (it != end(commands)) {
+    auto &command = it->first;
+    ++it;
+    if (command.find(text) != std::string::npos) {
+      return strdup(command.c_str());
+    }
+  }
+  return nullptr;
+}
+} // namespace CppReadline
diff --git a/npc/utils/sdb/include/console.hpp b/npc/utils/sdb/include/console.hpp
new file mode 100644
index 0000000..538ce2f
--- /dev/null
+++ b/npc/utils/sdb/include/console.hpp
@@ -0,0 +1,145 @@
+// cpp-readline library
+//
+// @author zmij
+// @date Nov 30, 2015
+
+#ifndef CONSOLE_CONSOLE_HEADER_FILE
+#define CONSOLE_CONSOLE_HEADER_FILE
+
+#include <functional>
+#include <memory>
+#include <string>
+#include <vector>
+
+namespace CppReadline {
+class Console {
+public:
+  /**
+    * @brief This is the function type that is used to interface with the Console class.
+    *
+    * These are the functions that are going to get called by Console
+    * when the user types in a message. The vector will hold the
+    * command elements, and the function needs to return its result.
+    * The result can either be Quit (-1), OK (0), or an arbitrary
+    * error (>=1).
+    */
+  using Arguments = std::vector<std::string>;
+  using CommandFunction = std::function<int(const Arguments &)>;
+
+  enum ReturnCode {
+    Quit = -1,
+    Ok = 0,
+    Error = 1 // Or greater!
+  };
+
+  /**
+    * @brief Basic constructor.
+    *
+    * The Console comes with two predefined commands: "quit" and
+    * "exit", which both terminate the console, "help" which prints a
+    * list of all registered commands, and "run" which executes script
+    * files.
+    *
+    * These commands can be overridden or unregistered - but remember
+    * to leave at least one to quit ;).
+    *
+    * @param greeting This represents the prompt of the Console.
+    */
+  explicit Console(std::string const &greeting);
+
+  /**
+    * @brief Basic destructor.
+    *
+    * Frees the history which is been produced by GNU readline.
+    */
+  ~Console();
+
+  /**
+    * @brief This function registers a new command within the Console.
+    *
+    * If the command already existed, it overwrites the previous entry.
+    *
+    * @param s The name of the command as inserted by the user.
+    * @param f The function that will be called once the user writes the command.
+    */
+  void registerCommand(const std::string &s, CommandFunction f);
+
+  /**
+    * @brief This function returns a list with the currently available commands.
+    *
+    * @return A vector containing all registered commands names.
+    */
+  std::vector<std::string> getRegisteredCommands() const;
+
+  /**
+    * @brief Sets the prompt for this Console.
+    *
+    * @param greeting The new greeting.
+    */
+  void setGreeting(const std::string &greeting);
+
+  /**
+    * @brief Gets the current prompt of this Console.
+    *
+    * @return The currently set greeting.
+    */
+  std::string getGreeting() const;
+
+  /**
+    * @brief This function executes an arbitrary string as if it was inserted via stdin.
+    *
+    * @param command The command that needs to be executed.
+    *
+    * @return The result of the operation.
+    */
+  int executeCommand(const std::string &command);
+
+  /**
+    * @brief This function calls an external script and executes all commands inside.
+    *
+    * This function stops execution as soon as any single command returns something
+    * different from 0, be it a quit code or an error code.
+    *
+    * @param filename The pathname of the script.
+    *
+    * @return What the last command executed returned.
+    */
+  int executeFile(const std::string &filename);
+
+  /**
+    * @brief This function executes a single command from the user via stdin.
+    *
+    * @return The result of the operation.
+    */
+  int readLine();
+
+private:
+  Console(const Console &) = delete;
+  Console(Console &&) = delete;
+  Console &operator=(Console const &) = delete;
+  Console &operator=(Console &&) = delete;
+
+  struct Impl;
+  using PImpl = ::std::unique_ptr<Impl>;
+  PImpl pimpl_;
+
+  /**
+    * @brief This function saves the current state so that some other Console can make use of the GNU readline facilities.
+    */
+  void saveState();
+  /**
+    * @brief This function reserves the use of the GNU readline facilities to the calling Console instance.
+    */
+  void reserveConsole();
+
+  // GNU newline interface to our commands.
+  using commandCompleterFunction = char **(const char *text, int start,
+                                           int end);
+  using commandIteratorFunction = char *(const char *text, int state);
+
+  static commandCompleterFunction getCommandCompletions;
+  static commandIteratorFunction commandIterator;
+};
+} // namespace CppReadline
+
+#endif
diff --git a/npc/utils/sdb/include/sdb.hpp b/npc/utils/sdb/include/sdb.hpp
new file mode 100644
index 0000000..18aae8a
--- /dev/null
+++ b/npc/utils/sdb/include/sdb.hpp
@@ -0,0 +1,149 @@
+#ifndef _SDB_SDB_HEADER_FILE_
+#define _SDB_SDB_HEADER_FILE_
+
+#include <components.hpp>
+#include <console.hpp>
+#include <difftest.hpp>
+#include <memory>
+#include <stdexcept>
+#include <types.h>
+
+namespace cr = CppReadline;
+using ret = cr::Console::ReturnCode;
+
+namespace SDB {
+
+enum SDBStatus {
+  SDB_SUCCESS,
+  SDB_WRONG_ARGUMENT,
+};
+
+struct Handler {
+  const std::vector<const char *> names;
+  cr::Console::CommandFunction f;
+};
+
+template <const DifftestInterface &funcs> class _SDBHandlers {
+  using CPUState = CPUStateBase<uint32_t, 32>;
+
+private:
+  std::vector<Handler> all_handlers;
+
+public:
+  static CPUState cpu;
+
+private:
+  static _SDBHandlers<funcs> *instance;
+  static int cmd_continue(const cr::Console::Arguments &input);
+  static int cmd_step(const std::vector<std::string> &input);
+  static int cmd_info_registers(const std::vector<std::string> &input);
+  static int cmd_print(const std::vector<std::string> &input);
+  _SDBHandlers<funcs>(std::vector<Handler> all_handlers)
+      : all_handlers(all_handlers){};
+
+public:
+  _SDBHandlers<funcs>(const _SDBHandlers<funcs> &) = delete;
+  _SDBHandlers<funcs> operator=(const _SDBHandlers<funcs> &) = delete;
+
+  static _SDBHandlers<funcs> *getInstance() {
+    if (instance == nullptr) {
+      std::vector<Handler> all_handlers{
+          Handler{{"c", "continue"}, &_SDBHandlers::cmd_continue},
+          Handler{{"si", "step-instruction"}, &_SDBHandlers::cmd_step},
+      };
+      instance = new _SDBHandlers<funcs>(all_handlers);
+    }
+    return instance;
+  }
+
+  void registerHandlers(cr::Console *c);
+};
+
+template <const DifftestInterface &funcs>
+_SDBHandlers<funcs> *_SDBHandlers<funcs>::instance = nullptr;
+
+template <const DifftestInterface &funcs>
+CPUState _SDBHandlers<funcs>::cpu = CPUState();
+
+template <const DifftestInterface &funcs>
+int _SDBHandlers<funcs>::cmd_continue(const cr::Console::Arguments &input) {
+  if (input.size() > 1)
+    return SDB_WRONG_ARGUMENT;
+  funcs.exec(-1);
+  return SDB_SUCCESS;
+}
+
+template <const DifftestInterface &funcs>
+int _SDBHandlers<funcs>::cmd_step(const std::vector<std::string> &input) {
+  if (input.size() > 2) {
+    return SDB_WRONG_ARGUMENT;
+  }
+  uint64_t step_count = input.size() == 2 ? std::stoull(input[1]) : 1;
+  funcs.exec(step_count);
+  return SDB_SUCCESS;
+}
+
+template <const DifftestInterface &funcs>
+int _SDBHandlers<funcs>::cmd_info_registers(
+    const std::vector<std::string> &input) {
+  if (input.size() > 1)
+    return SDB_WRONG_ARGUMENT;
+  std::cout << _SDBHandlers<funcs>::getInstance()->cpu << std::endl;
+  return SDB_SUCCESS;
+}
+
+template <const DifftestInterface &funcs>
+int _SDBHandlers<funcs>::cmd_print(const std::vector<std::string> &input) {
+  exit(1);
+}
+
+template <const DifftestInterface &funcs>
+void _SDBHandlers<funcs>::registerHandlers(cr::Console *c) {
+  for (auto &h : this->all_handlers) {
+    for (auto &name : h.names) {
+      c->registerCommand(name, h.f);
+    }
+  }
+}
+
+template <const DifftestInterface &funcs> class SDB {
+private:
+  std::unique_ptr<CppReadline::Console> c;
+  using SDBHandlers = _SDBHandlers<funcs>;
+
+public:
+  SDB(std::string const &greeting = "\033[1;34m(npc)\033[0m ") {
+    c = std::make_unique<CppReadline::Console>(greeting);
+    SDBHandlers::getInstance()->registerHandlers(c.get());
+  };
+
+  word_t reg_str2val(const char *name, bool *success) {
+    try {
+      *success = true;
+      return SDBHandlers::getInstance()->cpu.at(name);
+    } catch (std::runtime_error) {
+      *success = false;
+      return 0;
+    }
+  }
+
+  int main_loop() {
+    int retCode;
+    do {
+      retCode = c->readLine();
+      // We can also change the prompt based on last return value:
+      if (retCode == ret::Ok)
+        c->setGreeting("\033[1;34m(npc)\033[0m ");
+      else
+        c->setGreeting("\033[1;31m(npc)\033[0m ");
+
+      if (retCode == SDB_WRONG_ARGUMENT) {
+        std::cout << "Wrong argument give to command\n";
+      }
+    } while (retCode != ret::Quit);
+    return 0;
+  }
+};
+} // namespace SDB
+
+#endif
\ No newline at end of file
diff --git a/npc/utils/sdb/sdb.cpp b/npc/utils/sdb/sdb.cpp
new file mode 100644
index 0000000..9bfa6b5
--- /dev/null
+++ b/npc/utils/sdb/sdb.cpp
@@ -0,0 +1,10 @@
+#include <components.hpp>
+#include <console.hpp>
+#include <difftest.hpp>
+#include <sdb.hpp>
+#include <types.h>
+
+namespace cr = CppReadline;
+using ret = cr::Console::ReturnCode;
+
+namespace SDB {}