diff --git a/Makefile b/Makefile
index 6e42c0d06..8d4a972e2 100644
--- a/Makefile
+++ b/Makefile
@@ -28,6 +28,7 @@ BUILD_DIR  = $(DESIGN_DIR)/build
 RTL_DIR = $(BUILD_DIR)/rtl
 RTL_SUFFIX ?= sv
 SIM_TOP_V = $(RTL_DIR)/$(SIM_TOP).$(RTL_SUFFIX)
+SIM_TOP_FIR = $(RTL_DIR)/$(SIM_TOP).fir
 
 # generate difftest files for non-chisel design.
 .DEFAULT_GOAL := difftest_verilog
@@ -228,6 +229,7 @@ SIM_CXXFLAGS += -Werror
 endif
 
 include verilator.mk
+include gsim.mk
 include vcs.mk
 include palladium.mk
 include libso.mk
diff --git a/gsim.mk b/gsim.mk
new file mode 100644
index 000000000..ff55213f5
--- /dev/null
+++ b/gsim.mk
@@ -0,0 +1,37 @@
+#***************************************************************************************
+# Copyright (c) 2024 Beijing Institute of Open Source Chip (BOSC)
+# Copyright (c) 2020-2024 Institute of Computing Technology, Chinese Academy of Sciences
+#
+# DiffTest is licensed under Mulan PSL v2.
+# You can use this software according to the terms and conditions of the Mulan PSL v2.
+# You may obtain a copy of Mulan PSL v2 at:
+#          http://license.coscl.org.cn/MulanPSL2
+#
+# THIS SOFTWARE IS PROVIDED ON AN "AS IS" BASIS, WITHOUT WARRANTIES OF ANY KIND,
+# EITHER EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO NON-INFRINGEMENT,
+# MERCHANTABILITY OR FIT FOR A PARTICULAR PURPOSE.
+#
+# See the Mulan PSL v2 for more details.
+#***************************************************************************************
+
+GSIM_TOP       = SimTop
+GSIM_TARGET    = $(abspath $(BUILD_DIR)/gsim)
+GSIM_BUILD_DIR = $(abspath $(BUILD_DIR)/gsim-compile)
+
+GSIM_CSRC_DIR   = $(abspath ./src/test/csrc/verilator)
+GSIM_CONFIG_DIR = $(abspath ./config)
+
+GSIM_CXXFILES  = $(SIM_CXXFILES) $(shell find $(GSIM_CSRC_DIR) -name "*.cpp")
+GSIM_CXXFLAGS  = $(SIM_CXXFLAGS) -I$(GSIM_CSRC_DIR) -DNUM_CORES=$(NUM_CORES) -DGSIM
+GSIM_LDFLAGS   = $(SIM_LDFLAGS) -ldl
+
+GSIM_HOME := $(abspath $(GSIM_HOME))
+
+$(GSIM_TARGET):
+ifndef GSIM_HOME
+	$(error GSIM_HOME is not set, please set manually)
+endif
+	# make -C $(GSIM_HOME) compile BUILD_DIR=$(GSIM_BUILD_DIR) NAME=$(GSIM_TOP) FIRRTL_FILE=$(SIM_TOP_FIR)
+	make -C $(GSIM_HOME) build-emu BUILD_DIR=$(GSIM_BUILD_DIR) NAME=$(GSIM_TOP) target=$(GSIM_TARGET) GSIM_CXXFILES="$(GSIM_CXXFILES)" GSIM_CXXFLAGS="$(GSIM_CXXFLAGS)" GSIM_LDFLAGS="$(GSIM_LDFLAGS)"
+
+gsim: $(GSIM_TARGET)
diff --git a/src/test/csrc/common/main.cpp b/src/test/csrc/common/main.cpp
index 971d7f72c..9730629a2 100644
--- a/src/test/csrc/common/main.cpp
+++ b/src/test/csrc/common/main.cpp
@@ -17,7 +17,7 @@
 #include "common.h"
 #include "dut.h"
 
-#ifdef VERILATOR
+#if defined(VERILATOR) || defined(GSIM)
 #include "emu.h"
 #define DUT_MODEL Emulator
 #endif
diff --git a/src/test/csrc/verilator/emu.cpp b/src/test/csrc/verilator/emu.cpp
index 917acba65..7d5bbd587 100644
--- a/src/test/csrc/verilator/emu.cpp
+++ b/src/test/csrc/verilator/emu.cpp
@@ -325,13 +325,16 @@ inline EmuArgs parse_args(int argc, const char *argv[]) {
   args.ipc_file = fopen(ipc_file, "w");
 #endif
 
+#ifdef VERILATOR
   Verilated::commandArgs(argc, argv); // Prepare extra args for TLMonitor
+#endif
   return args;
 }
 
 Emulator::Emulator(int argc, const char *argv[])
-    : dut_ptr(new VSimTop), cycles(0), trapCode(STATE_RUNNING), elapsed_time(uptime()) {
+    : dut_ptr(new DUT_TOP), cycles(0), trapCode(STATE_RUNNING), elapsed_time(uptime()) {
 
+#ifdef VERILATOR
 #if !defined(VERILATOR_VERSION_INTEGER) || VERILATOR_VERSION_INTEGER < 5026000
   // Large designs may cause segmentation fault due to stack overflow.
   // Legacy versions of Verilator do not automatically set the stack size.
@@ -344,17 +347,20 @@ Emulator::Emulator(int argc, const char *argv[])
     printf("[warning] cannot set stack size. Large designs may cause SIGSEGV.\n");
   }
 #endif
+#endif // VERILATOR
 
   args = parse_args(argc, argv);
 #ifdef ENABLE_CONSTANTIN
   void constantinLoad();
   constantinLoad();
 #endif // CONSTANTIN
+#ifdef VERILATOR
   // srand
   srand(args.seed);
   srand48(args.seed);
   Verilated::randSeed(args.seed);
   Verilated::randReset(2);
+#endif // VERILATOR
 
   // init remote-bitbang
   if (enable_simjtag) {
@@ -434,8 +440,14 @@ Emulator::Emulator(int argc, const char *argv[])
 #endif
 
   // set log time range and log level
+#ifdef VERILATOR
   dut_ptr->difftest_logCtrl_begin = args.log_begin;
   dut_ptr->difftest_logCtrl_end = args.log_end;
+#endif // VERILATOR
+#ifdef GSIM
+  dut_ptr->set_difftest$$logCtrl$$begin(args.log_begin);
+  dut_ptr->set_difftest$$logCtrl$$end(args.log_end);
+#endif // GSIM
 
 #ifndef CONFIG_NO_DIFFTEST
   // init difftest
@@ -580,6 +592,7 @@ inline void Emulator::reset_ncycles(size_t cycles) {
     return;
   }
   for (int i = 0; i < cycles; i++) {
+#ifdef VERILATOR
     dut_ptr->reset = 1;
 #ifdef COVERAGE_PORT_RESET
     dut_ptr->coverage_reset = dut_ptr->reset;
@@ -612,6 +625,14 @@ inline void Emulator::reset_ncycles(size_t cycles) {
 #ifdef COVERAGE_PORT_RESET
     dut_ptr->coverage_reset = dut_ptr->reset;
 #endif // COVERAGE_PORT_RESET
+#endif // VERILATOR
+
+#ifdef GSIM
+    dut_ptr->set_reset(1);
+    dut_ptr->step();
+    dut_ptr->set_reset(0);
+    dut_ptr->step();
+#endif // GSIM
   }
 }
 
@@ -620,11 +641,13 @@ inline void Emulator::single_cycle() {
     goto end_single_cycle;
   }
 
+#ifdef VERILATOR
   dut_ptr->clock = 1;
 #ifdef COVERAGE_PORT_CLOCK
   dut_ptr->coverage_clock = dut_ptr->clock;
 #endif // COVERAGE_PORT_CLOCK
   dut_ptr->eval();
+#endif // VERILATOR
 
 #if VM_TRACE == 1
   if (args.enable_waveform) {
@@ -649,6 +672,7 @@ inline void Emulator::single_cycle() {
   dramsim3_step();
 #endif
 
+#ifdef VERILATOR
   if (dut_ptr->difftest_uart_out_valid) {
     printf("%c", dut_ptr->difftest_uart_out_ch);
     fflush(stdout);
@@ -663,6 +687,20 @@ inline void Emulator::single_cycle() {
   dut_ptr->coverage_clock = dut_ptr->clock;
 #endif // COVERAGE_PORT_CLOCK
   dut_ptr->eval();
+#endif // VERILATOR
+
+#ifdef GSIM
+  dut_ptr->step();
+  if (dut_ptr->get_difftest$$uart$$out$$valid()) {
+    printf("%c", dut_ptr->get_difftest$$uart$$out$$ch());
+    fflush(stdout);
+  }
+  if (dut_ptr->get_difftest$$uart$$in$$valid()) {
+    extern uint8_t uart_getc();
+    uint8_t ch = uart_getc();
+    dut_ptr->set_difftest$$uart$$in$$ch(ch);
+  }
+#endif // GSIM
 
 #if VM_TRACE == 1
   if (args.enable_waveform && args.enable_waveform_full) {
@@ -749,11 +787,17 @@ int Emulator::tick() {
   }
 
   // exit signal: non-zero exit exits the simulation. exit all 1's indicates good.
-  if (dut_ptr->difftest_exit) {
-    if (dut_ptr->difftest_exit == -1UL) {
+#ifdef VERILATOR
+  uint64_t difftest_exit = dut_ptr->difftest_exit;
+#endif
+#ifdef GSIM
+  uint64_t difftest_exit = 0; // TODO: gsim API
+#endif
+  if (difftest_exit) {
+    if (difftest_exit == -1UL) {
       trapCode = STATE_SIM_EXIT;
     } else {
-      Info("The simulation aborted via the top-level exit of 0x%lx.\n", dut_ptr->difftest_exit);
+      Info("The simulation aborted via the top-level exit of 0x%lx.\n", difftest_exit);
       trapCode = STATE_ABORT;
     }
   }
@@ -766,13 +810,25 @@ int Emulator::tick() {
     auto trap = difftest[i]->get_trap_event();
     if (trap->instrCnt >= args.warmup_instr) {
       Info("Warmup finished. The performance counters will be dumped and then reset.\n");
+#ifdef VERILATOR
       dut_ptr->difftest_perfCtrl_clean = 1;
       dut_ptr->difftest_perfCtrl_dump = 1;
+#endif // VERILATOR
+#ifdef GSIM
+      dut_ptr->set_difftest$$perfCtrl$$clean(1);
+      dut_ptr->set_difftest$$perfCtrl$$dump(1);
+#endif // GSIM
       args.warmup_instr = -1;
     }
     if (trap->cycleCnt % args.stat_cycles == args.stat_cycles - 1) {
+#ifdef VERILATOR
       dut_ptr->difftest_perfCtrl_clean = 1;
       dut_ptr->difftest_perfCtrl_dump = 1;
+#endif // VERILATOR
+#ifdef GSIM
+      dut_ptr->set_difftest$$perfCtrl$$clean(1);
+      dut_ptr->set_difftest$$perfCtrl$$dump(1);
+#endif // GSIM
     }
 #ifdef ENABLE_IPC
     if (trap->instrCnt >= args.ipc_times * args.ipc_interval &&
@@ -807,16 +863,26 @@ int Emulator::tick() {
 #ifdef CONFIG_NO_DIFFTEST
   args.max_cycles--;
 #endif // CONFIG_NO_DIFFTEST
+#ifdef VERILATOR
   dut_ptr->difftest_perfCtrl_clean = 0;
   dut_ptr->difftest_perfCtrl_dump = 0;
-
+#endif // VERILATOR
+#ifdef GSIM
+  dut_ptr->set_difftest$$perfCtrl$$clean(0);
+  dut_ptr->set_difftest$$perfCtrl$$dump(0);
+#endif // GSIM
 #ifndef CONFIG_NO_DIFFTEST
   int step = 0;
   if (args.trace_name && args.trace_is_read) {
     step = 1;
     difftest_trace_read();
   } else {
+#ifdef VERILATOR
     step = dut_ptr->difftest_step;
+#endif // VERILATOR
+#ifdef GSIM
+    step = 1; // TODO: gsim API
+#endif        // GSIM
   }
 
   static uint64_t stuck_timer = 0;
@@ -906,7 +972,11 @@ int Emulator::tick() {
 }
 
 int Emulator::is_finished() {
-  return Verilated::gotFinish() || trapCode != STATE_RUNNING;
+  return
+#ifdef VERILATOR
+      Verilated::gotFinish() ||
+#endif // VERILATOR
+      trapCode != STATE_RUNNING;
 }
 
 int Emulator::is_good() {
@@ -992,10 +1062,18 @@ inline void Emulator::save_coverage(time_t t) {
 #endif
 
 void Emulator::trigger_stat_dump() {
+#ifdef VERILATOR
   dut_ptr->difftest_perfCtrl_dump = 1;
   if (get_args().force_dump_result) {
     dut_ptr->difftest_logCtrl_end = -1;
   }
+#endif // VERILATOR
+#ifdef GSIM
+  dut_ptr->set_difftest$$perfCtrl$$dump(1);
+  if (get_args().force_dump_result) {
+    dut_ptr->set_difftest$$logCtrl$$end(-1);
+  }
+#endif // GSIM
   single_cycle();
 }
 
diff --git a/src/test/csrc/verilator/emu.h b/src/test/csrc/verilator/emu.h
index 59563be47..b39b64a4f 100644
--- a/src/test/csrc/verilator/emu.h
+++ b/src/test/csrc/verilator/emu.h
@@ -17,24 +17,30 @@
 #ifndef __EMU_H
 #define __EMU_H
 
+#ifdef VERILATOR
 #include "VSimTop.h"
 #include "VSimTop__Syms.h"
+#define DUT_TOP VSimTop
+#endif // VERILATOR
+#ifdef GSIM
+#include "SimTop.h"
+#define DUT_TOP SSimTop
+#endif
 #include "common.h"
 #include "dut.h"
 #include "lightsss.h"
 #include "snapshot.h"
 #include <sys/types.h>
-#ifdef ENABLE_FST
-#include <verilated_fst_c.h>
-#else
-#include <verilated_vcd_c.h> // Trace file format header
-#endif
 #ifdef EMU_THREAD
 #include <verilated_threads.h>
 #endif
 #if VM_TRACE == 1
-#include <verilated_vcd_c.h> // Trace file format header
-#endif
+#ifdef ENABLE_FST
+#include <verilated_fst_c.h>
+#else
+#include <verilated_vcd_c.h>
+#endif // ENABLE_FST
+#endif // VM_TRACE
 
 struct EmuArgs {
   uint32_t reset_cycles = 50;
@@ -85,12 +91,14 @@ struct EmuArgs {
 
 class Emulator final : public DUT {
 private:
-  VSimTop *dut_ptr;
+  DUT_TOP *dut_ptr;
+#if VM_TRACE == 1
 #ifdef ENABLE_FST
   VerilatedFstC *tfp;
 #else
   VerilatedVcdC *tfp;
 #endif
+#endif // VM_TRACE == 1
   bool force_dump_wave = false;
 #ifdef VM_SAVABLE
   VerilatedSaveMem *snapshot_slot = nullptr;