diff --git a/Makefile b/Makefile
index 60583cbad..2f54eb046 100644
--- a/Makefile
+++ b/Makefile
@@ -80,7 +80,7 @@ list_incdir := $(foreach dir, ${incdir}, +incdir+$(dir))
 
 # Build the TB and module using QuestaSim
 build: $(library) $(library)/.build-agents $(library)/.build-interfaces $(library)/.build-components \
-		$(library)/.build-srcs $(library)/.build-tb
+		$(library)/.build-srcs $(library)/.build-tb $(library)/.build-dpi
 		# Optimize top level
 	vopt$(questa_version) $(compile_flag) -work $(library)  $(test_top_level) -o $(test_top_level)_optimized +acc -check_synthesis
 
@@ -93,11 +93,17 @@ $(library)/.build-srcs: $(util) $(src)
 	touch $(library)/.build-srcs
 
 # build TBs
-$(library)/.build-tb: $(dpi) $(tbs)
-	# Compile top level with DPI headers
-	vlog$(questa_version) -sv $(tbs) -work $(library) $(filter %.c %.cc, $(dpi)) -ccflags "-g -std=c++11 " -dpiheader tb/dpi/elfdpi.h
+$(library)/.build-tb: $(tbs)
+	# Compile top level
+	vlog$(questa_version) -sv $(tbs) -work $(library)
 	touch $(library)/.build-tb
 
+# compile DPIs
+$(library)/.build-dpi: $(dpi)
+	# Compile C-code and generate .so file
+	g++ -c -fPIC -m64 -std=c++0x -I$(QUESTASIM_HOME)/include -shared -o $(library)/elf_dpi.o -c $(filter %.c %.cc, $(dpi))
+	g++ -shared -m64 -o $(library)/elf_dpi.so $(library)/elf_dpi.o
+	touch $(library)/.build-dpi
 
 # Compile Sequences and Tests
 $(library)/.build-components: $(envs) $(sequences) $(test_pkg)
@@ -120,22 +126,22 @@ $(library):
 	vlib${questa_version} ${library}
 
 sim: build
-	vsim${questa_version} -lib ${library} ${top_level}_optimized +UVM_TESTNAME=${test_case} +BASEDIR=$(riscv-test-dir) \
-	+ASMTEST=$(riscv-test)  $(uvm-flags) +UVM_VERBOSITY=HIGH -coverage -classdebug -do "do tb/wave/wave_core.do"
+	vsim${questa_version} -64 -lib ${library} ${top_level}_optimized +UVM_TESTNAME=${test_case} +BASEDIR=$(riscv-test-dir) \
+	+ASMTEST=$(riscv-test)  $(uvm-flags) +UVM_VERBOSITY=HIGH -coverage -classdebug -sv_lib $(library)/elf_dpi -do "do tb/wave/wave_core.do"
 
 sim_nopt: build
-	vsim${questa_version} -novopt -lib ${library} ${top_level} +UVM_TESTNAME=${test_case} +BASEDIR=$(riscv-test-dir) \
-	+ASMTEST=$(riscv-test)  $(uvm-flags) +UVM_VERBOSITY=HIGH -coverage -classdebug -do "do tb/wave/wave_core.do"
+	vsim${questa_version} -64 -novopt -lib ${library} ${top_level} +UVM_TESTNAME=${test_case} +BASEDIR=$(riscv-test-dir) \
+	+ASMTEST=$(riscv-test)  $(uvm-flags) +UVM_VERBOSITY=HIGH -coverage -classdebug -sv_lib $(library)/elf_dpi -do "do tb/wave/wave_core.do"
 
 
 simc: build
-	vsim${questa_version} -c -lib ${library} ${top_level}_optimized +max-cycles=$(max_cycles) +UVM_TESTNAME=${test_case} \
-	 +BASEDIR=$(riscv-test-dir) $(uvm-flags) +ASMTEST=$(riscv-test) -coverage -classdebug -do "do tb/wave/wave_core.do"
+	vsim${questa_version} -64 -c -lib ${library} ${top_level}_optimized +max-cycles=$(max_cycles) +UVM_TESTNAME=${test_case} \
+	 +BASEDIR=$(riscv-test-dir) $(uvm-flags) +ASMTEST=$(riscv-test) "+UVM_VERBOSITY=HIGH" -coverage -classdebug -sv_lib $(library)/elf_dpi -do "do tb/wave/wave_core.do"
 
 run-asm-tests: build
-	$(foreach test, $(riscv-tests), vsim$(questa_version) +BASEDIR=$(riscv-test-dir) +max-cycles=$(max_cycles) \
+	$(foreach test, $(riscv-tests), vsim$(questa_version) -64 +BASEDIR=$(riscv-test-dir) +max-cycles=$(max_cycles) \
 		+UVM_TESTNAME=$(test_case) $(uvm-flags) +ASMTEST=$(test) +uvm_set_action="*,_ALL_,UVM_ERROR,UVM_DISPLAY|UVM_STOP" -c \
-		-coverage -classdebug -do "coverage save -onexit $@.ucdb; run -a; quit -code [coverage attribute -name TESTSTATUS -concise]"  \
+		-coverage -classdebug  -sv_lib $(library)/elf_dpi -do "coverage save -onexit $@.ucdb; run -a; quit -code [coverage attribute -name TESTSTATUS -concise]"  \
 		$(library).$(test_top_level)_optimized;)
 
 run-asm-tests-verilator: verilate
@@ -145,9 +151,9 @@ run-failed-tests: build
 	# make the tests
 	cd failedtests && make
 	# run the RTL simulation
-	$(foreach test, $(failed-tests:.S=), vsim$(questa_version) +BASEDIR=. +max-cycles=$(max_cycles) \
+	$(foreach test, $(failed-tests:.S=), vsim$(questa_version) -64 +BASEDIR=. +max-cycles=$(max_cycles) \
 		+UVM_TESTNAME=$(test_case)  $(uvm-flags) +ASMTEST=$(test) +signature=$(test).rtlsim.sig +uvm_set_action="*,_ALL_,UVM_ERROR,UVM_DISPLAY|UVM_STOP" -c \
-		-coverage -classdebug -do "coverage save -onexit $@.ucdb; run -a; quit -code [coverage attribute -name TESTSTATUS -concise]" \
+		-coverage -classdebug  -sv_lib $(library)/elf_dpi -do "coverage save -onexit $@.ucdb; run -a; quit -code [coverage attribute -name TESTSTATUS -concise]" \
 		$(library).$(test_top_level)_optimized;)
 	# run it on spike
 	$(foreach test, $(failed-tests:.S=), spike +signature=$(test).spike.sig $(test);)
@@ -160,8 +166,8 @@ $(tests): build
 	vopt${questa_version} -work ${library} ${compile_flag} $@_tb -o $@_tb_optimized +acc -check_synthesis
 	# vsim${questa_version} $@_tb_optimized
 	# vsim${questa_version} +UVM_TESTNAME=$@_test -coverage -classdebug $@_tb_optimized
-	vsim${questa_version} +UVM_TESTNAME=$@_test +ASMTEST=$(riscv-test-dir)/$(riscv-test) \
-	+uvm_set_action="*,_ALL_,UVM_ERROR,UVM_DISPLAY|UVM_STOP" -c -coverage -classdebug \
+	vsim${questa_version} -64 +UVM_TESTNAME=$@_test +ASMTEST=$(riscv-test-dir)/$(riscv-test) \
+	+uvm_set_action="*,_ALL_,UVM_ERROR,UVM_DISPLAY|UVM_STOP" -c -coverage -classdebug -sv_lib $(library)/elf_dpi \
 	-do "coverage save -onexit $@.ucdb; run -a; quit -code [coverage attribute -name TESTSTATUS -concise]" \
 	${library}.$@_tb_optimized