diff --git a/tests/gmii/Makefile b/tests/gmii/Makefile
index a7b00b3..4e58f31 100644
--- a/tests/gmii/Makefile
+++ b/tests/gmii/Makefile
@@ -31,8 +31,6 @@ TOPLEVEL = $(DUT)
 MODULE   = $(DUT)
 VERILOG_SOURCES += $(DUT).v
 
-SIM_BUILD ?= sim_build_$(MODULE)
-
 ifeq ($(SIM), icarus)
 	PLUSARGS += -fst
 
@@ -48,6 +46,8 @@ else ifeq ($(SIM), verilator)
 	endif
 endif
 
+include $(shell cocotb-config --makefiles)/Makefile.sim
+
 iverilog_dump.v:
 	echo 'module iverilog_dump();' > $@
 	echo 'initial begin' >> $@
@@ -57,9 +57,5 @@ iverilog_dump.v:
 	echo 'endmodule' >> $@
 
 clean::
-	@rm -rf sim_build_*
 	@rm -rf iverilog_dump.v
 	@rm -rf dump.fst $(TOPLEVEL).fst
-
-include $(shell cocotb-config --makefiles)/Makefile.sim
-
diff --git a/tests/gmii/test_gmii.py b/tests/gmii/test_gmii.py
index f9a2ed7..735b1a4 100644
--- a/tests/gmii/test_gmii.py
+++ b/tests/gmii/test_gmii.py
@@ -160,8 +160,8 @@ def test_gmii(request):
 
     extra_env = {f'PARAM_{k}': str(v) for k, v in parameters.items()}
 
-    sim_build = os.path.join(tests_dir,
-        "sim_build_"+request.node.name.replace('[', '-').replace(']', ''))
+    sim_build = os.path.join(tests_dir, "sim_build",
+        request.node.name.replace('[', '-').replace(']', ''))
 
     cocotb_test.simulator.run(
         python_search=[tests_dir],
diff --git a/tests/gmii_phy/Makefile b/tests/gmii_phy/Makefile
index 241db7d..8df36c0 100644
--- a/tests/gmii_phy/Makefile
+++ b/tests/gmii_phy/Makefile
@@ -31,8 +31,6 @@ TOPLEVEL = $(DUT)
 MODULE   = $(DUT)
 VERILOG_SOURCES += $(DUT).v
 
-SIM_BUILD ?= sim_build_$(MODULE)
-
 ifeq ($(SIM), icarus)
 	PLUSARGS += -fst
 
@@ -48,6 +46,8 @@ else ifeq ($(SIM), verilator)
 	endif
 endif
 
+include $(shell cocotb-config --makefiles)/Makefile.sim
+
 iverilog_dump.v:
 	echo 'module iverilog_dump();' > $@
 	echo 'initial begin' >> $@
@@ -57,9 +57,5 @@ iverilog_dump.v:
 	echo 'endmodule' >> $@
 
 clean::
-	@rm -rf sim_build_*
 	@rm -rf iverilog_dump.v
 	@rm -rf dump.fst $(TOPLEVEL).fst
-
-include $(shell cocotb-config --makefiles)/Makefile.sim
-
diff --git a/tests/gmii_phy/test_gmii_phy.py b/tests/gmii_phy/test_gmii_phy.py
index 6403a9f..73e5141 100644
--- a/tests/gmii_phy/test_gmii_phy.py
+++ b/tests/gmii_phy/test_gmii_phy.py
@@ -170,8 +170,8 @@ def test_gmii_phy(request):
 
     extra_env = {f'PARAM_{k}': str(v) for k, v in parameters.items()}
 
-    sim_build = os.path.join(tests_dir,
-        "sim_build_"+request.node.name.replace('[', '-').replace(']', ''))
+    sim_build = os.path.join(tests_dir, "sim_build",
+        request.node.name.replace('[', '-').replace(']', ''))
 
     cocotb_test.simulator.run(
         python_search=[tests_dir],
diff --git a/tests/mii/Makefile b/tests/mii/Makefile
index 4658172..00cac64 100644
--- a/tests/mii/Makefile
+++ b/tests/mii/Makefile
@@ -31,8 +31,6 @@ TOPLEVEL = $(DUT)
 MODULE   = $(DUT)
 VERILOG_SOURCES += $(DUT).v
 
-SIM_BUILD ?= sim_build_$(MODULE)
-
 ifeq ($(SIM), icarus)
 	PLUSARGS += -fst
 
@@ -48,6 +46,8 @@ else ifeq ($(SIM), verilator)
 	endif
 endif
 
+include $(shell cocotb-config --makefiles)/Makefile.sim
+
 iverilog_dump.v:
 	echo 'module iverilog_dump();' > $@
 	echo 'initial begin' >> $@
@@ -57,9 +57,5 @@ iverilog_dump.v:
 	echo 'endmodule' >> $@
 
 clean::
-	@rm -rf sim_build_*
 	@rm -rf iverilog_dump.v
 	@rm -rf dump.fst $(TOPLEVEL).fst
-
-include $(shell cocotb-config --makefiles)/Makefile.sim
-
diff --git a/tests/mii/test_mii.py b/tests/mii/test_mii.py
index 1cf617c..7a9e668 100644
--- a/tests/mii/test_mii.py
+++ b/tests/mii/test_mii.py
@@ -157,8 +157,8 @@ def test_mii(request):
 
     extra_env = {f'PARAM_{k}': str(v) for k, v in parameters.items()}
 
-    sim_build = os.path.join(tests_dir,
-        "sim_build_"+request.node.name.replace('[', '-').replace(']', ''))
+    sim_build = os.path.join(tests_dir, "sim_build",
+        request.node.name.replace('[', '-').replace(']', ''))
 
     cocotb_test.simulator.run(
         python_search=[tests_dir],
diff --git a/tests/mii_phy/Makefile b/tests/mii_phy/Makefile
index 4200585..063d360 100644
--- a/tests/mii_phy/Makefile
+++ b/tests/mii_phy/Makefile
@@ -31,8 +31,6 @@ TOPLEVEL = $(DUT)
 MODULE   = $(DUT)
 VERILOG_SOURCES += $(DUT).v
 
-SIM_BUILD ?= sim_build_$(MODULE)
-
 ifeq ($(SIM), icarus)
 	PLUSARGS += -fst
 
@@ -48,6 +46,8 @@ else ifeq ($(SIM), verilator)
 	endif
 endif
 
+include $(shell cocotb-config --makefiles)/Makefile.sim
+
 iverilog_dump.v:
 	echo 'module iverilog_dump();' > $@
 	echo 'initial begin' >> $@
@@ -57,9 +57,5 @@ iverilog_dump.v:
 	echo 'endmodule' >> $@
 
 clean::
-	@rm -rf sim_build_*
 	@rm -rf iverilog_dump.v
 	@rm -rf dump.fst $(TOPLEVEL).fst
-
-include $(shell cocotb-config --makefiles)/Makefile.sim
-
diff --git a/tests/mii_phy/test_mii_phy.py b/tests/mii_phy/test_mii_phy.py
index 00e868b..8a725d6 100644
--- a/tests/mii_phy/test_mii_phy.py
+++ b/tests/mii_phy/test_mii_phy.py
@@ -161,8 +161,8 @@ def test_mii_phy(request):
 
     extra_env = {f'PARAM_{k}': str(v) for k, v in parameters.items()}
 
-    sim_build = os.path.join(tests_dir,
-        "sim_build_"+request.node.name.replace('[', '-').replace(']', ''))
+    sim_build = os.path.join(tests_dir, "sim_build",
+        request.node.name.replace('[', '-').replace(']', ''))
 
     cocotb_test.simulator.run(
         python_search=[tests_dir],
diff --git a/tests/ptp_clock/Makefile b/tests/ptp_clock/Makefile
index 191c4d2..9ed43ec 100644
--- a/tests/ptp_clock/Makefile
+++ b/tests/ptp_clock/Makefile
@@ -31,8 +31,6 @@ TOPLEVEL = $(DUT)
 MODULE   = $(DUT)
 VERILOG_SOURCES += $(DUT).v
 
-SIM_BUILD ?= sim_build_$(MODULE)
-
 ifeq ($(SIM), icarus)
 	PLUSARGS += -fst
 
@@ -48,6 +46,8 @@ else ifeq ($(SIM), verilator)
 	endif
 endif
 
+include $(shell cocotb-config --makefiles)/Makefile.sim
+
 iverilog_dump.v:
 	echo 'module iverilog_dump();' > $@
 	echo 'initial begin' >> $@
@@ -57,9 +57,5 @@ iverilog_dump.v:
 	echo 'endmodule' >> $@
 
 clean::
-	@rm -rf sim_build_*
 	@rm -rf iverilog_dump.v
 	@rm -rf dump.fst $(TOPLEVEL).fst
-
-include $(shell cocotb-config --makefiles)/Makefile.sim
-
diff --git a/tests/ptp_clock/test_ptp_clock.py b/tests/ptp_clock/test_ptp_clock.py
index 19bedd0..7cf5e03 100644
--- a/tests/ptp_clock/test_ptp_clock.py
+++ b/tests/ptp_clock/test_ptp_clock.py
@@ -310,8 +310,8 @@ def test_ptp_clock(request):
 
     extra_env = {f'PARAM_{k}': str(v) for k, v in parameters.items()}
 
-    sim_build = os.path.join(tests_dir,
-        "sim_build_"+request.node.name.replace('[', '-').replace(']', ''))
+    sim_build = os.path.join(tests_dir, "sim_build",
+        request.node.name.replace('[', '-').replace(']', ''))
 
     cocotb_test.simulator.run(
         python_search=[tests_dir],
diff --git a/tests/rgmii/Makefile b/tests/rgmii/Makefile
index f44dd8b..20e1e51 100644
--- a/tests/rgmii/Makefile
+++ b/tests/rgmii/Makefile
@@ -31,8 +31,6 @@ TOPLEVEL = $(DUT)
 MODULE   = $(DUT)
 VERILOG_SOURCES += $(DUT).v
 
-SIM_BUILD ?= sim_build_$(MODULE)
-
 ifeq ($(SIM), icarus)
 	PLUSARGS += -fst
 
@@ -48,6 +46,8 @@ else ifeq ($(SIM), verilator)
 	endif
 endif
 
+include $(shell cocotb-config --makefiles)/Makefile.sim
+
 iverilog_dump.v:
 	echo 'module iverilog_dump();' > $@
 	echo 'initial begin' >> $@
@@ -57,9 +57,5 @@ iverilog_dump.v:
 	echo 'endmodule' >> $@
 
 clean::
-	@rm -rf sim_build_*
 	@rm -rf iverilog_dump.v
 	@rm -rf dump.fst $(TOPLEVEL).fst
-
-include $(shell cocotb-config --makefiles)/Makefile.sim
-
diff --git a/tests/rgmii/test_rgmii.py b/tests/rgmii/test_rgmii.py
index 6dadd8c..c6547c0 100644
--- a/tests/rgmii/test_rgmii.py
+++ b/tests/rgmii/test_rgmii.py
@@ -157,8 +157,8 @@ def test_rgmii(request):
 
     extra_env = {f'PARAM_{k}': str(v) for k, v in parameters.items()}
 
-    sim_build = os.path.join(tests_dir,
-        "sim_build_"+request.node.name.replace('[', '-').replace(']', ''))
+    sim_build = os.path.join(tests_dir, "sim_build",
+        request.node.name.replace('[', '-').replace(']', ''))
 
     cocotb_test.simulator.run(
         python_search=[tests_dir],
diff --git a/tests/rgmii_phy/Makefile b/tests/rgmii_phy/Makefile
index 5619100..0e61ca4 100644
--- a/tests/rgmii_phy/Makefile
+++ b/tests/rgmii_phy/Makefile
@@ -31,8 +31,6 @@ TOPLEVEL = $(DUT)
 MODULE   = $(DUT)
 VERILOG_SOURCES += $(DUT).v
 
-SIM_BUILD ?= sim_build_$(MODULE)
-
 ifeq ($(SIM), icarus)
 	PLUSARGS += -fst
 
@@ -48,6 +46,8 @@ else ifeq ($(SIM), verilator)
 	endif
 endif
 
+include $(shell cocotb-config --makefiles)/Makefile.sim
+
 iverilog_dump.v:
 	echo 'module iverilog_dump();' > $@
 	echo 'initial begin' >> $@
@@ -57,9 +57,5 @@ iverilog_dump.v:
 	echo 'endmodule' >> $@
 
 clean::
-	@rm -rf sim_build_*
 	@rm -rf iverilog_dump.v
 	@rm -rf dump.fst $(TOPLEVEL).fst
-
-include $(shell cocotb-config --makefiles)/Makefile.sim
-
diff --git a/tests/rgmii_phy/test_rgmii_phy.py b/tests/rgmii_phy/test_rgmii_phy.py
index ece35fb..7b477f2 100644
--- a/tests/rgmii_phy/test_rgmii_phy.py
+++ b/tests/rgmii_phy/test_rgmii_phy.py
@@ -174,8 +174,8 @@ def test_rgmii_phy(request):
 
     extra_env = {f'PARAM_{k}': str(v) for k, v in parameters.items()}
 
-    sim_build = os.path.join(tests_dir,
-        "sim_build_"+request.node.name.replace('[', '-').replace(']', ''))
+    sim_build = os.path.join(tests_dir, "sim_build",
+        request.node.name.replace('[', '-').replace(']', ''))
 
     cocotb_test.simulator.run(
         python_search=[tests_dir],
diff --git a/tests/xgmii/Makefile b/tests/xgmii/Makefile
index e46fb3c..1b6f4a4 100644
--- a/tests/xgmii/Makefile
+++ b/tests/xgmii/Makefile
@@ -35,8 +35,6 @@ VERILOG_SOURCES += $(DUT).v
 export PARAM_DATA_WIDTH ?= 64
 export PARAM_CTRL_WIDTH ?= $(shell expr $(PARAM_DATA_WIDTH) / 8 )
 
-SIM_BUILD ?= sim_build_$(MODULE)-$(PARAM_DATA_WIDTH)
-
 ifeq ($(SIM), icarus)
 	PLUSARGS += -fst
 
@@ -58,6 +56,8 @@ else ifeq ($(SIM), verilator)
 	endif
 endif
 
+include $(shell cocotb-config --makefiles)/Makefile.sim
+
 iverilog_dump.v:
 	echo 'module iverilog_dump();' > $@
 	echo 'initial begin' >> $@
@@ -67,9 +67,5 @@ iverilog_dump.v:
 	echo 'endmodule' >> $@
 
 clean::
-	@rm -rf sim_build_*
 	@rm -rf iverilog_dump.v
 	@rm -rf dump.fst $(TOPLEVEL).fst
-
-include $(shell cocotb-config --makefiles)/Makefile.sim
-
diff --git a/tests/xgmii/test_xgmii.py b/tests/xgmii/test_xgmii.py
index 3692897..43c33de 100644
--- a/tests/xgmii/test_xgmii.py
+++ b/tests/xgmii/test_xgmii.py
@@ -249,8 +249,8 @@ def test_xgmii(request, data_width):
 
     extra_env = {f'PARAM_{k}': str(v) for k, v in parameters.items()}
 
-    sim_build = os.path.join(tests_dir,
-        "sim_build_"+request.node.name.replace('[', '-').replace(']', ''))
+    sim_build = os.path.join(tests_dir, "sim_build",
+        request.node.name.replace('[', '-').replace(']', ''))
 
     cocotb_test.simulator.run(
         python_search=[tests_dir],