diff --git a/lib/CPUs/JCpu/ghdl/cpu_embedded.make b/lib/CPUs/JCpu/ghdl/cpu_embedded.make
index 42660ca..cbb3876 100644
--- a/lib/CPUs/JCpu/ghdl/cpu_embedded.make
+++ b/lib/CPUs/JCpu/ghdl/cpu_embedded.make
@@ -11,7 +11,6 @@ SRCS += ../src/tb_cpu_embedded.vhd
 # Compile
 TARGET := cpu_embedded
 ENTITY := tb_cpu_embedded
-WITH_GHW := y
 
 include $(VHDL_HOME)/make/ghdl.mk
 
diff --git a/lib/CPUs/JCpu/ghdl/cpu_itest.make b/lib/CPUs/JCpu/ghdl/cpu_itest.make
index 156aff6..e7de19c 100644
--- a/lib/CPUs/JCpu/ghdl/cpu_itest.make
+++ b/lib/CPUs/JCpu/ghdl/cpu_itest.make
@@ -12,7 +12,6 @@ SRCS += ../src/tb_cpu_itest.vhd
 # Compile
 TARGET := cpu_itest
 ENTITY := tb_cpu
-WITH_GHW := y
 
 include $(VHDL_HOME)/make/ghdl.mk
 
diff --git a/lib/CPUs/JCpu/ghdl/mul8x8.make b/lib/CPUs/JCpu/ghdl/mul8x8.make
index 4c3949c..b211dd7 100644
--- a/lib/CPUs/JCpu/ghdl/mul8x8.make
+++ b/lib/CPUs/JCpu/ghdl/mul8x8.make
@@ -11,7 +11,6 @@ SRCS += ../src/tb_cpu_embedded.vhd
 # Compile
 TARGET := mul8x8
 ENTITY := tb_cpu_embedded
-WITH_GHW := y
 
 include $(VHDL_HOME)/make/ghdl.mk
 
diff --git a/lib/CPUs/JCpu/ghdl/reti_issue.make b/lib/CPUs/JCpu/ghdl/reti_issue.make
index 1625e5a..fb3d3c0 100644
--- a/lib/CPUs/JCpu/ghdl/reti_issue.make
+++ b/lib/CPUs/JCpu/ghdl/reti_issue.make
@@ -12,7 +12,6 @@ SRCS += ../src/tb_cpu_itest.vhd
 # Compile
 TARGET := reti_issue
 ENTITY := tb_cpu
-WITH_GHW := y
 
 include $(VHDL_HOME)/make/ghdl.mk
 
diff --git a/make/ghdl.mk b/make/ghdl.mk
index 03ab894..caf9b4e 100644
--- a/make/ghdl.mk
+++ b/make/ghdl.mk
@@ -10,6 +10,7 @@ WORK_LIB ?= work
 LANG_STD ?= 93c
 IEEE_STD ?= standard
 RUN_TIME ?= 1000ns
+WAVE_FORMAT ?= FST
 
 # Build path
 BUILD_DIR ?= build/$(TARGET)
@@ -40,20 +41,23 @@ SRCS := $(filter-out  ,$(SRCS))
 GHDL := ghdl
 GHDL_GCC := ghdl-gcc
 
-# Output stuff
-SIM_FILE-$(WITH_VCD) := $(BUILD_DIR)/$(TARGET).vcd
-SIM_FILE-$(WITH_FST) := $(BUILD_DIR)/$(TARGET).fst
-SIM_FILE-$(WITH_GHW) := $(BUILD_DIR)/$(TARGET).ghw
+# Wave format selection
+SIM_FILE-VCD := $(BUILD_DIR)/$(TARGET).vcd
+GTK_OPTS-VCD := --vcd=$(SIM_FILE-VCD)
 
-GTK_OPTS-$(WITH_VCD) := --vcd=$(SIM_FILE-y)
-GTK_OPTS-$(WITH_FST) := --fst=$(SIM_FILE-y)
-GTK_OPTS-$(WITH_GHW) := --wave=$(SIM_FILE-y)
+SIM_FILE-FST := $(BUILD_DIR)/$(TARGET).fst
+GTK_OPTS-FST := --fst=$(SIM_FILE-FST)
+
+SIM_FILE-GHW := $(BUILD_DIR)/$(TARGET).ghw
+GTK_OPTS-GHW := --wave=$(SIM_FILE-GHW)
+
+SIM_FILE := $(SIM_FILE-$(WAVE_FORMAT))
+GTK_OPTS := $(GTK_OPTS-$(WAVE_FORMAT))
 
 # -------------------------------------------------
 # Targets
 # -------------------------------------------------
 
-
 all:  analyze
 
 $(WORK_DIR):
@@ -86,16 +90,16 @@ run: analyze
 	$(GHDL) -r $(GHDL_OPTS) $(ENTITY) $(RUN_OPTS)
 	
 run_wave: analyze
-	$(GHDL) -r $(GHDL_OPTS) $(ENTITY) $(RUN_OPTS) $(GTK_OPTS-y) >$(BUILD_DIR)/$(TARGET).log
+	$(GHDL) -r $(GHDL_OPTS) $(ENTITY) $(RUN_OPTS) $(GTK_OPTS) >$(BUILD_DIR)/$(TARGET).log
 
 synth: analyze
 	$(GHDL) --synth $(GHDL_OPTS) $(ENTITY)
 
 wave: run_wave
-	exec gtkwave -f $(SIM_FILE-y) -a $(BUILD_DIR)/$(TARGET).gtkw &
+	exec gtkwave -f $(SIM_FILE) -a $(BUILD_DIR)/$(TARGET).gtkw &
 	
 result:
-	exec gtkwave -f $(SIM_FILE-y) -a $(BUILD_DIR)/$(TARGET).gtkw &
+	exec gtkwave -f $(SIM_FILE) -a $(BUILD_DIR)/$(TARGET).gtkw &
 
 tree: analyze
 	$(GHDL) -r $(GHDL_OPTS) $(ENTITY) $(RUN_OPTS) --no-run --disp-tree=inst