fix: add custom testbench

Author: ezelioli

test/Makefile

@@ -170,11 +170,12 @@ vsim-clean:
 ########## Verilator #############
 ##################################
 
+VERILATOR_JOBS      ?= 0
 VERILATOR_BUILD_DIR := $(VERILATOR_DIR)/build
 VERILATOR_LOG_DIR   := $(VERILATOR_DIR)/logs
 VERILATOR_FLIST     := $(VERILATOR_DIR)/cva6tb.flist
 VERILATOR_WARNINGS  := -Wall -Wno-fatal -Wno-style -Wno-BLKANDNBLK -Wno-WIDTHEXPAND -Wno-WIDTHTRUNC -Wno-WIDTHCONCAT -Wno-ASCRANGE -Wno-IMPLICITSTATIC
-VERILATOR_FLAGS     := --binary -j 0 --Mdir $(VERILATOR_BUILD_DIR) $(VERILATOR_WARNINGS) -O3 -f $(VERILATOR_FLIST) --assert --timing \
+VERILATOR_FLAGS     := --binary -j $(VERILATOR_JOBS) --Mdir $(VERILATOR_BUILD_DIR) $(VERILATOR_WARNINGS) -O3 -f $(VERILATOR_FLIST) --assert --timing \
 	--trace-fst --trace-structs --trace-threads 2 --x-assign fast --x-initial fast
 
 $(VERILATOR_LOG_DIR):