diff --git a/Makefile b/Makefile
index aa95ffa..57e7aba 100644
--- a/Makefile
+++ b/Makefile
@@ -1,11 +1,18 @@
+###########################################################################
 ## Xilinx ISE Makefile
 ##
 ## To the extent possible under law, the author(s) have dedicated all copyright
 ## and related and neighboring rights to this software to the public domain
 ## worldwide. This software is distributed without any warranty.
+###########################################################################
 
 include project.cfg
 
+
+###########################################################################
+# Default values
+###########################################################################
+
 ifndef XILINX
     $(error XILINX must be defined)
 endif
@@ -28,6 +35,8 @@ NGDBUILD_OPTS   ?=
 MAP_OPTS        ?=
 PAR_OPTS        ?=
 BITGEN_OPTS     ?=
+TRACE_OPTS      ?=
+FUSE_OPTS       ?= -incremental
 
 PROGRAMMER      ?= none
 
@@ -38,13 +47,39 @@ DJTG_DEVICE     ?= DJTG_DEVICE-NOT-SET
 DJTG_INDEX      ?= 0
 
 XC3SPROG_EXE    ?= xc3sprog
-XC3SPROG_CABLE  ?= -c none
+XC3SPROG_CABLE  ?= none
 XC3SPROG_OPTS   ?=
 
+
+###########################################################################
+# Internal variables, platform-specific definitions, and macros
 ###########################################################################
 
+ifeq ($(OS),Windows_NT)
+    XILINX := $(shell cygpath -m $(XILINX))
+    CYG_XILINX := $(shell cygpath $(XILINX))
+    EXE := .exe
+    XILINX_PLATFORM ?= nt64
+    PATH := $(PATH):$(CYG_XILINX)/bin/$(XILINX_PLATFORM)
+else
+    EXE :=
+    XILINX_PLATFORM ?= lin64
+    PATH := $(PATH):$(XILINX)/bin/$(XILINX_PLATFORM)
+endif
+
+TEST_NAMES = $(foreach file,$(VTEST) $(VHDTEST),$(basename $(file)))
+TEST_EXES = $(foreach test,$(TEST_NAMES),build/isim_$(test)$(EXE))
+
 RUN = @echo -ne "\n\n\e[1;33m======== $(1) ========\e[m\n\n"; \
-	cd build && $(XILINX)/$(1)
+	cd build && $(XILINX)/bin/$(XILINX_PLATFORM)/$(1)
+
+# isim executables don't work without this
+export XILINX
+
+
+###########################################################################
+# Default build
+###########################################################################
 
 default: $(BITFILE)
 
@@ -58,6 +93,12 @@ build/$(PROJECT).prj: project.cfg
 	@$(foreach file,$(VSOURCE),echo "verilog work \"../$(file)\"" >> $@;)
 	@$(foreach file,$(VHDSOURCE),echo "vhdl work \"../$(file)\"" >> $@;)
 
+build/$(PROJECT)_sim.prj: build/$(PROJECT).prj
+	@cp build/$(PROJECT).prj $@
+	@$(foreach file,$(VTEST),echo "verilog work \"../$(file)\"" >> $@;)
+	@$(foreach file,$(VHDTEST),echo "vhdl work \"../$(file)\"" >> $@;)
+	@echo "verilog work $(XILINX)/verilog/src/glbl.v" >> $@
+
 build/$(PROJECT).scr: project.cfg
 	@echo "Updating $@"
 	@mkdir -p build
@@ -88,6 +129,39 @@ $(BITFILE): project.cfg $(VSOURCE) $(CONSTRAINTS) build/$(PROJECT).prj build/$(P
 	    -w $(PROJECT).ncd $(PROJECT).bit
 	@echo -ne "\e[1;32m======== OK ========\e[m\n"
 
+
+###########################################################################
+# Testing (work in progress)
+###########################################################################
+
+trace: project.cfg $(BITFILE)
+	$(call RUN,trce) $(COMMON_OPTS) $(TRACE_OPTS) \
+	    $(PROJECT).ncd $(PROJECT).pcf
+
+test: $(TEST_EXES)
+
+build/isim_%$(EXE): build/$(PROJECT)_sim.prj $(VSOURCE) $(VHDSOURCE) $(VTEST) $(VHDTEST)
+	$(call RUN,fuse) $(COMMON_OPTS) $(FUSE_OPTS) \
+	    -prj $(PROJECT)_sim.prj \
+	    -o isim_$*$(EXE) \
+	    work.$* work.glbl
+
+#FIXME TB ?= $(error Must set TB to name of a testbench module)
+
+isim: build/isim_$(TB)$(EXE)
+	@echo "run all" >> build/isim_$(TB).cmd
+	cd build ; ./isim_$(TB)$(EXE) -tclbatch isim_$(TB).cmd
+
+isimgui: build/isim_$(TB)$(EXE)
+	@grep --no-filename --no-messages 'ISIM:' $(TB).{v,vhd} | cut -d: -f2 > build/isim_$(TB).cmd
+	@echo "run all" >> build/isim_$(TB).cmd
+	cd build ; ./isim_$(TB)$(EXE) -gui -tclbatch isim_$(TB).cmd
+
+
+###########################################################################
+# Programming
+###########################################################################
+
 ifeq ($(PROGRAMMER), impact)
 prog: $(BITFILE)
 	$(XILINX)/impact -batch $(IMPACT_OPTS)
@@ -100,7 +174,7 @@ endif
 
 ifeq ($(PROGRAMMER), xc3sprog)
 prog: $(BITFILE)
-	$(XC3SPROG_EXE) $(XC3SPROG_CABLE) $(XC3SPROG_OPTS) $(BITFILE)
+	$(XC3SPROG_EXE) -c $(XC3SPROG_CABLE) $(XC3SPROG_OPTS) $(BITFILE)
 endif
 
 ifeq ($(PROGRAMMER), none)
@@ -108,4 +182,7 @@ prog:
 	$(error PROGRAMMER must be set to use 'make prog')
 endif
 
+
+###########################################################################
+
 # vim: set filetype=make: #
diff --git a/README.md b/README.md
index 4e50610..849b5ef 100644
--- a/README.md
+++ b/README.md
@@ -35,9 +35,9 @@ it consists of `KEY = value` pairs. It must define at least the following keys:
 
     The path to the appropriate binaries directory of the target Xilinx ISE
     install, e.g.
-    `/cygdrive/c/Xilinx/14.7/ISE_DS/ISE/bin/nt64`
+    `/cygdrive/c/Xilinx/14.7/ISE_DS/ISE`
     or
-    `/opt/Xilinx/14.7/ISE_DS/ISE/bin/lin64`
+    `/opt/Xilinx/14.7/ISE_DS/ISE`
     for typical installs.
 
   * `VSOURCE` and/or `VHDSOURCE`
@@ -61,6 +61,13 @@ A simple `project.cfg` may thus resemble:
 
 A number of other keys can be set in the project configuration, including:
 
+  * `XILINX_PLATFORM`
+
+    The Xilinx name for the platform to build for, e.g. `nt64` or `lin`.
+    `nt64` is used by default for Windows systems, and `lin64` for Linux
+    systems, so you only need to set this if you explicitly need to use the
+    32-bit version of the tools for some reason.
+
   * `TOPLEVEL`
 
     The name of the top-level module to be used in the project.
@@ -76,7 +83,8 @@ A number of other keys can be set in the project configuration, including:
     Extra command-line options to be passed to all ISE executables. Defaults to
     `-intstyle xflow`.
 
-  * `XST_OPTS`, `NGDBUILD_OPTS`, `MAP_OPTS`, `PAR_OPTS`, `BITGEN_OPTS`
+  * `XST_OPTS`, `NGDBUILD_OPTS`, `MAP_OPTS`, `PAR_OPTS`, `BITGEN_OPTS`,
+    `TRACE_OPTS`, `FUSE_OPTS`
 
     Extra command-line options to be passed to the corresponding ISE tools. All
     default to empty.
@@ -141,14 +149,18 @@ The Xilinx ISE Makefile implements the following targets:
     configuration; see below for details.
 
 
+Running unit tests
+------------------
+
+is a work in progress.
+
+
 Unimplemented features
 ----------------------
 
 The following features are not currently implemented. (Pull requests are
 encouraged!)
 
-  * Building and/or running testbenches
-
   * Generation of SPI or other unusual programming files
 
   * CPLD synthesis