diff --git a/.gitignore b/.gitignore
index 2022211..957c3ef 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,2 +1 @@
-obj_dir
-*mode[01][01].*
+simtop_*
diff --git a/COPYING_OHL b/COPYING_OHL
new file mode 100644
index 0000000..7c98175
--- /dev/null
+++ b/COPYING_OHL
@@ -0,0 +1,311 @@
+CERN Open Hardware Licence Version 2 - Weakly Reciprocal
+
+
+Preamble
+
+CERN has developed this licence to promote collaboration among
+hardware designers and to provide a legal tool which supports the
+freedom to use, study, modify, share and distribute hardware designs
+and products based on those designs. Version 2 of the CERN Open
+Hardware Licence comes in three variants: CERN-OHL-P (permissive); and
+two reciprocal licences: this licence, CERN-OHL-W (weakly reciprocal)
+and CERN-OHL-S (strongly reciprocal).
+
+The CERN-OHL-W is copyright CERN 2020. Anyone is welcome to use it, in
+unmodified form only.
+
+Use of this Licence does not imply any endorsement by CERN of any
+Licensor or their designs nor does it imply any involvement by CERN in
+their development.
+
+
+1 Definitions
+
+  1.1 'Licence' means this CERN-OHL-W.
+
+  1.2 'Compatible Licence' means
+
+       a) any earlier version of the CERN Open Hardware licence, or
+
+       b) any version of the CERN-OHL-S or the CERN-OHL-W, or
+
+       c) any licence which permits You to treat the Source to which
+          it applies as licensed under CERN-OHL-S or CERN-OHL-W
+          provided that on Conveyance of any such Source, or any
+          associated Product You treat the Source in question as being
+          licensed under CERN-OHL-S or CERN-OHL-W as appropriate.
+
+  1.3 'Source' means information such as design materials or digital
+      code which can be applied to Make or test a Product or to
+      prepare a Product for use, Conveyance or sale, regardless of its
+      medium or how it is expressed. It may include Notices.
+
+  1.4 'Covered Source' means Source that is explicitly made available
+      under this Licence.
+
+  1.5 'Product' means any device, component, work or physical object,
+      whether in finished or intermediate form, arising from the use,
+      application or processing of Covered Source.
+
+  1.6 'Make' means to create or configure something, whether by
+      manufacture, assembly, compiling, loading or applying Covered
+      Source or another Product or otherwise.
+
+  1.7 'Available Component' means any part, sub-assembly, library or
+      code which:
+
+       a) is licensed to You as Complete Source under a Compatible
+          Licence; or
+
+       b) is available, at the time a Product or the Source containing
+          it is first Conveyed, to You and any other prospective
+          licensees
+
+           i) with sufficient rights and information (including any
+              configuration and programming files and information
+              about its characteristics and interfaces) to enable it
+              either to be Made itself, or to be sourced and used to
+              Make the Product; or
+          ii) as part of the normal distribution of a tool used to
+              design or Make the Product.
+
+  1.8 'External Material' means anything (including Source) which:
+
+       a) is only combined with Covered Source in such a way that it
+          interfaces with the Covered Source using a documented
+          interface which is described in the Covered Source; and
+
+       b) is not a derivative of or contains Covered Source, or, if it
+          is, it is solely to the extent necessary to facilitate such
+          interfacing.
+
+  1.9 'Complete Source' means the set of all Source necessary to Make
+      a Product, in the preferred form for making modifications,
+      including necessary installation and interfacing information
+      both for the Product, and for any included Available Components.
+      If the format is proprietary, it must also be made available in
+      a format (if the proprietary tool can create it) which is
+      viewable with a tool available to potential licensees and
+      licensed under a licence approved by the Free Software
+      Foundation or the Open Source Initiative. Complete Source need
+      not include the Source of any Available Component, provided that
+      You include in the Complete Source sufficient information to
+      enable a recipient to Make or source and use the Available
+      Component to Make the Product.
+
+ 1.10 'Source Location' means a location where a Licensor has placed
+      Covered Source, and which that Licensor reasonably believes will
+      remain easily accessible for at least three years for anyone to
+      obtain a digital copy.
+
+ 1.11 'Notice' means copyright, acknowledgement and trademark notices,
+      Source Location references, modification notices (subsection
+      3.3(b)) and all notices that refer to this Licence and to the
+      disclaimer of warranties that are included in the Covered
+      Source.
+
+ 1.12 'Licensee' or 'You' means any person exercising rights under
+      this Licence.
+
+ 1.13 'Licensor' means a natural or legal person who creates or
+      modifies Covered Source. A person may be a Licensee and a
+      Licensor at the same time.
+
+ 1.14 'Convey' means to communicate to the public or distribute.
+
+
+2 Applicability
+
+  2.1 This Licence governs the use, copying, modification, Conveying
+      of Covered Source and Products, and the Making of Products. By
+      exercising any right granted under this Licence, You irrevocably
+      accept these terms and conditions.
+
+  2.2 This Licence is granted by the Licensor directly to You, and
+      shall apply worldwide and without limitation in time.
+
+  2.3 You shall not attempt to restrict by contract or otherwise the
+      rights granted under this Licence to other Licensees.
+
+  2.4 This Licence is not intended to restrict fair use, fair dealing,
+      or any other similar right.
+
+
+3 Copying, Modifying and Conveying Covered Source
+
+  3.1 You may copy and Convey verbatim copies of Covered Source, in
+      any medium, provided You retain all Notices.
+
+  3.2 You may modify Covered Source, other than Notices, provided that
+      You irrevocably undertake to make that modified Covered Source
+      available from a Source Location should You Convey a Product in
+      circumstances where the recipient does not otherwise receive a
+      copy of the modified Covered Source. In each case subsection 3.3
+      shall apply.
+
+      You may only delete Notices if they are no longer applicable to
+      the corresponding Covered Source as modified by You and You may
+      add additional Notices applicable to Your modifications.
+
+  3.3 You may Convey modified Covered Source (with the effect that You
+      shall also become a Licensor) provided that You:
+
+       a) retain Notices as required in subsection 3.2;
+
+       b) add a Notice to the modified Covered Source stating that You
+          have modified it, with the date and brief description of how
+          You have modified it;
+
+       c) add a Source Location Notice for the modified Covered Source
+          if You Convey in circumstances where the recipient does not
+          otherwise receive a copy of the modified Covered Source; and
+
+       d) license the modified Covered Source under the terms and
+          conditions of this Licence (or, as set out in subsection
+          8.3, a later version, if permitted by the licence of the
+          original Covered Source). Such modified Covered Source must
+          be licensed as a whole, but excluding Available Components
+          contained in it or External Material to which it is
+          interfaced, which remain licensed under their own applicable
+          licences.
+
+
+4 Making and Conveying Products
+
+  4.1 You may Make Products, and/or Convey them, provided that You
+      either provide each recipient with a copy of the Complete Source
+      or ensure that each recipient is notified of the Source Location
+      of the Complete Source. That Complete Source includes Covered
+      Source and You must accordingly satisfy Your obligations set out
+      in subsection 3.3. If specified in a Notice, the Product must
+      visibly and securely display the Source Location on it or its
+      packaging or documentation in the manner specified in that
+      Notice.
+
+  4.2 Where You Convey a Product which incorporates External Material,
+      the Complete Source for that Product which You are required to
+      provide under subsection 4.1 need not include any Source for the
+      External Material.
+
+  4.3 You may license Products under terms of Your choice, provided
+      that such terms do not restrict or attempt to restrict any
+      recipients' rights under this Licence to the Covered Source.
+
+
+5 Research and Development
+
+You may Convey Covered Source, modified Covered Source or Products to
+a legal entity carrying out development, testing or quality assurance
+work on Your behalf provided that the work is performed on terms which
+prevent the entity from both using the Source or Products for its own
+internal purposes and Conveying the Source or Products or any
+modifications to them to any person other than You. Any modifications
+made by the entity shall be deemed to be made by You pursuant to
+subsection 3.2.
+
+
+6 DISCLAIMER AND LIABILITY
+
+  6.1 DISCLAIMER OF WARRANTY -- The Covered Source and any Products
+      are provided 'as is' and any express or implied warranties,
+      including, but not limited to, implied warranties of
+      merchantability, of satisfactory quality, non-infringement of
+      third party rights, and fitness for a particular purpose or use
+      are disclaimed in respect of any Source or Product to the
+      maximum extent permitted by law. The Licensor makes no
+      representation that any Source or Product does not or will not
+      infringe any patent, copyright, trade secret or other
+      proprietary right. The entire risk as to the use, quality, and
+      performance of any Source or Product shall be with You and not
+      the Licensor. This disclaimer of warranty is an essential part
+      of this Licence and a condition for the grant of any rights
+      granted under this Licence.
+
+  6.2 EXCLUSION AND LIMITATION OF LIABILITY -- The Licensor shall, to
+      the maximum extent permitted by law, have no liability for
+      direct, indirect, special, incidental, consequential, exemplary,
+      punitive or other damages of any character including, without
+      limitation, procurement of substitute goods or services, loss of
+      use, data or profits, or business interruption, however caused
+      and on any theory of contract, warranty, tort (including
+      negligence), product liability or otherwise, arising in any way
+      in relation to the Covered Source, modified Covered Source
+      and/or the Making or Conveyance of a Product, even if advised of
+      the possibility of such damages, and You shall hold the
+      Licensor(s) free and harmless from any liability, costs,
+      damages, fees and expenses, including claims by third parties,
+      in relation to such use.
+
+
+7 Patents
+
+  7.1 Subject to the terms and conditions of this Licence, each
+      Licensor hereby grants to You a perpetual, worldwide,
+      non-exclusive, no-charge, royalty-free, irrevocable (except as
+      stated in subsections 7.2 and 8.4) patent licence to Make, have
+      Made, use, offer to sell, sell, import, and otherwise transfer
+      the Covered Source and Products, where such licence applies only
+      to those patent claims licensable by such Licensor that are
+      necessarily infringed by exercising rights under the Covered
+      Source as Conveyed by that Licensor.
+
+  7.2 If You institute patent litigation against any entity (including
+      a cross-claim or counterclaim in a lawsuit) alleging that the
+      Covered Source or a Product constitutes direct or contributory
+      patent infringement, or You seek any declaration that a patent
+      licensed to You under this Licence is invalid or unenforceable
+      then any rights granted to You under this Licence shall
+      terminate as of the date such process is initiated.
+
+
+8 General
+
+  8.1 If any provisions of this Licence are or subsequently become
+      invalid or unenforceable for any reason, the remaining
+      provisions shall remain effective.
+
+  8.2 You shall not use any of the name (including acronyms and
+      abbreviations), image, or logo by which the Licensor or CERN is
+      known, except where needed to comply with section 3, or where
+      the use is otherwise allowed by law. Any such permitted use
+      shall be factual and shall not be made so as to suggest any kind
+      of endorsement or implication of involvement by the Licensor or
+      its personnel.
+
+  8.3 CERN may publish updated versions and variants of this Licence
+      which it considers to be in the spirit of this version, but may
+      differ in detail to address new problems or concerns. New
+      versions will be published with a unique version number and a
+      variant identifier specifying the variant. If the Licensor has
+      specified that a given variant applies to the Covered Source
+      without specifying a version, You may treat that Covered Source
+      as being released under any version of the CERN-OHL with that
+      variant. If no variant is specified, the Covered Source shall be
+      treated as being released under CERN-OHL-S. The Licensor may
+      also specify that the Covered Source is subject to a specific
+      version of the CERN-OHL or any later version in which case You
+      may apply this or any later version of CERN-OHL with the same
+      variant identifier published by CERN.
+
+      You may treat Covered Source licensed under CERN-OHL-W as
+      licensed under CERN-OHL-S if and only if all Available
+      Components referenced in the Covered Source comply with the
+      corresponding definition of Available Component for CERN-OHL-S.
+
+  8.4 This Licence shall terminate with immediate effect if You fail
+      to comply with any of its terms and conditions.
+
+  8.5 However, if You cease all breaches of this Licence, then Your
+      Licence from any Licensor is reinstated unless such Licensor has
+      terminated this Licence by giving You, while You remain in
+      breach, a notice specifying the breach and requiring You to cure
+      it within 30 days, and You have failed to come into compliance
+      in all material respects by the end of the 30 day period. Should
+      You repeat the breach after receipt of a cure notice and
+      subsequent reinstatement, this Licence will terminate
+      immediately and permanently. Section 6 shall continue to apply
+      after any termination.
+
+  8.6 This Licence shall not be enforceable except by a Licensor
+      acting as such, and third party beneficiary rights are
+      specifically excluded.
diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..e69de29
diff --git a/README.md b/README.md
index 1da0cc8..6fdee35 100644
--- a/README.md
+++ b/README.md
@@ -5,10 +5,13 @@ via parameters.
 
 ## License
 
-This Program is subject to the terms of the Mozilla Public License,
-v.2.0. A copy of this license may be found in the file `COPYING`. You
+All code in this project is licensed to the terms of the Mozilla Public
+License, v.2.0. A copy of this license may be found in the file `COPYING`. You
 can obtain one at https://mozilla.org/MPL/2.0/.
 
+All Verilog source in this project is dual-licensed under the MPL v2.0
+and the CERN-OHL-W v2.0 (or any later version).
+
 ## Tests
 
 Go into `tests` and run `make`. To rerun tests, run `make clean` followed
diff --git a/spi_master.v b/spi_master.v
index cc5f01d..ae75394 100644
--- a/spi_master.v
+++ b/spi_master.v
@@ -31,10 +31,10 @@ spi_master
 `endif
 `ifndef SPI_MASTER_NO_WRITE
 	input [WID-1:0] to_slave,
-	output mosi,
+	output reg mosi,
 `endif
-	output sck_wire,
-	output finished,
+	output reg sck_wire,
+	output reg finished,
 	input arm
 );
 
@@ -141,7 +141,7 @@ always @ (posedge clk) begin
 			timer <= 0;
 			// Stop transfer when the clock returns
 			// to its original polarity.
-			if (bit_counter == WID && sck == POLARITY) begin
+			if (bit_counter == WID[WID_LEN-1:0] && sck == POLARITY[0]) begin
 				state <= WAIT_FINISHED;
 			end else begin
 				state <= ON_CYCLE;
diff --git a/spi_master_no_read.v b/spi_master_no_read.v
new file mode 100644
index 0000000..0999807
--- /dev/null
+++ b/spi_master_no_read.v
@@ -0,0 +1,3 @@
+`define SPI_MASTER_NO_READ
+/* verilator lint_off DECLFILENAME */
+`include "spi_master.v"
diff --git a/spi_slave.v b/spi_slave.v
index 6efacdd..4c15e37 100644
--- a/spi_slave.v
+++ b/spi_slave.v
@@ -77,7 +77,7 @@ task setup_bits();
 endtask
 
 task check_counter();
-	if (bit_counter == WID) begin
+	if (bit_counter == WID[WID_LEN-1:0]) begin
 		err <= ready_at_start;
 	end else begin
 		bit_counter <= bit_counter + 1;
diff --git a/spi_slave_no_write.v b/spi_slave_no_write.v
new file mode 100644
index 0000000..f60ea0b
--- /dev/null
+++ b/spi_slave_no_write.v
@@ -0,0 +1,3 @@
+`define SPI_SLAVE_NO_WRITE
+/* verilator lint_off DECLFILENAME */
+`include "spi_slave.v"
diff --git a/tests/Makefile b/tests/Makefile
deleted file mode 100644
index 085cd92..0000000
--- a/tests/Makefile
+++ /dev/null
@@ -1,10 +0,0 @@
-MODES=00 01 10 11
-
-all:
-	for i in ${MODES}; do \
-		make -f run_mode.makefile MODE="$$i"; \
-		make -f run_mode.makefile MODE="$$i" PREFIX="read_only_" MASTER_TYPE="_no_write" SLAVE_TYPE="_no_read"; \
-	done
-
-clean:
-	rm -rf obj_dir mode[01][01]* read_only_mode[01][01]*
diff --git a/tests/mk.sh b/tests/mk.sh
new file mode 100755
index 0000000..f907668
--- /dev/null
+++ b/tests/mk.sh
@@ -0,0 +1,54 @@
+#!/bin/sh
+
+run_test() {
+	POL=$1
+	PHASE=$2
+	MASTER_TYPE=$3
+	SLAVE_TYPE=$4
+	DIR=$5
+	WID=$6
+	MODS=$7
+	EXTARG=$8
+	WIDLEN=$(printf "import math\nprint(math.floor(math.log2($WID) + 1))" | python3 -)
+
+	verilator --cc --exe -I.. -Wall -Wno-unused --trace \
+		--top-module simtop \
+		-GPOLARITY=$POL -GPHASE=$PHASE -GWID=$WID -CFLAGS -DWID=$WID \
+		-GWID_LEN=$WIDLEN \
+		-DSPI_MASTER_TYPE=$MASTER_TYPE -DSPI_SLAVE_TYPE=$SLAVE_TYPE \
+		--Mdir $DIR \
+		$EXTARG \
+		simtop.v write_read.cpp $MODS
+
+	cd "$DIR"
+	make -f Vsimtop.mk
+	./Vsimtop
+}
+
+for POL in 0 1; do
+	for PHASE in 0 1; do
+		( \
+			run_test $POL $PHASE \
+			spi_master spi_slave \
+			simtop_$POL$PHASE 24 \
+			"../spi_master.v ../spi_slave.v"
+		)
+
+		( \
+			run_test $POL $PHASE \
+			spi_master_no_write spi_slave_no_read \
+			simtop_no_write_$POL$PHASE 24 \
+			"../spi_master_no_write.v ../spi_slave_no_read.v" \
+			"-DSPI_MASTER_NO_WRITE -CFLAGS -DSPI_MASTER_NO_WRITE"
+		)
+
+		( \
+			run_test $POL $PHASE \
+			spi_master_no_read spi_slave_no_write \
+			simtop_no_read_$POL$PHASE 24 \
+			"../spi_master_no_read.v ../spi_slave_no_write.v" \
+			"-DSPI_MASTER_NO_READ -CFLAGS -DSPI_MASTER_NO_READ"
+		)
+
+	done
+done
diff --git a/tests/mode_template.cpp b/tests/mode_template.cpp
deleted file mode 100644
index 4b46fb4..0000000
--- a/tests/mode_template.cpp
+++ /dev/null
@@ -1,3 +0,0 @@
-#include "Vmode@MODE@.h"
-using TopModule = Vmode@MODE@;
-#include "write_read.cpp"
diff --git a/tests/mode_template.v b/tests/mode_template.v
deleted file mode 100644
index 1df59b8..0000000
--- a/tests/mode_template.v
+++ /dev/null
@@ -1,34 +0,0 @@
-/* (c) Peter McGoron 2022
- * This Source Code Form is subject to the terms of the Mozilla Public
- * License, v.2.0. If a copy of the MPL was not distributed with this
- * file, You can obtain one at https://mozilla.org/MPL/2.0/.
- */
-
-module mode@MODE@ (
-	input clk,
-	input [23:0] data_ctrl,
-	input activate,
-	input ss,
-	input rdy,
-	output master_finished
-);
-
-spi_write_read
-#(
-	.POLARITY(@POLARITY@),
-	.PHASE(@PHASE@)
-) base (
-	.clk(clk),
-	.data_ctrl(data_ctrl),
-	.activate(activate),
-	.master_finished(master_finished),
-	.ss(ss),
-	.rdy(rdy)
-);
-
-initial begin
-	$dumpfile("mode@MODE@.vcd");
-	$dumpvars();
-end
-
-endmodule
diff --git a/tests/read_only_mode_template.cpp b/tests/read_only_mode_template.cpp
deleted file mode 100644
index d09a0be..0000000
--- a/tests/read_only_mode_template.cpp
+++ /dev/null
@@ -1,4 +0,0 @@
-#include "Vread_only_mode@MODE@.h"
-using TopModule = Vread_only_mode@MODE@;
-#define READ_ONLY
-#include "write_read.cpp"
diff --git a/tests/read_only_mode_template.v b/tests/read_only_mode_template.v
deleted file mode 100644
index cd10c7d..0000000
--- a/tests/read_only_mode_template.v
+++ /dev/null
@@ -1,57 +0,0 @@
-/* (c) Peter McGoron 2022
- * This Source Code Form is subject to the terms of the Mozilla Public
- * License, v.2.0. If a copy of the MPL was not distributed with this
- * file, You can obtain one at https://mozilla.org/MPL/2.0/.
- */
-
-module read_only_mode@MODE@ (
-	input clk,
-	input activate,
-	input ss,
-	input rdy,
-	output master_finished
-);
-
-wire miso;
-wire sck;
-wire ss_L = !ss;
-reg [23:0] from_slave_data;
-reg finished;
-reg err;
-
-spi_master_no_write
-#(
-	.POLARITY(@POLARITY@),
-	.PHASE(@PHASE@)
-) master (
-	.clk(clk),
-	.from_slave(from_slave_data),
-	.miso(miso),
-	.sck_wire(sck),
-	.finished(master_finished),
-	.arm(activate)
-);
-
-reg [23:0] to_master = 24'hF4325F;
-
-spi_slave_no_read
-#(
-	.POLARITY(@POLARITY@),
-	.PHASE(@PHASE@)
-) slave (
-	.clk(clk),
-	.sck(sck),
-	.ss_L(ss_L),
-	.to_master(to_master),
-	.miso(miso),
-	.finished(finished),
-	.rdy(rdy),
-	.err(finished)
-);
-
-initial begin
-	$dumpfile("read_only_mode@MODE@.vcd");
-	$dumpvars();
-end
-
-endmodule
diff --git a/tests/run_mode.makefile b/tests/run_mode.makefile
deleted file mode 100644
index 2b48053..0000000
--- a/tests/run_mode.makefile
+++ /dev/null
@@ -1,24 +0,0 @@
-# (c) Peter McGoron 2022
-# This Source Code Form is subject to the terms of the Mozilla Public
-# License, v.2.0. If a copy of the MPL was not distributed with this
-# file, You can obtain one at https://mozilla.org/MPL/2.0/.
-
-TESTBENCH_BASE=${PREFIX}mode${MODE}
-AUXFILES=../spi_master${MASTER_TYPE}.v ../spi_slave${SLAVE_TYPE}.v
-
-CPP_TESTBENCH=${TESTBENCH_BASE}.cpp
-WAVEFILE=${TESTBENCH_BASE}.vcd
-
-FILES=${TESTBENCH_BASE}.v ${AUXFILES} ${CPP_TESTBENCH}
-
-${WAVEFILE}: obj_dir/V${TESTBENCH_BASE}
-	./obj_dir/V${TESTBENCH_BASE}
-
-obj_dir/V${TESTBENCH_BASE}.mk: ${FILES}
-	verilator -I.. -Wall -Wno-unused -Wpedantic --trace --cc --exe ${FILES} --top ${TESTBENCH_BASE}
-obj_dir/V${TESTBENCH_BASE}: obj_dir/V${TESTBENCH_BASE}.mk
-	make -C obj_dir -f V${TESTBENCH_BASE}.mk
-${TESTBENCH_BASE}.v: mode_template.v
-	sed "s/@PHASE@/`echo ${MODE} | cut -c 2`/g; s/@POLARITY@/`echo ${MODE} | cut -c 1`/g; s/@MODE@/${MODE}/g" ${PREFIX}mode_template.v > ${TESTBENCH_BASE}.v
-${TESTBENCH_BASE}.cpp: mode_template.cpp
-	sed "s/@PHASE@/`echo ${MODE} | cut -c 2`/g; s/@POLARITY@/`echo ${MODE} | cut -c 1`/g; s/@MODE@/${MODE}/g" ${PREFIX}mode_template.cpp > ${TESTBENCH_BASE}.cpp
diff --git a/tests/simtop.v b/tests/simtop.v
new file mode 100644
index 0000000..91533fd
--- /dev/null
+++ b/tests/simtop.v
@@ -0,0 +1,87 @@
+/* (c) Peter McGoron 2022
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v.2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+module simtop
+#(
+	parameter POLARITY = 0,
+	parameter PHASE = 0,
+	parameter WID = 24,
+	parameter WID_LEN = 5
+) (
+	input clk,
+`ifndef SPI_MASTER_NO_WRITE
+	input [WID-1:0] master_to_slave,
+	output [WID-1:0] from_master,
+`endif
+`ifndef SPI_MASTER_NO_READ
+	input [WID-1:0] slave_to_master,
+	output [WID-1:0] from_slave,
+`endif
+	input activate,
+	input ss,
+	input rdy,
+	output master_finished,
+	output err
+);
+
+`ifndef SPI_MASTER_NO_READ
+wire miso;
+`endif
+
+`ifndef SPI_MASTER_NO_WRITE
+wire mosi;
+`endif
+
+wire sck;
+wire ss_L = !ss;
+
+reg slave_finished;
+reg slave_error;
+
+`SPI_MASTER_TYPE
+#(
+	.POLARITY(POLARITY),
+	.PHASE(PHASE),
+	.WID(WID),
+	.WID_LEN(WID_LEN)
+) master (
+	.clk(clk),
+`ifndef SPI_MASTER_NO_WRITE
+	.to_slave(master_to_slave),
+	.mosi(mosi),
+`endif
+`ifndef SPI_MASTER_NO_READ
+	.from_slave(from_slave),
+	.miso(miso),
+`endif
+	.sck_wire(sck),
+	.finished(master_finished),
+	.arm(activate)
+);
+
+`SPI_SLAVE_TYPE #(
+	.POLARITY(POLARITY),
+	.PHASE(PHASE),
+	.WID(WID),
+	.WID_LEN(WID_LEN)
+) slave (
+	.clk(clk),
+	.sck(sck),
+	.ss_L(ss_L),
+`ifndef SPI_MASTER_NO_WRITE
+	.from_master(from_master),
+	.mosi(mosi),
+`endif
+`ifndef SPI_MASTER_NO_READ
+	.to_master(slave_to_master),
+	.miso(miso),
+`endif
+	.finished(slave_finished),
+	.rdy(rdy),
+	.err(err)
+);
+
+endmodule
diff --git a/tests/spi_write_read.v b/tests/spi_write_read.v
deleted file mode 100644
index efd9e88..0000000
--- a/tests/spi_write_read.v
+++ /dev/null
@@ -1,70 +0,0 @@
-/* (c) Peter McGoron 2022
- * This Source Code Form is subject to the terms of the Mozilla Public
- * License, v.2.0. If a copy of the MPL was not distributed with this
- * file, You can obtain one at https://mozilla.org/MPL/2.0/.
- */
-
-module spi_write_read
-#(
-	parameter POLARITY = 0,
-	parameter PHASE = 0
-)
-(
-	input clk,
-	input [23:0] data_ctrl,
-	input activate,
-	input ss,
-	input rdy,
-	output master_finished
-);
-
-wire miso;
-wire mosi;
-wire sck;
-wire ss_L = !ss;
-
-reg [23:0] from_slave_data;
-reg slave_finished;
-reg slave_error;
-
-spi_master
-#(
-	.POLARITY(POLARITY),
-	.PHASE(PHASE)
-) master (
-	.clk(clk),
-	.to_slave(data_ctrl),
-	.from_slave(from_slave_data),
-	.miso(miso),
-	.mosi(mosi),
-	.sck_wire(sck),
-	.finished(master_finished),
-	.arm(activate)
-);
-
-reg [23:0] data_from_master;
-reg [23:0] data_to_master = 24'b111011011100010101010101;
-
-spi_slave #(
-	.POLARITY(POLARITY),
-	.PHASE(PHASE)
-) slave (
-	.clk(clk),
-	.sck(sck),
-	.ss_L(ss_L),
-	.from_master(data_from_master),
-	.to_master(data_to_master),
-	.mosi(mosi),
-	.miso(miso),
-	.finished(slave_finished),
-	.rdy(rdy),
-	.err(slave_error)
-);
-
-always @ (posedge clk) begin
-	if (slave_finished) begin
-		data_to_master <= data_from_master;
-	end
-end
-
-endmodule
diff --git a/tests/write_read.cpp b/tests/write_read.cpp
index 45bdc5a..2394b63 100644
--- a/tests/write_read.cpp
+++ b/tests/write_read.cpp
@@ -1,12 +1,21 @@
 #include <stdio.h>
 #include <verilated.h>
+#include "Vsimtop.h"
 
-VerilatedContext *ctx;
-TopModule *sim;
+Vsimtop *sim;
+
+uint32_t main_time = 0;
+
+double sc_time_stamp() {
+	return main_time;
+}
 
 static void progress() {
 	sim->eval();
-	ctx->timeInc(1);
+	main_time++;
+	sim->clk = !sim->clk;
+	sim->eval();
+	main_time++;
 	sim->clk = !sim->clk;
 }
 
@@ -15,49 +24,67 @@ static void progress_n(int f) {
 		progress();
 }
 
+static void test_cross_transfer(unsigned m2s, unsigned s2m) {
+#ifndef SPI_MASTER_NO_WRITE
+	sim->master_to_slave = m2s;
+#endif
+#ifndef SPI_MASTER_NO_READ
+	sim->slave_to_master = s2m;
+#endif
+
+	progress();
+	sim->ss = 1;
+	sim->rdy = 1;
+	sim->activate = 1;
+	progress();
+
+	while (!sim->master_finished)
+		progress();
+
+	progress_n(5);
+	sim->activate = 0;
+	sim->ss = 0;
+	sim->rdy = 0;
+	progress_n(5);
+
+	if (sim->err) {
+		printf("slave error\n");
+	}
+
+#ifndef SPI_MASTER_NO_WRITE
+	if (sim->master_to_slave != sim->from_master) {
+		printf("(m2s) %lx != %lx\n", sim->master_to_slave, sim->from_master);
+	}
+#endif
+
+#ifndef SPI_MASTER_NO_READ
+	if (sim->slave_to_master != sim->from_slave) {
+		printf("(m2s) %lx != %lx\n", sim->slave_to_master, sim->from_slave);
+	}
+#endif
+
+}
+
 int main(int argc, char **argv) {
-	ctx = new VerilatedContext;
-	ctx->traceEverOn(true);
-	ctx->commandArgs(argc, argv);
-	sim = new TopModule(ctx);
+	int r = 0;
+	(void)r;
+
+	Verilated::commandArgs(argc, argv);
+	Verilated::traceEverOn(true);
+
+	sim = new Vsimtop;
 	sim->ss = 0;
 	sim->clk = 0;
 	sim->activate = 0;
 	sim->rdy = 0;
 
-	progress_n(8);
-	sim->ss = 1;
-	sim->rdy = 1;
-	progress();
-
-#ifndef READ_ONLY
-	sim->data_ctrl = 0b110011011111001100011111;
-#endif
-	sim->activate = 1;
-
-	while (!sim->master_finished)
-		progress();
-	progress_n(5);
-	sim->activate = 0;
-	sim->ss = 0;
-	sim->rdy = 0;
-	progress_n(5);
-
-#ifndef READ_ONLY
-	sim->data_ctrl = 0xFE3456;
-	sim->activate = 1;
-	sim->ss = 1;
-	sim->rdy = 1;
-	while (!sim->master_finished)
-		progress();
-	progress_n(5);
-	sim->activate = 0;
-	sim->ss = 0;
-	sim->rdy = 0;
-	progress_n(5);
-#endif
+	for (int i = 0; i < 10000; i++) {
+		unsigned m2s = rand() & ((1 << WID) - 1);
+		unsigned s2m = rand() & ((1 << WID) - 1);
+		test_cross_transfer(m2s, s2m);
+	}
 
 	sim->final();
 	delete sim;
-	return 0;
+	return r;
 }