Fix VCS VCD generation

Signed-off-by: Michal Czyz <[email protected]>

vcs/defs.bzl

@@ -144,7 +144,7 @@ def _vcs_run(ctx):
     # Waveform
     if ctx.attr.trace:
         trace_file = ctx.actions.declare_file("{}.vcd".format(ctx.label.name))
-        args.extend(["-vcd", trace_file.path])
+        args.extend(["+vcd="+trace_file.path])
         args.append("+vcs+dumpon+0+0")
         args.append("+vcs+dumparrays")
         outputs.append(trace_file)

vcs/tests/BUILD

@@ -0,0 +1,64 @@
+# Copyright 2025 bazel_rules_hdl Authors
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+load("@rules_cc//cc:defs.bzl", "cc_test")
+load("//vcs:defs.bzl", "vcs_binary", "vcs_run")
+load("//verilog:defs.bzl", "verilog_library")
+
+package(
+    default_applicable_licenses = ["//:package_license"],
+    default_visibility = ["//visibility:private"],
+)
+
+verilog_library(
+    name = "adder",
+    srcs = [
+        "adder.sv",
+    ],
+)
+
+
+verilog_library(
+    name = "tb",
+    srcs = [
+        "tb.sv",
+    ],
+    deps = [
+        ":adder",
+    ],
+)
+
+vcs_binary(
+    name = "tb_vcs",
+    vcs_env = "//vcs/tests:vcs_env.sh",
+    module = ":tb",
+    module_top = "tb",
+    opts = [
+        "-full64",
+        "+vcs+lic+wait",
+        "+error+500",
+    ],
+    visibility = [
+        "//visibility:public",
+    ],
+)
+
+vcs_run(
+    name = "tb_vcs_run",
+    binary = ":tb_vcs",
+    trace = True,
+    visibility = [
+        "//visibility:public",
+    ],
+)

vcs/tests/README.md

@@ -0,0 +1,3 @@
+# VCS test
+
+You need to update variables in the `vcs_env.sh` file before running the tests.

vcs/tests/adder.sv

@@ -0,0 +1,29 @@
+// Copyright 2025 bazel_rules_hdl Authors
+//
+//Licensed under the Apache License, Version 2.0 (the "License");
+//you may not use this file except in compliance with the License.
+//You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+//Unless required by applicable law or agreed to in writing, software
+//distributed under the License is distributed on an "AS IS" BASIS,
+//WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+//See the License for the specific language governing permissions and
+//limitations under the License.
+
+
+module adder (
+    input [7:0] x,
+    input [7:0] y,
+    input carry_in,
+    output carry_output_bit,
+    output [7:0] sum
+);
+  logic [8:0] result;
+  /* verilator lint_off WIDTH */
+  assign result = x + y + carry_in;
+  /* verilator lint_on WIDTH */
+  assign sum = result[7:0];
+  assign carry_output_bit = result[8];
+endmodule

vcs/tests/tb.sv

@@ -0,0 +1,44 @@
+// Copyright 2025 bazel_rules_hdl Authors
+
+module tb ();
+
+  // Waveform
+  initial begin : proc_waveform
+    string vcd_file = "dump.vcd";
+    if ($value$plusargs("vcd=%s", vcd_file)) begin
+      $display(vcd_file);
+      $dumpfile(vcd_file);
+      $dumpvars();
+    end
+  end
+
+  // DUT
+  logic [7:0] x;
+  logic [7:0] y;
+  logic carry_in;
+  logic carry_output_bit;
+  logic [7:0] sum;
+
+  adder dut (
+      .x(x),
+      .y(y),
+      .carry_in(carry_in),
+      .carry_output_bit(carry_output_bit),
+      .sum(sum)
+  );
+
+  // Test procedure
+  initial begin : proc_test
+    x = 0;
+    y = 0;
+    carry_in = 0;
+    $display("Testing adder:");
+    #10 x = 1;
+    y = 2;
+    #10 $display("x=%d, y=%d, x+y=%d", x, y, sum);
+    assert (sum == 3);
+    #10 $display("Testing done.");
+    $finish();
+  end
+
+endmodule

vcs/tests/vcs_env.sh

@@ -0,0 +1,6 @@
+#!/bin/bash
+# Copyright 2025 bazel_rules_hdl Authors
+
+export LM_LICENSE_FILE=<lm_license_file>
+export VCS_HOME=<vcs_home>
+export PATH=$VCS_HOME/bin:$PATH