[LICENSE] Add SPDX Identifier
diff --git a/verilog/rtl/convert_gpio_sigs.v b/verilog/rtl/convert_gpio_sigs.v
index c9aeefa..b197c7d 100644
--- a/verilog/rtl/convert_gpio_sigs.v
+++ b/verilog/rtl/convert_gpio_sigs.v
@@ -11,6 +11,7 @@
// 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.
+// SPDX-License-Identifier: Apache-2.0
`default_nettype none
/* Convert the standard set of GPIO signals: input, output, output_enb,
