[LICENSE] Add SPDX Identifier
diff --git a/verilog/rtl/counter_timer_low.v b/verilog/rtl/counter_timer_low.v
index 7dd30bc..074fab4 100755
--- a/verilog/rtl/counter_timer_low.v
+++ b/verilog/rtl/counter_timer_low.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
 /* Simple 32-bit counter-timer for Caravel. */