From 4b4f10f5e67eda57de79b521fa8757cd750ee179 Mon Sep 17 00:00:00 2001
From: Todd Strader <todd.strader@gmail.com>
Date: Fri, 21 Feb 2020 05:47:00 -0500
Subject: [PATCH] Follow other clock gating examples

---
 test_regress/t/t_prot_lib.v            | 20 +++++++++++++++++---
 test_regress/t/t_prot_lib_clk_gated.pl |  1 +
 test_regress/t/t_prot_lib_secret.v     | 14 +++++++++++++-
 3 files changed, 31 insertions(+), 4 deletions(-)

diff --git a/test_regress/t/t_prot_lib.v b/test_regress/t/t_prot_lib.v
index ce80add05..b8bb19ff2 100644
--- a/test_regress/t/t_prot_lib.v
+++ b/test_regress/t/t_prot_lib.v
@@ -14,7 +14,7 @@ if (cyc > 0 && sig``_in != sig``_out) begin \
      $stop; \
        end
 
-module t (/*AUTOARG*/
+module t #(parameter GATED_CLK = 0) (/*AUTOARG*/
           // Inputs
           clk
           );
@@ -90,8 +90,6 @@ module t (/*AUTOARG*/
             cyc <= cyc + 1;
             crc <= {crc[62:0], crc[63]^crc[2]^crc[0]};
             accum_in <= accum_in + 5;
-            // 7 is the secret_value inside the secret module
-            accum_out_expect <= accum_in + accum_out_expect + 7;
             `DRIVE(s1)
             `DRIVE(s2)
             `DRIVE(s8)
@@ -125,6 +123,22 @@ module t (/*AUTOARG*/
             end
          end
 
+         logic possibly_gated_clk;
+         if (GATED_CLK != 0) begin: yes_gated_clock
+             logic clk_en_latch /*verilator clock_enable*/;
+             /* verilator lint_off COMBDLY */
+             always_comb if (clk == '0) clk_en_latch <= clk_en;
+             /* verilator lint_on COMBDLY */
+             assign possibly_gated_clk = clk & clk_en_latch;
+         end else begin: no_gated_clock
+             assign possibly_gated_clk = clk;
+         end
+
+         always @(posedge possibly_gated_clk) begin
+            // 7 is the secret_value inside the secret module
+            accum_out_expect <= accum_in + accum_out_expect + 7;
+         end
+
          always @(*) begin
             // XSim (and maybe all event simulators?) sees the moment where
             // s1_in has not yet propagated to s1_out, however, they do always
diff --git a/test_regress/t/t_prot_lib_clk_gated.pl b/test_regress/t/t_prot_lib_clk_gated.pl
index 9862323a7..394bc08b9 100755
--- a/test_regress/t/t_prot_lib_clk_gated.pl
+++ b/test_regress/t/t_prot_lib_clk_gated.pl
@@ -49,6 +49,7 @@ while (1) {
 
     compile(
         verilator_flags2 => ["$secret_dir/secret.sv",
+                             "-GGATED_CLK=1",
                              "-LDFLAGS",
                              "'-L$secret_prefix -lsecret -static'"],
         xsim_flags2 => ["$secret_dir/secret.sv"],
diff --git a/test_regress/t/t_prot_lib_secret.v b/test_regress/t/t_prot_lib_secret.v
index 05ca43e1b..85c3d5196 100644
--- a/test_regress/t/t_prot_lib_secret.v
+++ b/test_regress/t/t_prot_lib_secret.v
@@ -32,7 +32,19 @@ module secret #(parameter GATED_CLK = 0)
 
    initial $display("created %m");
 
-   wire the_clk = GATED_CLK != 0 ? clk & clk_en : clk;
+   logic the_clk;
+   generate
+      if (GATED_CLK != 0) begin: yes_gated_clock
+          logic clk_en_latch /*verilator clock_enable*/;
+          /* verilator lint_off COMBDLY */
+          always_comb if (clk == '0) clk_en_latch <= clk_en;
+          /* verilator lint_on COMBDLY */
+          assign the_clk = clk & clk_en_latch;
+      end else begin: no_gated_clock
+          assign the_clk = clk;
+      end
+   endgenerate
+
    always @(posedge the_clk) begin
       secret_accum_q <= secret_accum_q + accum_in + secret_value;
    end