rtl: Add manual buffer to scan_wrapper

Looking at results from different projects, the buffering on those
is a bit inconsitent. So instead we make our own so that hopefully
it's the same for all projects.

Signed-off-by: Sylvain Munaut <[email protected]>

Author: smunaut

template/scan_wrapper.v

@@ -19,11 +19,29 @@ module scan_wrapper_USER_MODULE_ID (
     output wire scan_select_out,
     output wire latch_enable_out
     );
-    
-    assign scan_select_out = scan_select_in;
-    assign latch_enable_out = latch_enable_in;
-    assign clk_out = clk_in;
-    wire clk = clk_in;
+
+    // input buffers
+        // Looking at results from multiple projects the bufferring is a bit
+        // inconsistent. So instead, we ensure at least clk buf
+    wire clk;
+
+    sky130_fd_sc_hd__clkbuf_2 input_buf_clk (
+        .A          (clk_in),
+        .X          (clk),
+        .VPWR       (1'b1),
+        .VGND       (1'b0)
+    );
+
+    // output buffers
+        // Same as for input, to try and be more consistent, we make our own
+    wire data_out_i;
+
+    sky130_fd_sc_hd__buf_4 output_buffers[3:0] (
+        .A          ({clk,     data_out_i, scan_select_in,  latch_enable_in }),
+        .X          ({clk_out, data_out,   scan_select_out, latch_enable_out }),
+        .VPWR       (1'b1),
+        .VGND       (1'b0)
+    );
 
     /*
     `ifdef COCOTB
@@ -51,7 +69,7 @@ module scan_wrapper_USER_MODULE_ID (
         .RESET_B    (1'b1),
         .CLK_N      (clk),
         .D          (scan_data_out[NUM_IOS-1]),
-        .Q          (data_out),
+        .Q          (data_out_i),
         .VPWR       (1'b1),
         .VGND       (1'b0)
     );