bugfix: x0 should return 0

This commit updates urv_regmem to hardwire x0 to return zero. The previous implementation allowed x0 to be written. The bug was caught using the Riscof architecture test suite which specifically checks for this by writing a value to x0 during at least one of the tests.

bugfix: x0 should return 0
This commit updates urv_regmem to hardwire x0 to return zero. The previous implementation allowed x0 to be written. The bug was caught using the Riscof architecture test suite which specifically checks for this by writing a value to x0 during at least one of the tests.
8b9becd8 · Shareef Jalloq · 65e80de2 · 8b9becd8
Commit 8b9becd8 authored Feb 09, 2024 by Shareef Jalloq
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Showing with 7 additions and 2 deletions

urv_regfile.v rtl/urv_regfile.v +7 -2

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--- a/rtl/urv_regfile.v
+++ b/rtl/urv_regfile.v
@@ -47,8 +47,13 @@ module urv_regmem
   reg [g_width-1:0] 	    ram [0:31];

   always@(posedge clk_i)
-     if(en1_i)
-       q1_o <= ram[a1_i];
+     if(en1_i) begin
+       if(a1_i == 5'd0) begin
+         q1_o <= 32'd0;
+       end else begin
+         q1_o <= ram[a1_i];
+       end
+     end

   always@(posedge clk_i)
     if(we2_i)