sras: improve segmented RAS ressource usage

Signed-off-by: Alban Gruin <alban.gruin@irit.fr>

src/frontend/sras.sv

@@ -48,13 +48,19 @@ module sras #(
     assign pp_plus_one = tos_q[ptr_spec_q] + 1'b1;
     assign prev_minus_one = previous_tos - 1'b1;
 
-    for (genvar i = 0; i < SpecDepth; i++) begin
-        assign tos_d[i] = (flush_i) ? '0 :
-                          (i == ptr_spec_d && push_i && !pop_i) ? prev_plus_one :
-                          (i == ptr_spec_q && push_i && !pop_i) ? pp_plus_one :
-                          (i == ptr_spec_d && !push_i && pop_i) ? prev_minus_one :
-                          (i == ptr_spec_d && !bad_spec_i && begin_spec_i) ? tos_q[ptr_spec_q] :
-                          tos_q[i];
+    always_comb begin
+        tos_d = tos_q;
+
+        if (flush_i) begin
+            tos_d = '0;
+        end else if (push_i && !pop_i) begin
+            tos_d[ptr_spec_d] = prev_plus_one;
+            tos_d[ptr_spec_q] = pp_plus_one;
+        end else if (!push_i && pop_i) begin
+            tos_d[ptr_spec_d] = prev_minus_one;
+        end else if (!bad_spec_i && begin_spec_i) begin
+            tos_d[ptr_spec_d] = tos_q[ptr_spec_q];
+        end
     end
 
     assign data_o = stack_q[previous_tos_addr][previous_tos];
@@ -65,14 +71,28 @@ module sras #(
 
     ariane_pkg::ras_t [DEPTH-1:0] new_stack, prev_stack;
 
-    for (genvar i = 0; i < DEPTH; i++) begin
-        assign new_stack[i] = ((i == previous_tos && pop_i) ||
-                               (i == prev_plus_one && push_i)) ? to_push :
-                              (!bad_spec_i && begin_spec_i) ? stack_q[ptr_spec_q][i] :
-                              stack_q[ptr_spec_d][i];
+    always_comb begin
+        new_stack = stack_q[ptr_spec_d];
+
+        if (!bad_spec_i && begin_spec_i) begin
+            new_stack = stack_q[ptr_spec_q];
+        end
+
+        if (pop_i) begin
+            new_stack[previous_tos] = to_push;
+        end
 
-        assign prev_stack[i] = (i == pp_plus_one && push_i) ? to_push :
-                               stack_q[ptr_spec_q][i];
+        if (push_i) begin
+            new_stack[prev_plus_one] = to_push;
+        end
+    end
+
+    always_comb begin
+        prev_stack = stack_q[ptr_spec_q];
+
+        if (push_i) begin
+            prev_stack[pp_plus_one] = to_push;
+        end
     end
 
     for (genvar i = 0; i < SpecDepth; i++) begin