[otbn,dv] Tidy up timing waiting for call stack corruption errors

The existing code looked at a stack_read_o output from the stack, but
that isn't quite what we want because it only goes high if the
instruction is actually committed. This might not happen, in which
case we'll request a stack pop but tell the stack not to commit the
change. But we still expect to see an error immediately. Make the
timing line up.

Signed-off-by: Rupert Swarbrick <rswarbrick@lowrisc.org>

hw/ip/otbn/dv/uvm/env/seq_lib/otbn_stack_addr_integ_chk_vseq.sv

@@ -61,8 +61,12 @@ class otbn_stack_addr_integ_chk_vseq extends otbn_single_vseq;
     cfg.model_agent_cfg.vif.send_err_escalation(32'd1 << 20);
   endtask
 
+  task wait_for_call_stack_read(string rf_base_path);
+    wait_for_flag({rf_base_path, ".pop_stack_reqd"});
+  endtask
+
   task inject_integ_err();
-    string       stack_path;
+    string       base_path, stack_path;
     bit          stack_nonempty;
     int unsigned msb;
     string       forced_paths[$];
@@ -73,12 +77,13 @@ class otbn_stack_addr_integ_chk_vseq extends otbn_single_vseq;
 
     if (err_type) begin
       // We want to inject an error into the call stack (the data backing x1)
-      stack_path = "tb.dut.u_otbn_core.u_otbn_rf_base.u_call_stack";
+      base_path = "tb.dut.u_otbn_core.u_otbn_rf_base";
+      stack_path = {base_path, ".u_call_stack"};
       msb = 38;
     end else begin
       // We want to inject an error into the loop stack
-      stack_path = {"tb.dut.u_otbn_core.",
-                    "u_otbn_controller.u_otbn_loop_controller.loop_info_stack"};
+      base_path = "tb.dut.u_otbn_core.u_otbn_controller.u_otbn_loop_controller";
+      stack_path = {base_path, ".loop_info_stack"};
       msb = 34;
     end
 
@@ -107,7 +112,7 @@ class otbn_stack_addr_integ_chk_vseq extends otbn_single_vseq;
           if (err_type) begin
             // We have just injected an error into the call stack. Wait until it gets read back
             // again and then tell the model about the expected error.
-            wait_for_flag({stack_path, ".stack_read_o"});
+            wait_for_call_stack_read(base_path);
             send_escalation_to_model();
           end else begin
             // A loop stack corruption should actually have become visible immediately, so we do the