[dv] Change performance counter access to DPI

DPI access is suggested and more generic than Verilator direct signal
access. This changes the access to the performance counters from the
Verilator testbench to use DPI instead of directly accessing the
array.

Signed-off-by: Stefan Wallentowitz <stefan.wallentowitz@hm.edu>

dv/verilator/pcount/cpp/ibex_pcounts.cc

@@ -7,6 +7,12 @@
 #include <string>
 #include <vector>
 
+#include <svdpi.h>
+
+extern "C" {
+extern long long mhpmcounter_get(int index);
+}
+
 #include "ibex_pcounts.h"
 
 // see mhpmcounter_incr signals in rtl/ibex_cs_registers.sv for details
@@ -26,7 +32,7 @@ const std::vector<std::string> ibex_counter_names = {
     "Multiply Wait",
     "Divide Wait"};
 
-std::string ibex_pcount_string(uint64_t pcounts[], bool csv) {
+std::string ibex_pcount_string(bool csv) {
   char seperator = csv ? ',' : ':';
   std::string::size_type longest_name_length;
 
@@ -52,7 +58,7 @@ std::string ibex_pcount_string(uint64_t pcounts[], bool csv) {
         pcount_ss << ' ';
     }
 
-    pcount_ss << pcounts[i] << std::endl;
+    pcount_ss << mhpmcounter_get(i) << std::endl;
   }
 
   return pcount_ss.str();

dv/verilator/pcount/cpp/ibex_pcounts.h

@@ -34,11 +34,9 @@ extern const std::vector<std::string> ibex_counter_names;
  * longercountername1: 43980
  * ...
  *
- * @param pcounts Array of performance counter values, must be of length
- *                ibex_pcount_num
  * @param csv Choose csv or pretty-print formatting
  * @return String of formatted performance counter values, newline at end
  */
-std::string ibex_pcount_string(uint64_t pcounts[], bool csv);
+std::string ibex_pcount_string(bool csv);
 
 #endif  // IBEX_PCOUNTS_H_

examples/simple_system/ibex_simple_system.cc

@@ -28,17 +28,19 @@ int main(int argc, char **argv) {
     return 1;
   }
 
+  // Set the scope to the root scope, the ibex_pcount_string function otherwise
+  // doesn't know the scope itself. Could be moved to ibex_pcount_string, but
+  // would require a way to set the scope name from here, similar to MemUtil.
+  svSetScope(svGetScopeFromName("TOP.ibex_simple_system"));
   // TODO: Exec can return with "true" (e.g. with `-h`), but that does not mean
   // `RunSimulation()` was executed. The folllowing values will not be useful
   // in this case.
   std::cout << "\nPerformance Counters" << std::endl
             << "====================" << std::endl;
-  std::cout << ibex_pcount_string(top.ibex_simple_system__DOT__mhpmcounter_vals,
-                                  false);
+  std::cout << ibex_pcount_string(false);
 
   std::ofstream pcount_csv("ibex_simple_system_pcount.csv");
-  pcount_csv << ibex_pcount_string(
-      top.ibex_simple_system__DOT__mhpmcounter_vals, true);
+  pcount_csv << ibex_pcount_string(true);
 
   return 0;
 }

examples/simple_system/rtl/ibex_simple_system.sv

@@ -249,12 +249,10 @@ module ibex_simple_system (
       .timer_intr_o   (timer_irq)
     );
 
-  // Expose the performance counter array so it's easy to access in
-  // a verilator siumulation
-  logic [63:0] mhpmcounter_vals [32] /*verilator public_flat*/;
+  export "DPI-C" function mhpmcounter_get;
+
+  function automatic longint mhpmcounter_get(int index);
+    return u_core.u_ibex_core.cs_registers_i.mhpmcounter[index];
+  endfunction
 
-  for(genvar i = 0;i < 32; i = i + 1) begin
-      assign mhpmcounter_vals[i] = u_core.u_ibex_core.cs_registers_i.mhpmcounter[i];
-  end
 endmodule
-