Use DPIC-function to return deferred result (#250)

Before this commit, we fetch simv_result at 5000 cycles. Only
when the result is not zero, it works and stop simulation.

Now we use DPIC function to implement the return of simv_result when not
zero, so only one DPIC function will be used to stop simulation.
That will reduce the cost of fetch and get result return faster.

src/test/csrc/vcs/vcs_main.cpp

@@ -22,6 +22,9 @@
 #include "ram.h"
 #include "flash.h"
 #include "refproxy.h"
+#ifdef CONFIG_DIFFTEST_DEFERRED_RESULT
+#include "svdpi.h"
+#endif // CONFIG_DIFFTEST_DEFERRED_RESULT
 
 static bool has_reset = false;
 static char bin_file[256] = "ram.bin";
@@ -90,19 +93,37 @@ extern "C" int simv_step() {
   }
 }
 
-#ifdef TB_DEFERRED_RESULT
+#ifdef CONFIG_DIFFTEST_DEFERRED_RESULT
+svScope deferredResultScope;
+extern "C" void set_deferred_result_scope();
+void set_deferred_result_scope() {
+  deferredResultScope = svGetScope();
+}
+
+extern "C" void set_deferred_result();
+void difftest_deferred_result() {
+  if (deferredResultScope == NULL) {
+    printf("Error: Could not retrieve deferred result scope, set first\n");
+    assert(deferredResultScope);
+  }
+  svSetScope(deferredResultScope);
+  set_deferred_result();
+}
+
 static int simv_result = 0;
 extern "C" void simv_nstep(uint8_t step) {
   if (simv_result)
     return;
   for (int i = 0; i < step; i++) {
     int ret = simv_step();
-    if (ret)
-      simv_result = ret;
+    if (ret) {
+        simv_result = ret;
+        break;
+    }
+  }
+  if (simv_result) {
+    difftest_deferred_result();
   }
-}
-extern "C" int simv_result_fetch() {
-  return simv_result;
 }
 #else
 extern "C" int simv_nstep(uint8_t step) {
@@ -113,4 +134,4 @@ extern "C" int simv_nstep(uint8_t step) {
   }
   return 0;
 }
-#endif // TB_DEFERRED_RESULT
+#endif // CONFIG_DIFFTEST_DEFERRED_RESULT

src/test/vsrc/vcs/DeferredControl.v

@@ -7,38 +7,32 @@ module DeferredControl(
   output reg simv_result
 );
 
-import "DPI-C" function int simv_result_fetch();
 import "DPI-C" function void simv_nstep(int step);
+import "DPI-C" context function void set_deferred_result_scope();
+
+initial begin
+  set_deferred_result_scope();
+  simv_result = 1'b0;
+end
+
+export "DPI-C" function set_deferred_result;
+function void set_deferred_result();
+  simv_result = 1'b1;
+endfunction
 
 `ifdef CONFIG_DIFFTEST_NONBLOCK
 `ifdef PALLADIUM
 initial $ixc_ctrl("gfifo", "simv_nstep");
 `endif // PALLADIUM
 `endif // CONFIG_DIFFTEST_NONBLOCK
 
-reg [63:0] fetch_cycles;
-initial fetch_cycles = 4999;
+`ifdef PALLADIUM
+initial $ixc_ctrl("sfifo", "set_deferred_result");
+`endif // PALLADIUM
 
-reg [63:0] fetch_timer;
 always @(posedge clock) begin
-  if (reset) begin
-    simv_result <= 1'b0;
-    fetch_timer <= 64'b0;
-  end
-  else begin
-    if (fetch_timer == fetch_cycles) begin
-      fetch_timer <= 1'b0;
-      if (simv_result_fetch()) begin
-        simv_result <= 1'b1;
-      end
-    end
-    else begin
-      fetch_timer <= fetch_timer + 64'b1;
-    end
-
-    if ((~simv_result) && (|step)) begin
-      simv_nstep(step);
-    end
+  if (!reset && !simv_result && step != 0) begin
+    simv_nstep(step);
   end
 end