Add --slack_redist_iter for ice40

5 files changed, 14 insertions, 8 deletions

diff --git a/common/nextpnr.h b/common/nextpnr.h
index 38a313fd..b163300a 100644
--- a/common/nextpnr.h
+++ b/common/nextpnr.h
@@ -476,6 +476,7 @@ struct Context : Arch, DeterministicRNG
     bool timing_driven = true;
     float target_freq = 12e6;
     bool user_freq = false;
+    int slack_redist_iter = 0;
 
     Context(ArchArgs args) : Arch(args) {}
 
diff --git a/common/placer1.cc b/common/placer1.cc
index f2777a08..278bf466 100644
--- a/common/placer1.cc
+++ b/common/placer1.cc
@@ -237,7 +237,7 @@ class SAPlacer
                 diameter *= post_legalise_dia_scale;
                 ctx->shuffle(autoplaced);
                 assign_budget(ctx);
-            } else {
+            } else if (iter % ctx->slack_redist_iter == 0) {
                 assign_budget(ctx, true /* quiet */);
             }
 
diff --git a/common/router1.cc b/common/router1.cc
index 0bd257fd..5fffbc6d 100644
--- a/common/router1.cc
+++ b/common/router1.cc
@@ -615,8 +615,8 @@ bool router1(Context *ctx)
 
             if (ctx->verbose || iterCnt == 1)
                 log_info("routing queue contains %d jobs.\n", int(jobQueue.size()));
-
-            assign_budget(ctx, true /* quiet */);
+            else if (iterCnt % ctx->slack_redist_iter == 0)
+                assign_budget(ctx, true /* quiet */);
 
             bool printNets = ctx->verbose && (jobQueue.size() < 10);
 
diff --git a/common/timing.cc b/common/timing.cc
index 1d69861b..1b3fd040 100644
--- a/common/timing.cc
+++ b/common/timing.cc
@@ -157,11 +157,12 @@ void assign_budget(Context *ctx, bool quiet)
         }
     }
 
-    // If user has not specified a frequency, dynamically adjust the target 
-    //   frequency to be the current maximum
-    if (!ctx->user_freq) {
+    // For slack redistribution, if user has not specified a frequency
+    //   dynamically adjust the target frequency to be the currently
+    //   achieved maximum
+    if (!ctx->user_freq && ctx->slack_redist_iter > 0) {
         ctx->target_freq = 1e12 / (default_slack - min_slack);
-        if (ctx->verbose)
+        /*if (ctx->verbose)*/
             log_info("minimum slack for this assign = %d, target Fmax for next update = %.2f MHz\n", min_slack,
                      ctx->target_freq / 1e6);
     }
diff --git a/ice40/main.cc b/ice40/main.cc
index 5c9678db..ab672ddc 100644
--- a/ice40/main.cc
+++ b/ice40/main.cc
@@ -105,6 +105,7 @@ int main(int argc, char *argv[])
         options.add_options()("asc", po::value<std::string>(), "asc bitstream file to write");
         options.add_options()("read", po::value<std::string>(), "asc bitstream file to read");
         options.add_options()("seed", po::value<int>(), "seed value for random number generator");
+        options.add_options()("slack_redist_iter", po::value<int>(), "number of iterations between slack redistribution");
         options.add_options()("version,V", "show version");
         options.add_options()("tmfuzz", "run path delay estimate fuzzer");
         options.add_options()("test", "check architecture database integrity");
@@ -302,6 +303,10 @@ int main(int argc, char *argv[])
             ctx->rngseed(vm["seed"].as<int>());
         }
 
+        if (vm.count("slack_redist_iter")) {
+            ctx->slack_redist_iter = vm["slack_redist_iter"].as<int>();
+        }
+
         if (vm.count("svg")) {
             std::cout << "<svg xmlns=\"http://www.w3.org/2000/svg\" "
                          "xmlns:xlink=\"http://www.w3.org/1999/xlink\">\n";
@@ -411,7 +416,6 @@ int main(int argc, char *argv[])
 
             if (!ctx->pack() && !ctx->force)
                 log_error("Packing design failed.\n");
-            //assign_budget(ctx.get());
             ctx->check();
             print_utilisation(ctx.get());
             if (!vm.count("pack-only")) {