Improving the SA+legalisation flow

Signed-off-by: David Shah <davey1576@gmail.com>

6 files changed, 12 insertions, 7 deletions

diff --git a/common/nextpnr.h b/common/nextpnr.h
index 8d4714bf..b647d44c 100644
--- a/common/nextpnr.h
+++ b/common/nextpnr.h
@@ -230,7 +230,7 @@ struct Context : Arch
     bool debug = false;
     bool force = false;
     bool timing_driven = true;
-
+    float target_freq = 12e6;
     Context(ArchArgs args) : Arch(args) {}
 
     // --------------------------------------------------------------
diff --git a/common/place_common.cc b/common/place_common.cc
index 95faf67f..60735890 100644
--- a/common/place_common.cc
+++ b/common/place_common.cc
@@ -91,7 +91,7 @@ wirelen_t get_cell_wirelength(const Context *ctx, const CellInfo *cell)
     return wirelength;
 }
 
-static wirelen_t get_cell_wirelength_at_bel(const Context *ctx, CellInfo *cell, BelId bel)
+wirelen_t get_cell_wirelength_at_bel(const Context *ctx, CellInfo *cell, BelId bel)
 {
     BelId oldBel = cell->bel;
     cell->bel = bel;
diff --git a/common/place_common.h b/common/place_common.h
index f58da450..67956072 100644
--- a/common/place_common.h
+++ b/common/place_common.h
@@ -32,6 +32,9 @@ wirelen_t get_net_wirelength(const Context *ctx, const NetInfo *net, float &tns)
 // Return the wirelength of all nets connected to a cell
 wirelen_t get_cell_wirelength(const Context *ctx, const CellInfo *cell);
 
+// Return the wirelength of all nets connected to a cell, when the cell is at a given bel
+wirelen_t get_cell_wirelength_at_bel(const Context *ctx, CellInfo *cell, BelId bel);
+
 // Place a single cell in the lowest wirelength Bel available, optionally requiring validity check
 bool place_single_cell(Context *ctx, CellInfo *cell, bool require_legality);
 
diff --git a/common/place_sa.cc b/common/place_sa.cc
index c0c1b180..b773bb68 100644
--- a/common/place_sa.cc
+++ b/common/place_sa.cc
@@ -207,7 +207,8 @@ class SAPlacer
                         temp *= 0.8;
                 }
             }
-
+            // Once cooled below legalise threshold, run legalisation and start requiring
+            // legal moves only
             if (temp < legalise_temp && !require_legal) {
                 legalise_design(ctx);
                 require_legal = true;
@@ -219,6 +220,7 @@ class SAPlacer
                 temp = post_legalise_temp;
                 diameter *= post_legalise_dia_scale;
                 ctx->shuffle(autoplaced);
+                assign_budget(ctx);
             }
 
             // Recalculate total wirelength entirely to avoid rounding errors
diff --git a/common/timing.cc b/common/timing.cc
index 9b10068e..3a48935f 100644
--- a/common/timing.cc
+++ b/common/timing.cc
@@ -70,12 +70,12 @@ static delay_t follow_net(Context *ctx, NetInfo *net, int path_length, delay_t s
     return net_budget;
 }
 
-void assign_budget(Context *ctx, float default_clock)
+void assign_budget(Context *ctx)
 {
     log_break();
     log_info("Annotating ports with timing budgets\n");
     // Clear delays to a very high value first
-    delay_t default_slack = delay_t(1.0e12 / default_clock);
+    delay_t default_slack = delay_t(1.0e12 / ctx->target_freq);
     for (auto &net : ctx->nets) {
         for (auto &usr : net.second->users) {
             usr.budget = default_slack;
@@ -87,7 +87,7 @@ void assign_budget(Context *ctx, float default_clock)
             if (port.second.type == PORT_OUT) {
                 IdString clock_domain = ctx->getPortClock(cell.second.get(), port.first);
                 if (clock_domain != IdString()) {
-                    delay_t slack = delay_t(1.0e12 / default_clock); // TODO: clock constraints
+                    delay_t slack = delay_t(1.0e12 / ctx->target_freq); // TODO: clock constraints
                     if (port.second.net)
                         follow_net(ctx, port.second.net, 0, slack);
                 }
diff --git a/common/timing.h b/common/timing.h
index 03ae048d..025e4a76 100644
--- a/common/timing.h
+++ b/common/timing.h
@@ -25,7 +25,7 @@
 NEXTPNR_NAMESPACE_BEGIN
 
 // Assign "budget" values for all user ports in the design
-void assign_budget(Context *ctx, float default_clock = 12e6);
+void assign_budget(Context *ctx);
 
 NEXTPNR_NAMESPACE_END